feat(asm): emit linkable ELF and Mach-O objects with external symbols

Assisted-by: Qwen 3.8 Max Preview

arch/arch.go

@@ -156,6 +156,16 @@ func (t *Table) Lookup(mnemonic string) (Instr, bool) {
 			}
 		}
 	}
+	// amd64 EVEX instructions take a .Z zeroing suffix (masking is written as
+	// an explicit K operand rather than a suffix); strip it so the base
+	// instruction is still recognised.
+	if t.Arch == AMD64 {
+		if base, ok := strings.CutSuffix(key, ".Z"); ok {
+			if in, found := t.instrs[base]; found {
+				return in, true
+			}
+		}
+	}
 	return Instr{}, false
 }
 

asm/assemble.go

@@ -30,9 +30,12 @@ func Assemble(t *ast.Text) ([]byte, map[string]int, error) {
 // linkInfo carries file-level symbol context into a single-function assembly:
 // the set of static symbols a GLOBL in the same file defines.  A nil link
 // rejects SB operands outright (single-function assembly cannot resolve
-// them).
+// them).  When allowExternal is set, a reference to a symbol no GLOBL in the
+// file defines is recorded as an external relocation instead of failing —
+// the object-file emitters resolve it at link time.
 type linkInfo struct {
 	symbols       map[string]bool
+	allowExternal bool
 }
 
 // sbPatch is a function-relative static-symbol relocation: the disp32 field
@@ -425,8 +428,10 @@ func operandFromAST(op *ast.Operand, size int, fi frameInfo, link *linkInfo) (Op
 				if a.Sym.Static {
 					return nil, fmt.Errorf("undefined symbol %q", a.Sym.Name)
 				}
+				if !link.allowExternal {
 					return nil, fmt.Errorf("external symbol %q needs object-file emission", a.Sym.Name)
 				}
+			}
 			return sbMem{size: size, name: a.Sym.Name, addend: a.Sym.Offset}, nil
 		}
 

asm/elf.go

@@ -0,0 +1,301 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+package asm
+
+import (
+	"encoding/binary"
+	"fmt"
+)
+
+// This file emits ELF64 relocatable objects (ET_REL) from an assembled
+// Image: a .text section holding the function bodies, a .data section
+// holding the GLOBL initialisers, a symbol table with one symbol per TEXT
+// and GLOBL (file-local <> symbols are STB_LOCAL, the rest STB_GLOBAL), and
+// a .rela.text relocation table — one R_X86_64_PC32 entry per static-symbol
+// reference, internal references resolving against the local data symbols
+// and external ones against undefined globals.  The output links with the
+// system toolchain (cc/ld) the way a hand-assembled .o would.
+
+// ELF constants (ELF64, little-endian, System V).
+const (
+	elfClass64 = 2
+	elfDataLSB = 1
+	elfVersion = 1
+
+	etREL   = 1 // relocatable object
+	emX8664 = 62
+
+	shtNull     = 0
+	shtProgbits = 1
+	shtSymtab   = 2
+	shtStrtab   = 3
+	shtRela     = 4
+
+	shfWrite     = 1
+	shfAlloc     = 2
+	shfExecInstr = 4
+
+	stbLocal  = 0
+	stbGlobal = 1
+
+	sttNotype   = 0
+	sttObject   = 1
+	sttFunc     = 2
+	sttSection  = 3
+	stInfoShift = 4
+
+	shnUndef = 0
+
+	rX8664PC32 = 2
+)
+
+// elfSym is one symbol-table entry in construction.
+type elfSym struct {
+	name  string
+	info  byte
+	shndx uint16
+	value uint64
+	size  uint64
+}
+
+// ELFObject returns the image as an ELF64 relocatable object file, ready for
+// the system linker.  Symbol names are the TEXT and GLOBL identifiers as
+// written (the middle dot stripped); a package prefix, when present, is
+// joined with a dot.  Every static-symbol reference becomes an
+// R_X86_64_PC32 relocation, so the code is position-independent and links
+// at any address.
+func (img *Image) ELFObject() ([]byte, error) {
+	le := binary.LittleEndian
+
+	// Section indices: 0 NULL, 1 .text, 2 .data; the tables follow.
+	const (
+		secText = 1
+		secData = 2
+	)
+
+	// Build the symbol table: the null entry and the two section symbols
+	// come first, then the local symbols (static TEXT and GLOBL), then the
+	// globals (exported TEXT and GLOBL, and the undefined externals) — ELF
+	// requires every local to precede every global, and sh_info records the
+	// boundary.  symIdx maps a symbol name to its index for the relocations.
+	var locals, globals []elfSym
+	for _, fn := range img.Funcs {
+		s := elfSym{
+			name:  objectName(fn.Pkg, fn.Name),
+			info:  sttFunc,
+			shndx: secText,
+			value: uint64(fn.Offset),
+			size:  uint64(fn.Size),
+		}
+		if fn.Static {
+			locals = append(locals, s)
+		} else {
+			s.info |= stbGlobal << stInfoShift
+			globals = append(globals, s)
+		}
+	}
+	for _, d := range img.DataSyms {
+		s := elfSym{
+			name:  objectName(d.Pkg, d.Name),
+			info:  sttObject,
+			shndx: secData,
+			value: uint64(d.Offset),
+			size:  uint64(d.Size),
+		}
+		if d.Static {
+			locals = append(locals, s)
+		} else {
+			s.info |= stbGlobal << stInfoShift
+			globals = append(globals, s)
+		}
+	}
+	for _, name := range img.Externals {
+		globals = append(globals, elfSym{name: name, info: stbGlobal << stInfoShift})
+	}
+	syms := []elfSym{
+		{}, // the mandatory null entry
+		{name: ".text", info: sttSection, shndx: secText},
+		{name: ".data", info: sttSection, shndx: secData},
+	}
+	syms = append(syms, locals...)
+	shInfo := len(syms) // first global symbol
+	syms = append(syms, globals...)
+	symIdx := map[string]int{}
+	for i, s := range syms {
+		symIdx[s.name] = i
+	}
+
+	// Build the relocations.
+	type elfRela struct {
+		off    uint64
+		sym    int
+		addend int64
+	}
+	var relas []elfRela
+	for _, fn := range img.Funcs {
+		for _, r := range fn.Relocs {
+			idx, ok := symIdx[r.Name]
+			if !ok {
+				return nil, fmt.Errorf("relocation references unknown symbol %q", r.Name)
+			}
+			relas = append(relas, elfRela{
+				off: uint64(fn.Offset + r.Off),
+				sym: idx,
+				// R_X86_64_PC32 computes S + A − P with P the patch site; the
+				// assembler measures the symbol from the instruction end,
+				// After − Off bytes past the field, so the addend carries
+				// that distance with a negative sign.
+				addend: r.Addend - int64(r.After-r.Off),
+			})
+		}
+	}
+
+	// Serialise the string tables.
+	stNames := newElfStrtab()
+	for _, s := range syms {
+		stNames.add(s.name)
+	}
+	stSections := newElfStrtab()
+	for _, n := range []string{".text", ".data", ".symtab", ".strtab", ".rela.text", ".shstrtab"} {
+		stSections.add(n)
+	}
+
+	// Section presence: .rela.text only when there are relocations.
+	hasRela := len(relas) > 0
+	nSections := 6 // NULL, .text, .data, .symtab, .strtab, .shstrtab
+	if hasRela {
+		nSections = 7
+	}
+	secSymtab, secStrtab := 3, 4
+	secShstr := nSections - 1
+
+	// Lay the file out: header, section data, section headers.
+	var out []byte
+	out = append(out, make([]byte, 64)...) // ELF header, filled last
+
+	align := func(n int) {
+		for len(out)%n != 0 {
+			out = append(out, 0)
+		}
+	}
+
+	align(16)
+	textOff := len(out)
+	out = append(out, img.Code...)
+
+	align(16)
+	dataOff := len(out)
+	out = append(out, img.Data...)
+
+	align(8)
+	symtabOff := len(out)
+	for _, s := range syms {
+		var b [24]byte
+		le.PutUint32(b[0:], uint32(stNames.at(s.name)))
+		b[4] = s.info
+		b[5] = 0 // st_other
+		le.PutUint16(b[6:], s.shndx)
+		le.PutUint64(b[8:], s.value)
+		le.PutUint64(b[16:], s.size)
+		out = append(out, b[:]...)
+	}
+
+	strtabOff := len(out)
+	out = append(out, stNames.bytes()...)
+
+	var relaOff int
+	if hasRela {
+		align(8)
+		relaOff = len(out)
+		for _, r := range relas {
+			var b [24]byte
+			le.PutUint64(b[0:], r.off)
+			le.PutUint64(b[8:], uint64(r.sym)<<32|rX8664PC32)
+			le.PutUint64(b[16:], uint64(r.addend))
+			out = append(out, b[:]...)
+		}
+	}
+
+	shstrOff := len(out)
+	out = append(out, stSections.bytes()...)
+
+	align(8)
+	shoff := len(out)
+
+	// Section headers.
+	putSh := func(name string, typ int, flags uint64, off, size int, link, info int, alignV, entsize uint64) {
+		var b [64]byte
+		le.PutUint32(b[0:], uint32(stSections.at(name)))
+		le.PutUint32(b[4:], uint32(typ))
+		le.PutUint64(b[8:], flags)
+		le.PutUint64(b[16:], 0) // sh_addr
+		le.PutUint64(b[24:], uint64(off))
+		le.PutUint64(b[32:], uint64(size))
+		le.PutUint32(b[40:], uint32(link))
+		le.PutUint32(b[44:], uint32(info))
+		le.PutUint64(b[48:], alignV)
+		le.PutUint64(b[56:], entsize)
+		out = append(out, b[:]...)
+	}
+	putSh("", shtNull, 0, 0, 0, 0, 0, 0, 0)
+	putSh(".text", shtProgbits, shfAlloc|shfExecInstr, textOff, len(img.Code), 0, 0, 16, 0)
+	putSh(".data", shtProgbits, shfAlloc|shfWrite, dataOff, len(img.Data), 0, 0, 16, 0)
+	putSh(".symtab", shtSymtab, 0, symtabOff, 24*len(syms), secStrtab, shInfo, 8, 24)
+	putSh(".strtab", shtStrtab, 0, strtabOff, len(stNames.bytes()), 0, 0, 1, 0)
+	if hasRela {
+		putSh(".rela.text", shtRela, 0, relaOff, 24*len(relas), secSymtab, secText, 8, 24)
+	}
+	putSh(".shstrtab", shtStrtab, 0, shstrOff, len(stSections.bytes()), 0, 0, 1, 0)
+
+	// The ELF header.
+	hdr := out[:64]
+	copy(hdr[0:], []byte{0x7f, 'E', 'L', 'F', elfClass64, elfDataLSB, elfVersion, 0})
+	le.PutUint16(hdr[16:], etREL)
+	le.PutUint16(hdr[18:], emX8664)
+	le.PutUint32(hdr[20:], elfVersion)
+	le.PutUint64(hdr[24:], 0)             // e_entry
+	le.PutUint64(hdr[32:], 0)             // e_phoff
+	le.PutUint64(hdr[40:], uint64(shoff)) // e_shoff
+	le.PutUint32(hdr[48:], 0)             // e_flags
+	le.PutUint16(hdr[52:], 64)            // e_ehsize
+	le.PutUint16(hdr[54:], 0)             // e_phentsize
+	le.PutUint16(hdr[56:], 0)             // e_phnum
+	le.PutUint16(hdr[58:], 64)            // e_shentsize
+	le.PutUint16(hdr[60:], uint16(nSections))
+	le.PutUint16(hdr[62:], uint16(secShstr))
+
+	return out, nil
+}
+
+// objectName renders a symbol's object-file name: the identifier as written,
+// with an explicit package prefix joined by a dot.
+func objectName(pkg, name string) string {
+	if pkg == "" {
+		return name
+	}
+	return pkg + "." + name
+}
+
+// elfStrtab is an ELF string table under construction.
+type elfStrtab struct {
+	buf []byte
+	off map[string]int
+}
+
+func newElfStrtab() *elfStrtab {
+	return &elfStrtab{buf: []byte{0}, off: map[string]int{"": 0}}
+}
+
+func (s *elfStrtab) add(name string) {
+	if _, ok := s.off[name]; ok {
+		return
+	}
+	s.off[name] = len(s.buf)
+	s.buf = append(s.buf, name...)
+	s.buf = append(s.buf, 0)
+}
+
+func (s *elfStrtab) at(name string) int { return s.off[name] }
+
+func (s *elfStrtab) bytes() []byte { return s.buf }

asm/elf_test.go

@@ -0,0 +1,310 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+package asm
+
+import (
+	"bytes"
+	"debug/elf"
+	"encoding/binary"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+
+	"sourcedock.dev/petrbalvin/gasm-devkit/parser"
+)
+
+// The object-file tests share one source: two exported functions, one
+// file-local constant reached through a relocation, and one external symbol
+// the linker must resolve.  The functions take their arguments in the System
+// V registers (not the Go stack ABI) so a C driver can call them directly.
+const elfTestSrc = `
+#include "textflag.h"
+
+TEXT ·addq(SB), NOSPLIT, $0
+	LEAQ (DI)(SI*1), AX
+	RET
+
+TEXT ·getanswer(SB), NOSPLIT, $0
+	MOVQ answer<>(SB), AX
+	RET
+
+TEXT ·useextern(SB), NOSPLIT, $0
+	MOVQ extvar(SB), AX
+	RET
+
+GLOBL answer<>(SB), RODATA, $8
+DATA answer<>+0(SB)/8, $42
+`
+
+func elfTestImage(t *testing.T) *Image {
+	t.Helper()
+	f, errs := parser.Parse("t_amd64.s", elfTestSrc)
+	if len(errs) > 0 {
+		t.Fatalf("parse: %v", errs)
+	}
+	img, err := AssembleFile(f)
+	if err != nil {
+		t.Fatalf("AssembleFile: %v", err)
+	}
+	return img
+}
+
+// TestAssembleFileExternals checks that a reference to a symbol no GLOBL
+// defines is recorded as an external relocation instead of failing — the
+// raw image leaves the displacement zero, the object emitters carry it.
+func TestAssembleFileExternals(t *testing.T) {
+	img := elfTestImage(t)
+	if len(img.Externals) != 1 || img.Externals[0] != "extvar" {
+		t.Fatalf("Externals = %v, want [extvar]", img.Externals)
+	}
+	var ext, local int
+	for _, fn := range img.Funcs {
+		for _, r := range fn.Relocs {
+			if r.External {
+				ext++
+				if r.Name != "extvar" {
+					t.Errorf("external reloc names %q, want extvar", r.Name)
+				}
+			} else {
+				local++
+				if r.Name != "answer" {
+					t.Errorf("local reloc names %q, want answer", r.Name)
+				}
+			}
+		}
+	}
+	if ext != 1 || local != 1 {
+		t.Errorf("relocs = %d external, %d local; want 1 and 1", ext, local)
+	}
+}
+
+// TestELFObject checks the structure of the emitted ELF64 relocatable
+// object: sections, the symbol table (bindings, types, values, sizes) and
+// the .rela.text relocations, parsed back with debug/elf.
+func TestELFObject(t *testing.T) {
+	img := elfTestImage(t)
+	obj, err := img.ELFObject()
+	if err != nil {
+		t.Fatalf("ELFObject: %v", err)
+	}
+	f, err := elf.NewFile(bytes.NewReader(obj))
+	if err != nil {
+		t.Fatalf("parse emitted object: %v", err)
+	}
+	defer f.Close()
+
+	if f.Type != elf.ET_REL || f.Machine != elf.EM_X86_64 {
+		t.Errorf("type/machine = %v/%v, want ET_REL/EM_X86_64", f.Type, f.Machine)
+	}
+
+	text := f.Section(".text")
+	data := f.Section(".data")
+	if text == nil || data == nil {
+		t.Fatal("missing .text or .data section")
+	}
+	if text.Flags&elf.SHF_EXECINSTR == 0 || text.Flags&elf.SHF_ALLOC == 0 {
+		t.Errorf(".text flags = %v", text.Flags)
+	}
+	if data.Flags&elf.SHF_WRITE == 0 {
+		t.Errorf(".data flags = %v", data.Flags)
+	}
+	textData, err := text.Data()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(textData, img.Code) {
+		t.Errorf(".text contents differ from the image code")
+	}
+
+	syms, err := f.Symbols()
+	if err != nil {
+		t.Fatalf("symbols: %v", err)
+	}
+	byName := map[string]elf.Symbol{}
+	for _, s := range syms {
+		byName[s.Name] = s
+	}
+	wantSym := func(name string, bind elf.SymBind, typ elf.SymType, section elf.SectionIndex, size uint64) {
+		t.Helper()
+		s, ok := byName[name]
+		if !ok {
+			t.Errorf("symbol %q not found", name)
+			return
+		}
+		if elf.ST_BIND(s.Info) != bind || elf.ST_TYPE(s.Info) != typ {
+			t.Errorf("%s: bind/type = %v/%v, want %v/%v", name, elf.ST_BIND(s.Info), elf.ST_TYPE(s.Info), bind, typ)
+		}
+		if s.Section != section {
+			t.Errorf("%s: section = %v, want %v", name, s.Section, section)
+		}
+		if s.Size != size {
+			t.Errorf("%s: size = %d, want %d", name, s.Size, size)
+		}
+	}
+	// The emitted layout is fixed: 0 NULL, 1 .text, 2 .data.
+	if f.Sections[1].Name != ".text" || f.Sections[2].Name != ".data" {
+		t.Fatalf("section layout = %s, %s; want .text, .data", f.Sections[1].Name, f.Sections[2].Name)
+	}
+	textIdx := elf.SectionIndex(1)
+	dataIdx := elf.SectionIndex(2)
+	wantSym("addq", elf.STB_GLOBAL, elf.STT_FUNC, textIdx, 5)
+	wantSym("getanswer", elf.STB_GLOBAL, elf.STT_FUNC, textIdx, 8)
+	wantSym("useextern", elf.STB_GLOBAL, elf.STT_FUNC, textIdx, 8)
+	wantSym("answer", elf.STB_LOCAL, elf.STT_OBJECT, dataIdx, 8)
+	wantSym("extvar", elf.STB_GLOBAL, elf.STT_NOTYPE, elf.SHN_UNDEF, 0)
+
+	// Relocations: one for the file-local constant (resolving against the
+	// local data symbol) and one for the external (against the undefined
+	// global), both R_X86_64_PC32 with the −4 addend the PC-relative form
+	// needs.  debug/elf does not surface rela entries, so read the section
+	// directly.
+	relaSec := f.Section(".rela.text")
+	if relaSec == nil {
+		t.Fatal("missing .rela.text")
+	}
+	raw, err := relaSec.Data()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(raw)%24 != 0 || len(raw)/24 != 2 {
+		t.Fatalf(".rela.text has %d bytes, want two 24-byte entries", len(raw))
+	}
+	// Symbol names straight from the raw tables: r_info carries an index
+	// into .symtab including the null entry, which debug/elf's Symbols()
+	// slice may not mirror.
+	symtabRaw, err := f.Section(".symtab").Data()
+	if err != nil {
+		t.Fatal(err)
+	}
+	strtabRaw, err := f.Section(".strtab").Data()
+	if err != nil {
+		t.Fatal(err)
+	}
+	symName := func(idx int) string {
+		stName := binary.LittleEndian.Uint32(symtabRaw[idx*24:])
+		end := bytes.IndexByte(strtabRaw[stName:], 0)
+		return string(strtabRaw[stName : int(stName)+end])
+	}
+	for i := 0; i < 2; i++ {
+		e := raw[i*24 : (i+1)*24]
+		off := binary.LittleEndian.Uint64(e[0:])
+		info := binary.LittleEndian.Uint64(e[8:])
+		addend := int64(binary.LittleEndian.Uint64(e[16:]))
+		typ := info & 0xffffffff
+		sym := int(info >> 32)
+		if typ != uint64(elf.R_X86_64_PC32) {
+			t.Errorf("reloc %d: type %d, want R_X86_64_PC32", i, typ)
+		}
+		if addend != -4 {
+			t.Errorf("reloc %d: addend %d, want -4", i, addend)
+		}
+		if name := symName(sym); name != "answer" && name != "extvar" {
+			t.Errorf("reloc %d: symbol %q, want answer or extvar", i, name)
+		}
+		// The relocation offset lands on the disp32 field: the four bytes
+		// before a RET-terminated eight-byte MOVQ.
+		if off+4 > uint64(len(textData)) {
+			t.Errorf("reloc %d: offset %d outside .text", i, off)
+		}
+	}
+}
+
+// TestELFObjectNoRelocations checks a file with no static-symbol references
+// emits a valid object without a .rela.text section.
+func TestELFObjectNoRelocations(t *testing.T) {
+	f, errs := parser.Parse("n_amd64.s", `
+#include "textflag.h"
+TEXT ·nop(SB), NOSPLIT, $0
+	RET
+`)
+	if len(errs) > 0 {
+		t.Fatalf("parse: %v", errs)
+	}
+	img, err := AssembleFile(f)
+	if err != nil {
+		t.Fatalf("AssembleFile: %v", err)
+	}
+	obj, err := img.ELFObject()
+	if err != nil {
+		t.Fatalf("ELFObject: %v", err)
+	}
+	ef, err := elf.NewFile(bytes.NewReader(obj))
+	if err != nil {
+		t.Fatalf("parse emitted object: %v", err)
+	}
+	defer ef.Close()
+	if ef.Section(".rela.text") != nil {
+		t.Error("unexpected .rela.text section")
+	}
+	syms, err := ef.Symbols()
+	if err != nil {
+		t.Fatal(err)
+	}
+	found := false
+	for _, s := range syms {
+		if s.Name == "nop" && elf.ST_TYPE(s.Info) == elf.STT_FUNC {
+			found = true
+		}
+	}
+	if !found {
+		t.Error("function symbol nop not found")
+	}
+}
+
+// TestELFLinkAndRun is the end-to-end check: assemble the test functions,
+// link the emitted object with a C driver that defines the external symbol,
+// and run the result.  Skipped when no C compiler is available.
+func TestELFLinkAndRun(t *testing.T) {
+	cc, err := exec.LookPath("cc")
+	if err != nil {
+		t.Skip("no C compiler available")
+	}
+	dir := t.TempDir()
+
+	img := elfTestImage(t)
+	obj, err := img.ELFObject()
+	if err != nil {
+		t.Fatalf("ELFObject: %v", err)
+	}
+	objPath := filepath.Join(dir, "t.o")
+	if err := os.WriteFile(objPath, obj, 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	const driver = `
+#include <stdio.h>
+
+long addq(long a, long b);
+long getanswer(void);
+long useextern(void);
+
+long extvar = 7;
+
+int main(void) {
+	printf("%ld %ld %ld\n", addq(41, 1), getanswer(), useextern());
+	return 0;
+}
+`
+	driverPath := filepath.Join(dir, "driver.c")
+	if err := os.WriteFile(driverPath, []byte(driver), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	// -no-pie: the encoder emits R_X86_64_PC32 for external references,
+	// which a position-independent executable would reject (it wants
+	// PLT32/GOT relocations, a future increment).
+	appPath := filepath.Join(dir, "app")
+	out, err := exec.Command(cc, "-no-pie", "-o", appPath, driverPath, objPath).CombinedOutput()
+	if err != nil {
+		t.Fatalf("link failed: %v\n%s", err, out)
+	}
+	run, err := exec.Command(appPath).CombinedOutput()
+	if err != nil {
+		t.Fatalf("run failed: %v\n%s", err, run)
+	}
+	if got := string(run); got != "42 42 7\n" {
+		t.Errorf("output %q, want \"42 42 7\\n\"", got)
+	}
+}

asm/encode.go

@@ -51,9 +51,16 @@ func (e *enc) encode(mnem string, ops []Operand) error {
 
 	// VEX (AVX/AVX2) and EVEX (AVX-512) instructions: the trailing
 	// B/W/L/Q/D is part of the mnemonic, not a size suffix, so dispatch
-	// before splitSize.
-	if isVex(upper) || isEvex(upper) || upper == "KMOVW" {
-		return e.encodeVec(upper, ops)
+	// before splitSize.  A ".Z" suffix requests EVEX zeroing.
+	base, zeroing, err := stripEvexSuffix(upper)
+	if err != nil {
+		return err
+	}
+	if isVex(base) || isEvex(base) || base == "KMOVW" {
+		return e.encodeVec(base, ops, zeroing)
+	}
+	if zeroing {
+		return fmt.Errorf("%s: the .Z suffix requires an EVEX instruction", mnem)
 	}
 
 	// CMOVcc and SETcc carry the condition in the mnemonic (CMOVLGT, SETNE).
@@ -121,14 +128,20 @@ func splitSize(upper string) (base string, size int) {
 // its own direction-dependent opcodes; KTESTW is always VEX; everything else
 // takes EVEX when an operand demands it (a ZMM or K register, or an
 // EVEX-only mnemonic) and VEX otherwise.
-func (e *enc) encodeVec(upper string, ops []Operand) error {
+func (e *enc) encodeVec(upper string, ops []Operand, zeroing bool) error {
 	if upper == "KMOVW" {
+		if zeroing {
+			return fmt.Errorf("KMOVW takes no .Z suffix")
+		}
 		return e.encodeKmovw(ops)
 	}
 	if upper == "KTESTW" || !evexRequired(upper, ops) {
+		if zeroing {
+			return fmt.Errorf("%s: the .Z suffix requires an EVEX instruction", upper)
+		}
 		return e.encodeVex(upper, ops)
 	}
-	return e.encodeEvex(upper, ops)
+	return e.encodeEvex(upper, ops, zeroing)
 }
 
 // --- instruction components -------------------------------------------------

asm/evex.go

@@ -3,14 +3,19 @@
 
 package asm
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 // This file implements EVEX (AVX-512) instruction encoding: the four-byte
 // EVEX prefix with 5-bit vector register fields (Z0–Z31, X/Y 16–31), the
 // compressed disp8×N displacement, and the operand shapes the go-flac
-// AVX-512 kernels use.  Masking ({k}) and zeroing ({z}) are not supported —
-// the kernels do not use them.  K-register operands (mask destinations,
-// KMOVW, KTESTW) are.
+// AVX-512 kernels use plus the common floating-point and conversion set.
+// Masking follows the Go assembler's spelling: an explicit K1–K7 operand
+// anywhere among the operands (merging) plus a ".Z" mnemonic suffix for
+// zeroing.  K-register operands (mask destinations, KMOVW, KTESTW) are
+// supported too.
 
 // evexSpec describes one EVEX instruction's encoding parameters.  The form
 // field reuses the vexForm shapes, which carry over unchanged.
@@ -46,6 +51,31 @@ var evexTable = map[string]evexSpec{
 	// EVEX.128/256/512.66.0F.W1 — packed double arithmetic.
 	"VADDPD": {1, 0x58, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
 	"VMULPD": {1, 0x59, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VSUBPD": {1, 0x5C, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VDIVPD": {1, 0x5E, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VMINPD": {1, 0x5D, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VMAXPD": {1, 0x5F, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	// EVEX.128/256/512.66.0F.W1 — packed double unpack.
+	"VUNPCKLPD": {1, 0x14, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VUNPCKHPD": {1, 0x15, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+
+	// EVEX.128.F2.0F.W1 — scalar double arithmetic (the packed opcodes with
+	// an F2 pp; the EVEX forms exist for masked and zeroing use).  The
+	// memory operand is a single double, so disp8×N = 8.
+	"VADDSD": {1, 0x58, 1, 3, -1, vexNDS3, [3]int{8, 8, 8}},
+	"VSUBSD": {1, 0x5C, 1, 3, -1, vexNDS3, [3]int{8, 8, 8}},
+	"VMULSD": {1, 0x59, 1, 3, -1, vexNDS3, [3]int{8, 8, 8}},
+	"VDIVSD": {1, 0x5E, 1, 3, -1, vexNDS3, [3]int{8, 8, 8}},
+	"VMINSD": {1, 0x5D, 1, 3, -1, vexNDS3, [3]int{8, 8, 8}},
+	"VMAXSD": {1, 0x5F, 1, 3, -1, vexNDS3, [3]int{8, 8, 8}},
+
+	// EVEX.128.F3.0F.W0 — scalar single arithmetic (disp8×N = 4).
+	"VADDSS": {1, 0x58, 0, 2, -1, vexNDS3, [3]int{4, 4, 4}},
+	"VSUBSS": {1, 0x5C, 0, 2, -1, vexNDS3, [3]int{4, 4, 4}},
+	"VMULSS": {1, 0x59, 0, 2, -1, vexNDS3, [3]int{4, 4, 4}},
+	"VDIVSS": {1, 0x5E, 0, 2, -1, vexNDS3, [3]int{4, 4, 4}},
+	"VMINSS": {1, 0x5D, 0, 2, -1, vexNDS3, [3]int{4, 4, 4}},
+	"VMAXSS": {1, 0x5F, 0, 2, -1, vexNDS3, [3]int{4, 4, 4}},
 
 	// EVEX.512.66.0F3A — align (NDS + imm8).
 	"VALIGND": {3, 0x03, 0, 1, -1, vexNDS3Imm, [3]int{16, 32, 64}},
@@ -59,6 +89,36 @@ var evexTable = map[string]evexSpec{
 	// EVEX.128/256/512.F3.0F.W1 — signed qword to packed double (reg=dst,
 	// rm=src, no vvvv).
 	"VCVTQQ2PD": {1, 0xE6, 1, 2, -1, vexRM, [3]int{16, 32, 64}},
+	// EVEX.128/256/512.F2.0F.W1 — duplicate the low double (reg=dst,
+	// rm=src, no vvvv): a 128-bit destination reads a single double from
+	// memory (disp8×8), the wider ones read the full operand.
+	"VMOVDDUP": {1, 0x12, 1, 3, -1, vexRM, [3]int{8, 32, 64}},
+	// EVEX.128/256/512.0F.W0 — signed dword to packed single (reg=dst,
+	// rm=src, no vvvv, no mandatory prefix — as in the VEX form).
+	"VCVTDQ2PS": {1, 0x5B, 0, 0, -1, vexRM, [3]int{16, 32, 64}},
+	// EVEX.128/256/512.0F.W0 — packed single to packed double: the
+	// destination is twice the source width and sets the length; disp8×N
+	// follows the narrow memory source.  No F3 prefix: the Go assembler
+	// emits this instruction with pp = 00 (Intel's maps would call that
+	// undefined) and gasm reproduces the Go assembler's bytes — its machine
+	// code is the oracle, not the manual.
+	"VCVTPS2PD": {1, 0x5A, 0, 0, -1, vexRM, [3]int{8, 16, 32}},
+	// EVEX.128/256/512.F3.0F.W0 — signed dword to packed double (the EVEX
+	// form of the VEX instruction; the destination sets the length, disp8×N
+	// follows the narrow memory source).
+	"VCVTDQ2PD": {1, 0xE6, 0, 2, -1, vexRM, [3]int{8, 16, 32}},
+	// EVEX packed double → dword conversions: the source is the wide
+	// operand and the mnemonic fixes the length — the bare names are
+	// 512-bit only (ZMM source, XMM destination), the X/Y spellings are
+	// EVEX-128/256.  Exactly one slot of n is valid; it names the vector
+	// length (and the disp8×N multiplier) a register or memory source
+	// encodes.
+	"VCVTPD2DQ":   {1, 0xE6, 1, 3, -1, vexRMSrcLen, [3]int{0, 0, 64}},
+	"VCVTTPD2DQ":  {1, 0xE6, 1, 1, -1, vexRMSrcLen, [3]int{0, 0, 64}},
+	"VCVTPD2DQX":  {1, 0xE6, 1, 3, -1, vexRMSrcLen, [3]int{16, 0, 0}},
+	"VCVTPD2DQY":  {1, 0xE6, 1, 3, -1, vexRMSrcLen, [3]int{0, 32, 0}},
+	"VCVTTPD2DQX": {1, 0xE6, 1, 1, -1, vexRMSrcLen, [3]int{16, 0, 0}},
+	"VCVTTPD2DQY": {1, 0xE6, 1, 1, -1, vexRMSrcLen, [3]int{0, 32, 0}},
 	// EVEX.128/256/512.66.0F38.W0 — sign-extend dwords to qwords; the memory
 	// operand is the narrow source, so disp8×N follows its size (8/16/32 for
 	// the xmm/ymm/zmm destination lengths).
@@ -74,6 +134,48 @@ var evexTable = map[string]evexSpec{
 	"VPMULLQ": {2, 0x40, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
 	"VPERMD":  {2, 0x36, 0, 1, -1, vexNDS3, [3]int{0, 32, 64}},
 
+	// EVEX.128/256/512 — the wider integer set (AVX-512 F/BW): byte/word
+	// arithmetic, the bitwise ops with D/Q suffixes, min/max, averages and
+	// variable shifts.  All NDS form; W distinguishes element size.
+	"VPADDB":  {1, 0xFC, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPADDW":  {1, 0xFD, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPSUBB":  {1, 0xF8, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPSUBW":  {1, 0xF9, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMULLW": {1, 0xD5, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPAVGB":  {1, 0xE0, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPAVGW":  {1, 0xE3, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMINUB": {1, 0xDA, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMAXUB": {1, 0xDE, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMINSW": {1, 0xEA, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMAXSW": {1, 0xEE, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPANDD":  {1, 0xDB, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPANDQ":  {1, 0xDB, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPANDND": {1, 0xDF, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPANDNQ": {1, 0xDF, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMINSB": {2, 0x38, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMAXSB": {2, 0x3C, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMINSQ": {2, 0x39, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMAXSQ": {2, 0x3D, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMINUW": {2, 0x3A, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMAXUW": {2, 0x3E, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMINSD": {2, 0x39, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMAXSD": {2, 0x3D, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMINUD": {2, 0x3B, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMAXUD": {2, 0x3F, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMINUQ": {2, 0x3B, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPMAXUQ": {2, 0x3F, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPSLLVD": {2, 0x47, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPSLLVQ": {2, 0x47, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPSRLVD": {2, 0x45, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPSRLVQ": {2, 0x45, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPSRAVD": {2, 0x46, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+	"VPSRAVQ": {2, 0x46, 1, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+
+	// EVEX forms of instructions that also exist in VEX (selected when a ZMM
+	// or K register, or indices 16–31, demand EVEX).
+	"VPSHUFD": {1, 0x70, 0, 1, -1, vexImmRM, [3]int{16, 32, 64}},
+	"VPSHUFB": {2, 0x00, 0, 1, -1, vexNDS3, [3]int{16, 32, 64}},
+
 	// EVEX.66.0F — immediate shift (VPSLLD /6).
 	"VPSLLD": {1, 0x72, 0, 1, 6, vexShiftImm, [3]int{16, 32, 64}},
 
@@ -117,6 +219,13 @@ var evexMoveTable = map[string]evexMoveSpec{
 	"VMOVDQU32": {1, 2, 0x6F, 0x7F, 0, [3]int{16, 32, 64}},
 	// EVEX.128/256/512.F3.0F.W1 — unaligned qword move.
 	"VMOVDQU64": {1, 2, 0x6F, 0x7F, 1, [3]int{16, 32, 64}},
+	// EVEX.128/256/512.F2.0F.W0 — unaligned byte move (byte/word moves use the
+	// F2 prefix, dword/qword moves F3; the element size only changes the tuple
+	// semantics).
+	"VMOVDQU8": {1, 3, 0x6F, 0x7F, 0, [3]int{16, 32, 64}},
+	// EVEX.128/256/512.F2.0F.W1 — unaligned word move (shares the qword
+	// encoding).
+	"VMOVDQU16": {1, 3, 0x6F, 0x7F, 1, [3]int{16, 32, 64}},
 	// EVEX.128/256/512.66.0F.W1 — unaligned packed double move.
 	"VMOVUPD": {1, 1, 0x10, 0x11, 1, [3]int{16, 32, 64}},
 }
@@ -151,13 +260,75 @@ func evexRequired(upper string, ops []Operand) bool {
 	return false
 }
 
-// encodeEvex encodes an EVEX instruction with operands in Plan 9 order.
-func (e *enc) encodeEvex(mnemUpper string, ops []Operand) error {
+// stripEvexSuffix splits a ".Z" zeroing suffix off the mnemonic.  It is the
+// only EVEX suffix supported; Go writes masking as an explicit K operand, not
+// a suffix.
+func stripEvexSuffix(mnem string) (base string, zeroing bool, err error) {
+	i := strings.LastIndexByte(mnem, '.')
+	if i < 0 {
+		return mnem, false, nil
+	}
+	if mnem[i+1:] == "Z" {
+		return mnem[:i], true, nil
+	}
+	return "", false, fmt.Errorf("unsupported EVEX suffix %q", mnem[i+1:])
+}
+
+// splitMask extracts an explicit mask register (K1–K7) from the operand list,
+// returning the remaining operands and the mask index.  K0 is not a usable
+// mask (aaa = 0 means "no mask"), matching the assembler.
+func splitMask(ops []Operand) ([]Operand, int, error) {
+	var rest []Operand
+	mask := 0
+	for _, op := range ops {
+		if r, ok := op.(Reg); ok && r.mask {
+			if mask != 0 {
+				return nil, 0, fmt.Errorf("at most one mask register operand")
+			}
+			if r.idx == 0 {
+				return nil, 0, fmt.Errorf("K0 is not a usable mask register")
+			}
+			mask = r.idx
+			continue
+		}
+		rest = append(rest, op)
+	}
+	return rest, mask, nil
+}
+
+// encodeEvex encodes an EVEX instruction with operands in Plan 9 order.  The
+// mask, when present, is an explicit K1–K7 operand anywhere among the
+// operands; zeroing comes from the .Z mnemonic suffix and requires a mask.
+func (e *enc) encodeEvex(mnemUpper string, ops []Operand, zeroing bool) error {
+	// Mask-destination comparisons (VPCMPEQD …, K1): the last operand is the
+	// destination K register, and any mask sits among the preceding operands.
+	if spec, ok := evexTable[mnemUpper]; ok && spec.form == vexNDS3 && len(ops) > 0 {
+		if dst, ok := ops[len(ops)-1].(Reg); ok && dst.mask {
+			rest, mask, err := splitMask(ops[:len(ops)-1])
+			if err != nil {
+				return err
+			}
+			if zeroing && mask == 0 {
+				return fmt.Errorf("%s: zeroing (.Z) requires a mask register", mnemUpper)
+			}
+			return e.encodeEvexNDS3(spec, append(rest, dst), mask, zeroing)
+		}
+	}
+
+	rest, mask, err := splitMask(ops)
+	if err != nil {
+		return err
+	}
+	if zeroing && mask == 0 {
+		return fmt.Errorf("%s: zeroing (.Z) requires a mask register", mnemUpper)
+	}
+	ops = rest
+
 	if bs, ok := evexBcastTable[mnemUpper]; ok {
-		return e.encodeEvexBcast(bs, ops)
+		return e.encodeEvexBcast(bs, ops, mask, zeroing)
 	}
 	if ms, ok := evexMoveTable[mnemUpper]; ok {
-		return e.encodeEvexMove(mnemUpper, ms, ops)
+		return e.encodeEvexMove(mnemUpper, ms, ops, mask, zeroing)
 	}
 	spec, ok := evexTable[mnemUpper]
 	if !ok {
@@ -165,17 +336,21 @@ func (e *enc) encodeEvex(mnemUpper string, ops []Operand) error {
 	}
 	switch spec.form {
 	case vexNDS3:
-		return e.encodeEvexNDS3(spec, ops)
+		return e.encodeEvexNDS3(spec, ops, mask, zeroing)
 	case vexRM:
-		return e.encodeEvexRM(spec, ops)
+		return e.encodeEvexRM(spec, ops, mask, zeroing)
 	case vexRMRev:
-		return e.encodeEvexRMRev(spec, ops)
+		return e.encodeEvexRMRev(spec, ops, mask, zeroing)
+	case vexImmRM:
+		return e.encodeEvexImmRM(spec, ops, mask, zeroing)
 	case vexShiftImm:
-		return e.encodeEvexShiftImm(spec, ops)
+		return e.encodeEvexShiftImm(spec, ops, mask, zeroing)
 	case vexNDS3Imm:
-		return e.encodeEvexNDS3Imm(spec, ops)
+		return e.encodeEvexNDS3Imm(spec, ops, mask, zeroing)
 	case vexExtract:
-		return e.encodeEvexExtract(spec, ops)
+		return e.encodeEvexExtract(spec, ops, mask, zeroing)
+	case vexRMSrcLen:
+		return e.encodeEvexRMSrcLen(spec, ops, mask, zeroing)
 	}
 	return fmt.Errorf("unhandled EVEX form for %s", mnemUpper)
 }
@@ -183,7 +358,7 @@ func (e *enc) encodeEvex(mnemUpper string, ops []Operand) error {
 // encodeEvexNDS3 encodes the three-operand NDS form: OP src2, src1, dst.  The
 // destination may be an opmask register (VPCMPEQD), in which case the vector
 // length comes from the sources.
-func (e *enc) encodeEvexNDS3(spec evexSpec, ops []Operand) error {
+func (e *enc) encodeEvexNDS3(spec evexSpec, ops []Operand, mask int, zeroing bool) error {
 	if len(ops) != 3 {
 		return fmt.Errorf("EVEX NDS instruction expects 3 operands, got %d", len(ops))
 	}
@@ -203,12 +378,12 @@ func (e *enc) encodeEvexNDS3(spec evexSpec, ops []Operand) error {
 			ll = r.vecLenBit()
 		}
 	}
-	return e.emitEvexFields(spec, ll, dstReg.idx, vvvvReg.idx, src2)
+	return e.emitEvexFields(spec, ll, dstReg.idx, vvvvReg.idx, src2, mask, zeroing)
 }
 
 // encodeEvexRM encodes the two-operand form: OP src, dst (reg=dst, rm=src,
 // no vvvv), e.g. VCVTQQ2PD.
-func (e *enc) encodeEvexRM(spec evexSpec, ops []Operand) error {
+func (e *enc) encodeEvexRM(spec evexSpec, ops []Operand, mask int, zeroing bool) error {
 	if len(ops) != 2 {
 		return fmt.Errorf("EVEX two-operand instruction expects 2 operands, got %d", len(ops))
 	}
@@ -217,12 +392,42 @@ func (e *enc) encodeEvexRM(spec evexSpec, ops []Operand) error {
 	if !ok || !dstReg.isVec() {
 		return fmt.Errorf("EVEX destination must be a vector register")
 	}
-	return e.emitEvexFields(spec, dstReg.vecLenBit(), dstReg.idx, -1, src)
+	return e.emitEvexFields(spec, dstReg.vecLenBit(), dstReg.idx, -1, src, mask, zeroing)
+}
+
+// encodeEvexImmRM encodes the immediate shuffle form: OP $imm, src, dst
+// (reg = dst, rm = src, imm8), e.g. VPSHUFD.
+func (e *enc) encodeEvexImmRM(spec evexSpec, ops []Operand, mask int, zeroing bool) error {
+	if len(ops) != 3 {
+		return fmt.Errorf("shuffle expects 3 operands ($imm, src, dst), got %d", len(ops))
+	}
+	imm, src, dst := ops[0], ops[1], ops[2]
+	immVal, ok := imm.(Imm)
+	if !ok {
+		return fmt.Errorf("shuffle control must be an immediate")
+	}
+	dstReg, ok := dst.(Reg)
+	if !ok || !dstReg.isVec() {
+		return fmt.Errorf("shuffle destination must be a vector register")
+	}
+	ll := dstReg.vecLenBit()
+	if r, ok := src.(Reg); ok && r.isVec() {
+		ll = r.vecLenBit()
+	}
+	immByte, err := imm8(int64(immVal))
+	if err != nil {
+		return err
+	}
+	if err := e.emitEvexFields(spec, ll, dstReg.idx, -1, src, mask, zeroing); err != nil {
+		return err
+	}
+	e.out = append(e.out, immByte)
+	return nil
 }
 
 // encodeEvexShiftImm encodes an immediate shift: OP $imm, src, dst
 // (ModRM.reg = /digit, vvvv = dst, rm = src, imm8), e.g. VPSRAD $31, Z3, Z5.
-func (e *enc) encodeEvexShiftImm(spec evexSpec, ops []Operand) error {
+func (e *enc) encodeEvexShiftImm(spec evexSpec, ops []Operand, mask int, zeroing bool) error {
 	if len(ops) != 3 {
 		return fmt.Errorf("EVEX shift expects 3 operands ($imm, src, dst), got %d", len(ops))
 	}
@@ -243,7 +448,7 @@ func (e *enc) encodeEvexShiftImm(spec evexSpec, ops []Operand) error {
 	if err != nil {
 		return err
 	}
-	if err := e.emitEvexFields(spec, dstReg.vecLenBit(), spec.opdigit, dstReg.idx, srcReg); err != nil {
+	if err := e.emitEvexFields(spec, dstReg.vecLenBit(), spec.opdigit, dstReg.idx, srcReg, mask, zeroing); err != nil {
 		return err
 	}
 	e.out = append(e.out, immByte)
@@ -252,7 +457,7 @@ func (e *enc) encodeEvexShiftImm(spec evexSpec, ops []Operand) error {
 
 // encodeEvexNDS3Imm encodes OP $imm, src2, src1, dst (reg=dst, vvvv=src1,
 // rm=src2, imm8), e.g. VALIGND.
-func (e *enc) encodeEvexNDS3Imm(spec evexSpec, ops []Operand) error {
+func (e *enc) encodeEvexNDS3Imm(spec evexSpec, ops []Operand, mask int, zeroing bool) error {
 	if len(ops) != 4 {
 		return fmt.Errorf("instruction expects 4 operands ($imm, src2, src1, dst), got %d", len(ops))
 	}
@@ -273,7 +478,7 @@ func (e *enc) encodeEvexNDS3Imm(spec evexSpec, ops []Operand) error {
 	if err != nil {
 		return err
 	}
-	if err := e.emitEvexFields(spec, dstReg.vecLenBit(), dstReg.idx, vvvvReg.idx, src2); err != nil {
+	if err := e.emitEvexFields(spec, dstReg.vecLenBit(), dstReg.idx, vvvvReg.idx, src2, mask, zeroing); err != nil {
 		return err
 	}
 	e.out = append(e.out, immByte)
@@ -282,7 +487,7 @@ func (e *enc) encodeEvexNDS3Imm(spec evexSpec, ops []Operand) error {
 
 // encodeEvexExtract encodes OP $imm, zsrc, ydst (reg=ZMM source, rm=YMM/memory
 // destination, imm8), e.g. VEXTRACTI64X4.
-func (e *enc) encodeEvexExtract(spec evexSpec, ops []Operand) error {
+func (e *enc) encodeEvexExtract(spec evexSpec, ops []Operand, mask int, zeroing bool) error {
 	if len(ops) != 3 {
 		return fmt.Errorf("extract expects 3 operands ($imm, zsrc, ydst), got %d", len(ops))
 	}
@@ -299,7 +504,7 @@ func (e *enc) encodeEvexExtract(spec evexSpec, ops []Operand) error {
 	if err != nil {
 		return err
 	}
-	if err := e.emitEvexFields(spec, srcReg.vecLenBit(), srcReg.idx, -1, dst); err != nil {
+	if err := e.emitEvexFields(spec, srcReg.vecLenBit(), srcReg.idx, -1, dst, mask, zeroing); err != nil {
 		return err
 	}
 	e.out = append(e.out, immByte)
@@ -309,7 +514,7 @@ func (e *enc) encodeEvexExtract(spec evexSpec, ops []Operand) error {
 // encodeEvexMove encodes a two-operand EVEX move; a vector→vector move uses
 // the store-form opcode (reg = source, rm = destination), matching the Go
 // assembler.
-func (e *enc) encodeEvexMove(mnem string, ms evexMoveSpec, ops []Operand) error {
+func (e *enc) encodeEvexMove(mnem string, ms evexMoveSpec, ops []Operand, mask int, zeroing bool) error {
 	if len(ops) != 2 {
 		return fmt.Errorf("EVEX move expects 2 operands, got %d", len(ops))
 	}
@@ -338,7 +543,47 @@ func (e *enc) encodeEvexMove(mnem string, ms evexMoveSpec, ops []Operand) error
 		return fmt.Errorf("%s needs a vector register operand", mnem)
 	}
 	spec := evexSpec{mapSel: ms.mapSel, opcode: op, w: ms.w, pp: ms.pp, opdigit: -1, n: ms.n}
-	return e.emitEvexFields(spec, reg.vecLenBit(), reg.idx, -1, rm)
+	return e.emitEvexFields(spec, reg.vecLenBit(), reg.idx, -1, rm, mask, zeroing)
+}
+
+// encodeEvexRMSrcLen encodes a length-narrowing conversion: OP src, dst with
+// the destination always XMM and the length fixed by the mnemonic — the
+// single valid slot of spec.n names the vector length (and the disp8×N
+// multiplier) a register or memory source encodes.
+func (e *enc) encodeEvexRMSrcLen(spec evexSpec, ops []Operand, mask int, zeroing bool) error {
+	if len(ops) != 2 {
+		return fmt.Errorf("conversion expects 2 operands, got %d", len(ops))
+	}
+	src, dst := ops[0], ops[1]
+	dstReg, ok := dst.(Reg)
+	if !ok || !dstReg.isVec() {
+		return fmt.Errorf("EVEX destination must be a vector register")
+	}
+	ll, err := soleLen(spec.n)
+	if err != nil {
+		return err
+	}
+	return e.emitEvexFields(spec, ll, dstReg.idx, -1, src, mask, zeroing)
+}
+
+// soleLen returns the vector-length index of the single valid slot of n —
+// the length a length-fixed mnemonic (the EVEX conversion spellings) encodes
+// regardless of its operands.
+func soleLen(n [3]int) (int, error) {
+	ll := -1
+	for i, v := range n {
+		if v == 0 {
+			continue
+		}
+		if ll >= 0 {
+			return 0, fmt.Errorf("ambiguous vector-length table %v", n)
+		}
+		ll = i
+	}
+	if ll < 0 {
+		return 0, fmt.Errorf("empty vector-length table")
+	}
+	return ll, nil
 }
 
 // memOperand reports whether op is a memory reference (including a
@@ -353,7 +598,7 @@ func memOperand(op Operand) bool {
 
 // encodeEvexRMRev encodes the narrowing-store form: OP src, dst with the wide
 // source in the reg field and the narrow destination in r/m (VPMOVDW/QD).
-func (e *enc) encodeEvexRMRev(spec evexSpec, ops []Operand) error {
+func (e *enc) encodeEvexRMRev(spec evexSpec, ops []Operand, mask int, zeroing bool) error {
 	if len(ops) != 2 {
 		return fmt.Errorf("EVEX store instruction expects 2 operands, got %d", len(ops))
 	}
@@ -362,12 +607,12 @@ func (e *enc) encodeEvexRMRev(spec evexSpec, ops []Operand) error {
 	if !ok || !srcReg.isVec() {
 		return fmt.Errorf("EVEX source must be a vector register")
 	}
-	return e.emitEvexFields(spec, srcReg.vecLenBit(), srcReg.idx, -1, dst)
+	return e.emitEvexFields(spec, srcReg.vecLenBit(), srcReg.idx, -1, dst, mask, zeroing)
 }
 
 // encodeEvexBcast encodes VPBROADCASTD/Q: OP src, dst with the GPR or memory
 // source broadcast to every lane of the vector destination.
-func (e *enc) encodeEvexBcast(bs evexBcastSpec, ops []Operand) error {
+func (e *enc) encodeEvexBcast(bs evexBcastSpec, ops []Operand, mask int, zeroing bool) error {
 	if len(ops) != 2 {
 		return fmt.Errorf("broadcast expects 2 operands, got %d", len(ops))
 	}
@@ -386,14 +631,15 @@ func (e *enc) encodeEvexBcast(bs evexBcastSpec, ops []Operand) error {
 	default:
 		return fmt.Errorf("broadcast source must be a register or memory")
 	}
-	return e.emitEvexFields(spec, dstReg.vecLenBit(), dstReg.idx, -1, src)
+	return e.emitEvexFields(spec, dstReg.vecLenBit(), dstReg.idx, -1, src, mask, zeroing)
 }
 
 // emitEvexFields emits the EVEX prefix, opcode, ModR/M, SIB and displacement
 // (disp8×N compressed) for the given precomputed fields.  regIdx is the
 // unextended reg-field register index, or a /digit (0–7); vvvvIdx is the
-// vvvv register index, or -1 when unused.
-func (e *enc) emitEvexFields(spec evexSpec, ll, regIdx, vvvvIdx int, rm Operand) error {
+// vvvv register index, or -1 when unused.  mask (K1–K7, 0 = unmasked) and
+// zeroing fill the aaa and z bits of the P2 byte.
+func (e *enc) emitEvexFields(spec evexSpec, ll, regIdx, vvvvIdx int, rm Operand, mask int, zeroing bool) error {
 	if ll > 2 {
 		return fmt.Errorf("invalid vector length")
 	}
@@ -420,7 +666,8 @@ func (e *enc) emitEvexFields(spec evexSpec, ll, regIdx, vvvvIdx int, rm Operand)
 	var sb *sbRef
 	switch r := rm.(type) {
 	case Reg:
-		// ModRM.mod = 11: rm[3] extends via B̄, rm[4] via X̄.
+		// ModRM.mod = 11: rm[3] extends via B̄, and rm[4] via X̄ (the EVEX
+		// register-register quirk).
 		modrm = 0xC0 | (regIdx&7)<<3 | (r.idx & 7)
 		sib = -1
 		if r.idx&8 != 0 {
@@ -429,6 +676,9 @@ func (e *enc) emitEvexFields(spec evexSpec, ll, regIdx, vvvvIdx int, rm Operand)
 		if r.idx&16 != 0 {
 			xBar = 0
 		}
+		if r.idx&16 != 0 {
+			xBar = 0
+		}
 	case Mem:
 		var err error
 		modrm, sib, disp, xBar, bBar, err = memComponentsEvex(regIdx&7, r, spec.n[ll])
@@ -451,9 +701,13 @@ func (e *enc) emitEvexFields(spec evexSpec, ll, regIdx, vvvvIdx int, rm Operand)
 		return fmt.Errorf("invalid EVEX r/m operand")
 	}
 
+	z := 0
+	if zeroing {
+		z = 1
+	}
 	p0 := byte(rBar<<7 | xBar<<6 | bBar<<5 | rPrimeBar<<4 | spec.mapSel)
 	p1 := byte(spec.w<<7 | vBar<<3 | 1<<2 | spec.pp)
-	p2 := byte(ll<<5 | vPrimeBar<<3) // z = 0, b = 0, aaa = 0
+	p2 := byte(z<<7 | ll<<5 | vPrimeBar<<3 | mask) // z, L'L, b=0, V', aaa
 	e.out = append(e.out, 0x62, p0, p1, p2, spec.opcode, byte(modrm))
 	if sib >= 0 {
 		e.out = append(e.out, byte(sib))

asm/evex_test.go

@@ -65,6 +65,23 @@ func TestEvexGroundTruth(t *testing.T) {
 		{"VMOVDQU64 (SI)(R15*4),Z3", "VMOVDQU64", []Operand{Idx(SI, vreg(t, "R15"), 4, 0, 64), vreg(t, "Z3")}, "62b1fe486f1cbe"},
 		{"VMOVDQU64 Z0,4(SI)(AX*1)", "VMOVDQU64", []Operand{vreg(t, "Z0"), Idx(SI, AX, 1, 4, 64)}, "62f1fe487f840604000000"},
 		{"VMOVDQU64 Z1,Z2", "VMOVDQU64", []Operand{vreg(t, "Z1"), vreg(t, "Z2")}, "62f1fe487fca"},
+		// The wider AVX-512 F/BW integer set.
+		{"VPADDB Z1,Z2,Z3", "VPADDB", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f16d48fcd9"},
+		{"VPSUBW Z1,Z2,Z3", "VPSUBW", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f16d48f9d9"},
+		{"VPANDQ Z1,Z2,Z3", "VPANDQ", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f1ed48dbd9"},
+		{"VPANDND Z1,Z2,Z3", "VPANDND", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f16d48dfd9"},
+		{"VPMULLW Z1,Z2,Z3", "VPMULLW", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f16d48d5d9"},
+		{"VPMINUB Z1,Z2,Z3", "VPMINUB", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f16d48dad9"},
+		{"VPMAXUQ Z1,Z2,Z3", "VPMAXUQ", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f2ed483fd9"},
+		{"VPAVGW Z1,Z2,Z3", "VPAVGW", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f16d48e3d9"},
+		{"VPSLLVQ Z3,Z1,Z2", "VPSLLVQ", []Operand{vreg(t, "Z3"), vreg(t, "Z1"), vreg(t, "Z2")}, "62f2f54847d3"},
+		{"VPSRAVQ Z3,Z1,Z2", "VPSRAVQ", []Operand{vreg(t, "Z3"), vreg(t, "Z1"), vreg(t, "Z2")}, "62f2f54846d3"},
+		{"VPSHUFD $0x1B,Z1,Z2", "VPSHUFD", []Operand{Imm(0x1B), vreg(t, "Z1"), vreg(t, "Z2")}, "62f17d4870d11b"},
+		{"VPSHUFB Z1,Z2,Z3", "VPSHUFB", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f26d4800d9"},
+		{"VMOVDQU8 Z1,Z2", "VMOVDQU8", []Operand{vreg(t, "Z1"), vreg(t, "Z2")}, "62f17f487fca"},
+		{"VMOVDQU16 Z1,Z2", "VMOVDQU16", []Operand{vreg(t, "Z1"), vreg(t, "Z2")}, "62f1ff487fca"},
+		// Indices 16–31: rm[4] rides in X̄ for register operands.
+		{"VPSHUFD $1,X16,X17", "VPSHUFD", []Operand{Imm(1), vreg(t, "X16"), vreg(t, "X17")}, "62a17d0870c801"},
 		{"VMOVUPD (DI),Z14", "VMOVUPD", []Operand{Ptr(DI, 0, 64), vreg(t, "Z14")}, "6271fd481037"},
 		{"VMOVUPD 64(DI),Z14", "VMOVUPD", []Operand{Ptr(DI, 64, 64), vreg(t, "Z14")}, "6271fd48107701"},
 		// Conversions and narrowing stores (reg = wide source).
@@ -84,6 +101,32 @@ func TestEvexGroundTruth(t *testing.T) {
 		{"VPBROADCASTQ AX,Z9", "VPBROADCASTQ", []Operand{AX, vreg(t, "Z9")}, "6272fd487cc8"},
 		// Register indices 16–31 exist only in EVEX encodings.
 		{"VPBROADCASTD AX,Y30", "VPBROADCASTD", []Operand{AX, vreg(t, "Y30")}, "62627d287cf0"},
+		// Packed double arithmetic / unpack (EVEX forms carry W=1).
+		{"VSUBPD Z1,Z2,Z3", "VSUBPD", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f1ed485cd9"},
+		{"VDIVPD Z4,Z5,Z6", "VDIVPD", []Operand{vreg(t, "Z4"), vreg(t, "Z5"), vreg(t, "Z6")}, "62f1d5485ef4"},
+		{"VMINPD Z7,Z8,Z9", "VMINPD", []Operand{vreg(t, "Z7"), vreg(t, "Z8"), vreg(t, "Z9")}, "6271bd485dcf"},
+		{"VMAXPD Z10,Z11,Z12", "VMAXPD", []Operand{vreg(t, "Z10"), vreg(t, "Z11"), vreg(t, "Z12")}, "6251a5485fe2"},
+		{"VUNPCKLPD Z1,Z2,Z3", "VUNPCKLPD", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f1ed4814d9"},
+		{"VUNPCKHPD Z1,Z2,Z3", "VUNPCKHPD", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}, "62f1ed4815d9"},
+		{"VSUBPD 64(AX),Z1,Z2", "VSUBPD", []Operand{Ptr(AX, 64, 64), vreg(t, "Z1"), vreg(t, "Z2")}, "62f1f5485c5001"},
+		{"VSUBPD Z17,Z18,Z19", "VSUBPD", []Operand{vreg(t, "Z17"), vreg(t, "Z18"), vreg(t, "Z19")}, "62a1ed405cd9"},
+		// VMOVDDUP — duplicate the low double; disp8×N = 64 at 512 bits, and
+		// X16/X17 force EVEX (the mod=11 rm[4] extension rides in X̄).
+		{"VMOVDDUP Z1,Z2", "VMOVDDUP", []Operand{vreg(t, "Z1"), vreg(t, "Z2")}, "62f1ff4812d1"},
+		{"VMOVDDUP 64(AX),Z1", "VMOVDDUP", []Operand{Ptr(AX, 64, 64), vreg(t, "Z1")}, "62f1ff48124801"},
+		{"VMOVDDUP X16,X17", "VMOVDDUP", []Operand{vreg(t, "X16"), vreg(t, "X17")}, "62a1ff0812c8"},
+		// Conversions: DQ→PS, PS→PD (pp = 00, the Go assembler's choice),
+		// DQ→PD (the destination sets the length).
+		{"VCVTDQ2PS Z1,Z2", "VCVTDQ2PS", []Operand{vreg(t, "Z1"), vreg(t, "Z2")}, "62f17c485bd1"},
+		{"VCVTPS2PD Y1,Z2", "VCVTPS2PD", []Operand{vreg(t, "Y1"), vreg(t, "Z2")}, "62f17c485ad1"},
+		{"VCVTPS2PD 32(AX),Z2", "VCVTPS2PD", []Operand{Ptr(AX, 32, 32), vreg(t, "Z2")}, "62f17c485a5001"},
+		{"VCVTDQ2PD Y1,Z2", "VCVTDQ2PD", []Operand{vreg(t, "Y1"), vreg(t, "Z2")}, "62f17e48e6d1"},
+		// PD→DQ conversions: the source is the wide operand and fixes the
+		// length (ZMM source → L'L = 10 even with an XMM destination; a
+		// memory source takes the length the mnemonic's spelling implies).
+		{"VCVTPD2DQ Z1,Y2", "VCVTPD2DQ", []Operand{vreg(t, "Z1"), vreg(t, "Y2")}, "62f1ff48e6d1"},
+		{"VCVTPD2DQ 64(AX),Y2", "VCVTPD2DQ", []Operand{Ptr(AX, 64, 64), vreg(t, "Y2")}, "62f1ff48e65001"},
+		{"VCVTTPD2DQ Z3,Y4", "VCVTTPD2DQ", []Operand{vreg(t, "Z3"), vreg(t, "Y4")}, "62f1fd48e6e3"},
 	}
 	for _, c := range cases {
 		want := strings.ReplaceAll(c.want, " ", "")
@@ -110,6 +153,93 @@ func TestEvexGroundTruth(t *testing.T) {
 	}
 }
 
+// TestEvexMasking checks the AVX-512 mask operand (K1–K7, placed freely among
+// the operands) and the .Z zeroing suffix, byte for byte against the Go
+// assembler.
+func TestEvexMasking(t *testing.T) {
+	cases := []struct {
+		name string
+		mnem string
+		ops  []Operand
+		want string
+	}{
+		// Masked arithmetic: K anywhere among the operands; .Z sets the z bit.
+		{"VPADDD.Z merging+zeroing", "VPADDD.Z", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "K2"), vreg(t, "Z3")}, "62f16dcafed9"},
+		{"VPADDD merging", "VPADDD", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "K1"), vreg(t, "Z3")}, "62f16d49fed9"},
+		{"VADDPD.Z", "VADDPD.Z", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "K2"), vreg(t, "Z3")}, "62f1edca58d9"},
+		{"VPMINSD.Z", "VPMINSD.Z", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "K5"), vreg(t, "Z3")}, "62f26dcd39d9"},
+		{"VPMINSQ.Z", "VPMINSQ.Z", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "K5"), vreg(t, "Z3")}, "62f2edcd39d9"},
+		// Masked immediate shift (K before the destination).
+		{"VPSRAD.Z", "VPSRAD.Z", []Operand{Imm(1), vreg(t, "Z2"), vreg(t, "K1"), vreg(t, "Z3")}, "62f165c972e201"},
+		{"VPSLLD merge", "VPSLLD", []Operand{Imm(4), vreg(t, "Z1"), vreg(t, "K2"), vreg(t, "Z3")}, "62f1654a72f104"},
+		// Masked align.
+		{"VALIGND", "VALIGND", []Operand{Imm(12), vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "K3"), vreg(t, "Z4")}, "62f36d4b03e10c"},
+		// Masked conversion and extract.
+		{"VCVTQQ2PD.Z", "VCVTQQ2PD.Z", []Operand{vreg(t, "Z1"), vreg(t, "K2"), vreg(t, "Z3")}, "62f1fecae6d9"},
+		{"VEXTRACTI64X4", "VEXTRACTI64X4", []Operand{Imm(1), vreg(t, "Z1"), vreg(t, "K2"), vreg(t, "Y3")}, "62f3fd4a3bcb01"},
+		// Masked moves: K sits between the register and memory operands.
+		{"VMOVDQU8 store", "VMOVDQU8", []Operand{vreg(t, "Z1"), vreg(t, "K3"), Ptr(SI, 0, 64)}, "62f17f4b7f0e"},
+		{"VMOVDQU32 load", "VMOVDQU32", []Operand{Ptr(SI, 0, 64), vreg(t, "K4"), vreg(t, "Z1")}, "62f17e4c6f0e"},
+		{"VMOVDQU32 store", "VMOVDQU32", []Operand{vreg(t, "Z1"), vreg(t, "K4"), Ptr(DI, 0, 64)}, "62f17e4c7f0f"},
+		// Masked comparison with a K destination: dst K1, mask K2.
+		{"VPCMPEQD k-dst+mask", "VPCMPEQD", []Operand{vreg(t, "Z0"), vreg(t, "Z3"), vreg(t, "K2"), vreg(t, "K1")}, "62f1654a76c8"},
+		// Masked floating point: packed double, the scalar SD/SS forms (which
+		// exist under EVEX only for masked and zeroing use) and conversions.
+		{"VSUBPD.Z", "VSUBPD.Z", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "K3"), vreg(t, "Z4")}, "62f1edcb5ce1"},
+		{"VADDSD merge", "VADDSD", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "K3"), vreg(t, "X4")}, "62f1ef0b58e1"},
+		{"VSUBSD.Z", "VSUBSD.Z", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "K5"), vreg(t, "X3")}, "62f1ef8d5cd9"},
+		{"VADDSS merge", "VADDSS", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "K1"), vreg(t, "X3")}, "62f16e0958d9"},
+		{"VCVTPD2DQ merge", "VCVTPD2DQ", []Operand{vreg(t, "Z1"), vreg(t, "K2"), vreg(t, "Y3")}, "62f1ff4ae6d9"},
+		{"VCVTTPD2DQ.Z", "VCVTTPD2DQ.Z", []Operand{vreg(t, "Z1"), vreg(t, "K2"), vreg(t, "Y3")}, "62f1fdcae6d9"},
+		{"VCVTDQ2PS.Z", "VCVTDQ2PS.Z", []Operand{vreg(t, "Z1"), vreg(t, "K4"), vreg(t, "Z2")}, "62f17ccc5bd1"},
+		{"VCVTDQ2PD merge", "VCVTDQ2PD", []Operand{vreg(t, "X1"), vreg(t, "K2"), vreg(t, "X3")}, "62f17e0ae6d9"},
+		{"VCVTDQ2PD.Z", "VCVTDQ2PD.Z", []Operand{vreg(t, "Y1"), vreg(t, "K2"), vreg(t, "Z2")}, "62f17ecae6d1"},
+		{"VCVTPS2PD.Z", "VCVTPS2PD.Z", []Operand{vreg(t, "Y1"), vreg(t, "K3"), vreg(t, "Z2")}, "62f17ccb5ad1"},
+	}
+	for _, c := range cases {
+		code, err := Encode(c.mnem, c.ops...)
+		if err != nil {
+			t.Errorf("%s: Encode: %v", c.name, err)
+			continue
+		}
+		if got := hexCompact(code); got != c.want {
+			t.Errorf("%s: bytes %s, want %s", c.name, got, c.want)
+			continue
+		}
+		inst, err := x86asm.Decode(code, 64)
+		if err != nil {
+			t.Errorf("%s: Decode(%x): %v", c.name, code, err)
+			continue
+		}
+		want := c.mnem
+		if i := len(want) - 2; i > 0 && want[i:] == ".Z" {
+			want = want[:i]
+		}
+		if inst.Op.String() != want {
+			t.Errorf("%s: decoded as %s", c.name, inst.Op.String())
+		}
+	}
+
+	// Error cases.
+	bad := []struct {
+		name string
+		mnem string
+		ops  []Operand
+	}{
+		{"zeroing without mask", "VPADDD.Z", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}},
+		{"K0 mask", "VPADDD", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "K0"), vreg(t, "Z3")}},
+		{"two masks", "VPADDD", []Operand{vreg(t, "Z1"), vreg(t, "K1"), vreg(t, "K2"), vreg(t, "Z3")}},
+		{".Z on VEX-only", "VPSHUFD.Z", []Operand{Imm(1), vreg(t, "X0"), vreg(t, "X1")}},
+		{"unsupported suffix", "VPADDD.BCST", []Operand{vreg(t, "Z1"), vreg(t, "Z2"), vreg(t, "Z3")}},
+		{"KMOVW.Z", "KMOVW.Z", []Operand{vreg(t, "K1"), vreg(t, "K2")}},
+	}
+	for _, c := range bad {
+		if _, err := Encode(c.mnem, c.ops...); err == nil {
+			t.Errorf("%s: expected an error, got none", c.name)
+		}
+	}
+}
+
 // TestEvexErrors checks the EVEX-specific error paths.
 func TestEvexErrors(t *testing.T) {
 	cases := []struct {
@@ -125,7 +255,7 @@ func TestEvexErrors(t *testing.T) {
 		{"VPMOVDW src", "VPMOVDW", []Operand{AX, vreg(t, "Y0")}},
 		{"align arity", "VALIGND", []Operand{Imm(1), vreg(t, "Z0"), vreg(t, "Z1")}},
 		// VEX-only mnemonics reject registers only EVEX can encode.
-		{"VPSHUFD X16", "VPSHUFD", []Operand{Imm(1), vreg(t, "X16"), vreg(t, "X17")}},
+		{"VMOVMSKPS X16", "VMOVMSKPS", []Operand{vreg(t, "X16"), AX}},
 	}
 	for _, c := range cases {
 		if _, err := Encode(c.mnem, c.ops...); err == nil {

asm/link.go

@@ -5,27 +5,58 @@ package asm
 
 import (
 	"fmt"
+	"sort"
 
 	"sourcedock.dev/petrbalvin/gasm-devkit/ast"
 )
 
 // Image is an assembled file: the function bodies laid out in source order,
-// followed by the file's static data section (GLOBL/DATA).  Static-symbol
-// references are encoded RIP-relative and resolved within the image, so the
-// bytes are self-consistent and executable at any base address.
+// followed by the file's static data section (GLOBL/DATA).  References to
+// file-local static symbols are encoded RIP-relative and resolved within the
+// image, so the raw bytes are self-consistent and executable at any base
+// address; references to external symbols are recorded as relocations
+// (Funcs[i].Relocs, Externals) and left unresolved — the object-file
+// emitters turn them into linker relocations.
 type Image struct {
 	Code      []byte         // concatenated function bodies
 	Data      []byte         // static data section
 	Funcs     []FuncLayout   // function positions, in source order
 	Symbols   map[string]int // static symbol → byte offset within the image
+	DataSyms  []DataSymbol   // GLOBL symbols, in layout order
+	Externals []string       // referenced but undefined symbols, sorted
 }
 
 // FuncLayout describes one assembled function within an Image.
 type FuncLayout struct {
 	Name   string
+	Pkg    string // explicit package prefix ("" = the current package)
+	Static bool   // the <> marker: file-local, not exported
 	Offset int    // start offset within the image (== offset within Code)
 	Size   int
 	Labels map[string]int // local labels, function-relative
+	Relocs []Reloc        // static-symbol references, in emission order
+}
+
+// Reloc is one static-symbol reference within a function body: the disp32
+// field at Off (function-relative) must reach the symbol plus Addend,
+// measured from After, the address just past the instruction.  An External
+// relocation names a symbol no GLOBL in the file defines; the object-file
+// emitters carry it into the output's relocation table.
+type Reloc struct {
+	Off      int
+	After    int
+	Name     string
+	Addend   int64
+	External bool
+}
+
+// DataSymbol describes one GLOBL symbol laid out in the data section.
+type DataSymbol struct {
+	Name   string
+	Pkg    string // explicit package prefix ("" = the current package)
+	Offset int    // byte offset within Data
+	Size   int
+	Static bool // the <> marker: file-local, not exported
 }
 
 // Bytes returns the whole image: code, then data.
@@ -37,19 +68,21 @@ func (img *Image) Bytes() []byte {
 
 // AssembleFile assembles every TEXT function of a parsed file and lays out
 // its static symbols (GLOBL/DATA) in a data section behind the code.  Each
-// static-symbol reference becomes a RIP-relative load whose displacement is
-// resolved against that layout.  External (non-file-local) symbol references
-// are rejected: they need object-file emission.
+// reference to a file-local static symbol becomes a RIP-relative load whose
+// displacement is resolved against that layout; a reference to a symbol no
+// GLOBL defines is recorded as an external relocation (Externals) with its
+// displacement left zero — the object-file emitters resolve it at link
+// time, while the raw image (Bytes) cannot represent it.
 func AssembleFile(f *ast.File) (*Image, error) {
-	syms, order, err := collectData(f)
+	dataSyms, err := collectData(f)
 	if err != nil {
 		return nil, err
 	}
-	known := make(map[string]bool, len(syms))
-	for name := range syms {
-		known[name] = true
+	known := make(map[string]bool, len(dataSyms))
+	for _, d := range dataSyms {
+		known[d.name] = true
 	}
-	link := &linkInfo{symbols: known}
+	link := &linkInfo{symbols: known, allowExternal: true}
 
 	img := &Image{Symbols: map[string]int{}}
 	type asmFunc struct {
@@ -68,6 +101,8 @@ func AssembleFile(f *ast.File) (*Image, error) {
 		}
 		img.Funcs = append(img.Funcs, FuncLayout{
 			Name:   t.Name.Name,
+			Pkg:    t.Name.Pkg,
+			Static: t.Name.Static,
 			Offset: len(img.Code),
 			Size:   len(code),
 			Labels: labels,
@@ -78,34 +113,63 @@ func AssembleFile(f *ast.File) (*Image, error) {
 
 	// Lay out the data section behind the code, each symbol 16-aligned.
 	dataStart := len(img.Code)
-	for _, name := range order {
+	for _, d := range dataSyms {
 		if pos := dataStart + len(img.Data); pos != align16(pos) {
 			img.Data = append(img.Data, make([]byte, align16(pos)-pos)...)
 		}
-		img.Symbols[name] = dataStart + len(img.Data)
-		img.Data = append(img.Data, syms[name]...)
+		img.Symbols[d.name] = dataStart + len(img.Data)
+		img.DataSyms = append(img.DataSyms, DataSymbol{
+			Name:   d.name,
+			Pkg:    d.pkg,
+			Offset: len(img.Data),
+			Size:   len(d.buf),
+			Static: d.static,
+		})
+		img.Data = append(img.Data, d.buf...)
 	}
 
-	// Resolve the RIP-relative displacements now that every address is known.
+	// Resolve the RIP-relative displacements of file-local references now
+	// that every address is known, and record every reference (resolved or
+	// external) for the object-file emitters.
+	externals := map[string]bool{}
 	for i, fn := range funcs {
 		base := img.Funcs[i].Offset
 		code := img.Code[base : base+img.Funcs[i].Size]
 		for _, p := range fn.patches {
-			rel := int64(img.Symbols[p.name]) + p.addend - int64(base+p.after)
+			reloc := Reloc{Off: p.off, After: p.after, Name: p.name, Addend: p.addend}
+			if imgOff, ok := img.Symbols[p.name]; ok {
+				rel := int64(imgOff) + p.addend - int64(base+p.after)
 				if rel < -1<<31 || rel >= 1<<31 {
 					return nil, fmt.Errorf("%s: displacement to %q out of rel32 range", fn.name, p.name)
 				}
 				copy(code[p.off:p.off+4], le32(rel))
+			} else {
+				reloc.External = true
+				externals[p.name] = true
+			}
+			img.Funcs[i].Relocs = append(img.Funcs[i].Relocs, reloc)
 		}
 	}
+	for name := range externals {
+		img.Externals = append(img.Externals, name)
+	}
+	sort.Strings(img.Externals)
 	return img, nil
 }
 
+// dataSym is one GLOBL symbol and its DATA initialiser.
+type dataSym struct {
+	name   string
+	pkg    string
+	buf    []byte
+	static bool
+}
+
 // collectData gathers the file's static symbols (GLOBL) and their initial
 // contents (DATA) into byte buffers, in declaration order.
-func collectData(f *ast.File) (map[string][]byte, []string, error) {
-	syms := map[string][]byte{}
-	var order []string
+func collectData(f *ast.File) ([]dataSym, error) {
+	index := map[string]int{}
+	var syms []dataSym
 	for _, d := range f.Decls {
 		switch dd := d.(type) {
 		case *ast.Globl:
@@ -113,47 +177,53 @@ func collectData(f *ast.File) (map[string][]byte, []string, error) {
 				continue
 			}
 			name := dd.Name.Name
-			if _, dup := syms[name]; dup {
-				return nil, nil, fmt.Errorf("duplicate GLOBL %q", name)
+			if _, dup := index[name]; dup {
+				return nil, fmt.Errorf("duplicate GLOBL %q", name)
 			}
 			size := 0
 			if dd.Size != nil && dd.Size.Imm.HasVal {
 				size = int(dd.Size.Imm.Val)
 			}
-			syms[name] = make([]byte, size)
-			order = append(order, name)
+			index[name] = len(syms)
+			syms = append(syms, dataSym{
+				name:   name,
+				pkg:    dd.Name.Pkg,
+				buf:    make([]byte, size),
+				static: dd.Name.Static,
+			})
 
 		case *ast.Data:
 			if dd.Name == nil || dd.Name.Pseudo != "SB" {
 				continue
 			}
-			buf, ok := syms[dd.Name.Name]
+			i, ok := index[dd.Name.Name]
 			if !ok {
-				return nil, nil, fmt.Errorf("DATA %q: no matching GLOBL", dd.Name.Name)
+				return nil, fmt.Errorf("DATA %q: no matching GLOBL", dd.Name.Name)
 			}
 			if dd.Value == nil || !dd.Value.Imm.HasVal {
-				return nil, nil, fmt.Errorf("DATA %q: value must be an integer immediate", dd.Name.Name)
+				return nil, fmt.Errorf("DATA %q: value must be an integer immediate", dd.Name.Name)
 			}
 			w := dd.Width
 			switch w {
 			case 1, 2, 4, 8:
 			default:
-				return nil, nil, fmt.Errorf("DATA %q: invalid width %d (want 1, 2, 4 or 8)", dd.Name.Name, w)
+				return nil, fmt.Errorf("DATA %q: invalid width %d (want 1, 2, 4 or 8)", dd.Name.Name, w)
 			}
 			off := dd.Name.Offset
+			buf := syms[i].buf
 			if off < 0 || off+int64(w) > int64(len(buf)) {
-				return nil, nil, fmt.Errorf("DATA %q+%d/%d exceeds GLOBL size %d", dd.Name.Name, off, w, len(buf))
+				return nil, fmt.Errorf("DATA %q+%d/%d exceeds GLOBL size %d", dd.Name.Name, off, w, len(buf))
 			}
 			v := dd.Value.Imm.Val
 			if dd.Value.Imm.Neg {
 				v = -v
 			}
-			for i := 0; i < w; i++ {
-				buf[off+int64(i)] = byte(v >> (8 * i))
+			for j := 0; j < w; j++ {
+				buf[off+int64(j)] = byte(v >> (8 * j))
 			}
 		}
 	}
-	return syms, order, nil
+	return syms, nil
 }
 
 // align16 rounds n up to the next multiple of 16.

asm/macho.go

@@ -0,0 +1,258 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+package asm
+
+import (
+	"encoding/binary"
+	"fmt"
+)
+
+// This file emits Mach-O x86-64 objects (MH_OBJECT) from an assembled
+// Image, in the shape the Darwin assembler produces: one unnamed segment
+// carrying a __TEXT,__text and a __DATA,__data section laid out back to
+// back at addresses zero and len(code), a symbol table (locals first, then
+// exported definitions, then undefined externals) and one relocation entry
+// per static-symbol reference, of type X86_64_RELOC_SIGNED.
+//
+// The image's own address space carries straight over — the data section
+// starts immediately after the code, and the layout padding already lives
+// inside Image.Data — so every symbol keeps its image address as its
+// n_value, and a local (non-external) relocation leaves the displacement
+// the assembler resolved in place: the linker only adjusts it by the
+// section's final movement.
+
+// Mach-O constants.
+const (
+	machoMagic64   = 0xfeedfacf
+	machoCPUamd64  = 0x01000007 // CPU_TYPE_X86_64
+	machoCPUSubAll = 3          // CPU_SUBTYPE_X86_64_ALL
+	machoObj       = 1          // MH_OBJECT
+
+	machoSegment64 = 0x19 // LC_SEGMENT_64
+	machoSymtab    = 0x2  // LC_SYMTAB
+
+	machoSectTextFlags = 0x80000400 // S_ATTR_PURE_INSTRUCTIONS | S_ATTR_SOME_INSTRUCTIONS
+
+	nUndf = 0x00 // undefined symbol
+	nSect = 0x0e // defined in section number n_sect
+	nExt  = 0x01 // external (exported or undefined-global) bit
+
+	x8664RelocSigned = 1
+)
+
+// MachOObject returns the image as a Mach-O x86-64 relocatable object
+// (MH_OBJECT), the shape the Darwin toolchain links.  Symbol names follow
+// the same rules as the ELF output.  Every static-symbol reference becomes
+// an X86_64_RELOC_SIGNED relocation: external references against their
+// undefined symbol, file-local ones against the __DATA section with the
+// resolved displacement carried in the instruction bytes.
+func (img *Image) MachOObject() ([]byte, error) {
+	le := binary.LittleEndian
+
+	// Section ordinals (1-based, as Mach-O numbers them).
+	const (
+		sectText = 1
+		sectData = 2
+	)
+
+	// Object address space: code at 0, data immediately after (the layout
+	// padding is already part of img.Data, so image addresses are object
+	// addresses).
+	textAddr := uint64(0)
+	dataAddr := uint64(len(img.Code))
+	vmsize := dataAddr + uint64(len(img.Data))
+
+	// The code, with external displacements primed to addend − 4: the
+	// linker adds the symbol's address to the field as it stands.  Local
+	// displacements stay as the assembler resolved them.
+	code := append([]byte(nil), img.Code...)
+	for _, fn := range img.Funcs {
+		for _, r := range fn.Relocs {
+			if r.External {
+				// Prime the field to the addend measured from the patch
+				// site: the assembler records it from the instruction end,
+				// After − Off bytes past the field.
+				copy(code[fn.Offset+r.Off:], le32(r.Addend-int64(r.After-r.Off)))
+			}
+		}
+	}
+
+	// Symbols: locals first, then exported definitions, then undefined
+	// externals — the order the classic link editor expects.
+	type machoSym struct {
+		name  string
+		typ   byte
+		sect  byte
+		value uint64
+	}
+	var locals, globals, undefs []machoSym
+	for _, fn := range img.Funcs {
+		s := machoSym{name: objectName(fn.Pkg, fn.Name), typ: nSect, sect: sectText, value: textAddr + uint64(fn.Offset)}
+		if fn.Static {
+			locals = append(locals, s)
+		} else {
+			s.typ |= nExt
+			globals = append(globals, s)
+		}
+	}
+	for _, d := range img.DataSyms {
+		s := machoSym{name: objectName(d.Pkg, d.Name), typ: nSect, sect: sectData, value: dataAddr + uint64(d.Offset)}
+		if d.Static {
+			locals = append(locals, s)
+		} else {
+			s.typ |= nExt
+			globals = append(globals, s)
+		}
+	}
+	for _, name := range img.Externals {
+		undefs = append(undefs, machoSym{name: name, typ: nUndf | nExt})
+	}
+	syms := append(append(locals, globals...), undefs...)
+	symIdx := map[string]int{}
+	for i, s := range syms {
+		symIdx[s.name] = i
+	}
+
+	// Relocations, attached to the __text section.
+	type machoReloc struct {
+		addr   uint32
+		symnum uint32
+		extern bool
+	}
+	var relocs []machoReloc
+	for _, fn := range img.Funcs {
+		for _, r := range fn.Relocs {
+			rel := machoReloc{addr: uint32(fn.Offset + r.Off)}
+			if r.External {
+				idx, ok := symIdx[r.Name]
+				if !ok {
+					return nil, fmt.Errorf("relocation references unknown symbol %q", r.Name)
+				}
+				rel.symnum = uint32(idx)
+				rel.extern = true
+			} else {
+				// Section-relative: r_symbolnum carries the section number
+				// and the resolved displacement stays in the bytes.
+				rel.symnum = sectData
+			}
+			relocs = append(relocs, rel)
+		}
+	}
+
+	// The string table opens with the conventional " \0".
+	strtab := []byte{' ', 0}
+	strOff := map[string]int{}
+	for _, s := range syms {
+		if _, ok := strOff[s.name]; ok {
+			continue
+		}
+		strOff[s.name] = len(strtab)
+		strtab = append(strtab, s.name...)
+		strtab = append(strtab, 0)
+	}
+
+	// File layout: header, the two load commands, section data (code,
+	// data), the relocation table, the symbol table, the string table.
+	const (
+		hdrSize    = 32
+		segCmdSize = 72 + 2*80 // segment command with two sections
+		symCmdSize = 24
+	)
+	sizeofcmds := segCmdSize + symCmdSize
+	dataOff := hdrSize + sizeofcmds
+	reloff := dataOff + len(code) + len(img.Data)
+	symoff := reloff + 8*len(relocs)
+	stroff := symoff + 16*len(syms)
+
+	out := make([]byte, stroff+len(strtab))
+
+	// mach_header_64.
+	le.PutUint32(out[0:], machoMagic64)
+	le.PutUint32(out[4:], machoCPUamd64)
+	le.PutUint32(out[8:], machoCPUSubAll)
+	le.PutUint32(out[12:], machoObj)
+	le.PutUint32(out[16:], 2) // ncmds
+	le.PutUint32(out[20:], uint32(sizeofcmds))
+	le.PutUint32(out[24:], 0) // flags
+	le.PutUint32(out[28:], 0) // reserved
+
+	// LC_SEGMENT_64 with the two sections.
+	p := hdrSize
+	le.PutUint32(out[p:], machoSegment64)
+	le.PutUint32(out[p+4:], segCmdSize)
+	// segname: the empty string, zero-padded to 16 bytes.
+	le.PutUint64(out[p+8:], 0)
+	le.PutUint64(out[p+16:], 0)
+	le.PutUint64(out[p+24:], 0) // vmaddr
+	le.PutUint64(out[p+32:], vmsize)
+	le.PutUint64(out[p+40:], uint64(dataOff))
+	le.PutUint64(out[p+48:], vmsize)
+	le.PutUint32(out[p+56:], 7) // maxprot rwx
+	le.PutUint32(out[p+60:], 7) // initprot rwx
+	le.PutUint32(out[p+64:], 2) // nsects
+	le.PutUint32(out[p+68:], 0) // flags
+
+	// __TEXT,__text
+	s := p + 72
+	copy(out[s:], "__text")
+	copy(out[s+16:], "__TEXT")
+	le.PutUint64(out[s+32:], textAddr)
+	le.PutUint64(out[s+40:], uint64(len(code)))
+	le.PutUint32(out[s+48:], uint32(dataOff))
+	le.PutUint32(out[s+52:], 4) // align 2^4
+	le.PutUint32(out[s+56:], uint32(reloff))
+	le.PutUint32(out[s+60:], uint32(len(relocs)))
+	le.PutUint32(out[s+64:], machoSectTextFlags)
+
+	// __DATA,__data
+	s += 80
+	copy(out[s:], "__data")
+	copy(out[s+16:], "__DATA")
+	le.PutUint64(out[s+32:], dataAddr)
+	le.PutUint64(out[s+40:], uint64(len(img.Data)))
+	le.PutUint32(out[s+48:], uint32(dataOff+len(code)))
+	le.PutUint32(out[s+52:], 4) // align 2^4
+
+	// LC_SYMTAB.
+	p = hdrSize + segCmdSize
+	le.PutUint32(out[p:], machoSymtab)
+	le.PutUint32(out[p+4:], symCmdSize)
+	le.PutUint32(out[p+8:], uint32(symoff))
+	le.PutUint32(out[p+12:], uint32(len(syms)))
+	le.PutUint32(out[p+16:], uint32(stroff))
+	le.PutUint32(out[p+20:], uint32(len(strtab)))
+
+	// Section data.
+	copy(out[dataOff:], code)
+	copy(out[dataOff+len(code):], img.Data)
+
+	// Relocation entries.
+	for i, r := range relocs {
+		e := out[reloff+i*8:]
+		le.PutUint32(e[0:], r.addr)
+		bits := r.symnum & 0x00ffffff
+		bits |= 1 << 24 // r_pcrel
+		bits |= 2 << 25 // r_length = 4 bytes
+		if r.extern {
+			bits |= 1 << 27 // r_extern
+		}
+		bits |= x8664RelocSigned << 28
+		le.PutUint32(e[4:], bits)
+	}
+
+	// nlist_64 entries.
+	for i, s := range syms {
+		e := out[symoff+i*16:]
+		le.PutUint32(e[0:], uint32(strOff[s.name]))
+		e[4] = s.typ
+		e[5] = s.sect
+		le.PutUint16(e[6:], 0) // n_desc
+		le.PutUint64(e[8:], s.value)
+	}
+
+	// String table.
+	copy(out[stroff:], strtab)
+
+	return out, nil
+}

asm/macho_test.go

@@ -0,0 +1,127 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+package asm
+
+import (
+	"bytes"
+	"debug/macho"
+	"encoding/binary"
+	"testing"
+)
+
+// TestMachOObject checks the structure of the emitted MH_OBJECT: the two
+// sections and their addresses, the symbol table (types, sections, values)
+// and the __text relocation entries, parsed back with debug/macho.  No
+// Darwin toolchain is available on the test hosts, so the check is
+// structural — the ELF output carries the end-to-end link-and-run proof of
+// the shared symbol and relocation model.
+func TestMachOObject(t *testing.T) {
+	img := elfTestImage(t)
+	obj, err := img.MachOObject()
+	if err != nil {
+		t.Fatalf("MachOObject: %v", err)
+	}
+	f, err := macho.NewFile(bytes.NewReader(obj))
+	if err != nil {
+		t.Fatalf("parse emitted object: %v", err)
+	}
+	defer f.Close()
+
+	if f.Type != macho.TypeObj {
+		t.Errorf("file type = %v, want MH_OBJECT", f.Type)
+	}
+	if f.Cpu != macho.CpuAmd64 {
+		t.Errorf("cpu = %v, want CpuAmd64", f.Cpu)
+	}
+
+	text := f.Section("__text")
+	data := f.Section("__data")
+	if text == nil || data == nil {
+		t.Fatal("missing __text or __data section")
+	}
+	if text.Addr != 0 || text.Size != uint64(len(img.Code)) {
+		t.Errorf("__text addr/size = %#x/%d, want 0/%d", text.Addr, text.Size, len(img.Code))
+	}
+	if data.Addr != uint64(len(img.Code)) {
+		t.Errorf("__data addr = %#x, want %#x", data.Addr, len(img.Code))
+	}
+
+	// Symbol table: locals, exported definitions, undefined externals.
+	syms := f.Symtab.Syms
+	byName := map[string]macho.Symbol{}
+	for _, s := range syms {
+		byName[s.Name] = s
+	}
+	wantSym := func(name string, typ, sect uint8, value uint64) {
+		t.Helper()
+		s, ok := byName[name]
+		if !ok {
+			t.Errorf("symbol %q not found", name)
+			return
+		}
+		if s.Type != typ || s.Sect != sect || s.Value != value {
+			t.Errorf("%s: type/sect/value = %#x/%d/%#x, want %#x/%d/%#x",
+				name, s.Type, s.Sect, s.Value, typ, sect, value)
+		}
+	}
+	const (
+		defined   = nSect | nExt
+		local     = nSect
+		undefined = nUndf | nExt
+	)
+	wantSym("addq", defined, 1, 0)
+	wantSym("getanswer", defined, 1, 5)
+	wantSym("useextern", defined, 1, 13)
+	answer := byName["answer"]
+	if answer.Type != local || answer.Sect != 2 {
+		t.Errorf("answer: type/sect = %#x/%d, want %#x/2", answer.Type, answer.Sect, local)
+	}
+	wantSym("extvar", undefined, 0, 0)
+
+	// Relocations: both X86_64_RELOC_SIGNED, PC-relative, 4 bytes wide.
+	// The local one carries its section number in Value, the external one
+	// its symbol number.
+	if len(text.Relocs) != 2 {
+		t.Fatalf("__text relocs = %d, want 2", len(text.Relocs))
+	}
+	var sawLocal, sawExternal bool
+	for _, r := range text.Relocs {
+		if !r.Pcrel || r.Len != 2 || r.Type != x8664RelocSigned {
+			t.Errorf("reloc at %#x: pcrel/len/type = %v/%d/%d", r.Addr, r.Pcrel, r.Len, r.Type)
+		}
+		switch {
+		case r.Extern:
+			if name := syms[r.Value].Name; name != "extvar" {
+				t.Errorf("external reloc at %#x names %q, want extvar", r.Addr, name)
+			}
+			sawExternal = true
+		default:
+			if r.Value != 2 { // __data, the second section
+				t.Errorf("local reloc at %#x: section %d, want 2 (__data)", r.Addr, r.Value)
+			}
+			sawLocal = true
+		}
+	}
+	if !sawLocal || !sawExternal {
+		t.Errorf("relocs seen: local=%v external=%v, want both", sawLocal, sawExternal)
+	}
+
+	// The __text bytes are the image code, with the external displacement
+	// primed to addend − 4 and the local one left resolved.
+	textData, err := text.Data()
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := append([]byte(nil), img.Code...)
+	for _, fn := range img.Funcs {
+		for _, r := range fn.Relocs {
+			if r.Name == "extvar" {
+				binary.LittleEndian.PutUint32(want[fn.Offset+r.Off:], 0xfffffffc) // −4
+			}
+		}
+	}
+	if !bytes.Equal(textData, want) {
+		t.Errorf("__text bytes %x, want %x", textData, want)
+	}
+}

asm/vex.go

@@ -43,6 +43,13 @@ const (
 	// in ModRM.reg and the destination in r/m — the layout of the EVEX
 	// narrowing stores (VPMOVDW, VPMOVQD).
 	vexRMRev
+	// vexRMSrcLen is the two-operand conversion form `OP src, dst` whose
+	// vector length follows the source: the packed-double → dword
+	// conversions (VCVTPD2DQ/VCVTTPD2DQ and their X/Y spellings) narrow into
+	// an XMM destination, so the L bit rides with the wider source.  The
+	// mnemonic's spelling fixes the length (X = 128, Y = 256), which also
+	// covers a memory source.  ModRM.reg = dst, ModRM.rm = src, no vvvv.
+	vexRMSrcLen
 	// vexZero is the no-operand form (VZEROUPPER).
 	vexZero
 )
@@ -86,12 +93,29 @@ var vexTable = map[string]vexSpec{
 	// VEX.128/256.66.0F.WIG — packed double-precision arithmetic / logic.
 	"VADDPD":    {1, 0x58, 0, 1, -1, vexNDS3},
 	"VMULPD":    {1, 0x59, 0, 1, -1, vexNDS3},
+	"VSUBPD":    {1, 0x5C, 0, 1, -1, vexNDS3},
+	"VDIVPD":    {1, 0x5E, 0, 1, -1, vexNDS3},
+	"VMINPD":    {1, 0x5D, 0, 1, -1, vexNDS3},
+	"VMAXPD":    {1, 0x5F, 0, 1, -1, vexNDS3},
 	"VXORPD":    {1, 0x57, 0, 1, -1, vexNDS3},
 	"VUNPCKHPD": {1, 0x15, 0, 1, -1, vexNDS3},
+	"VUNPCKLPD": {1, 0x14, 0, 1, -1, vexNDS3},
 	// VEX.128.F2.0F.WIG — scalar double-precision arithmetic (the packed
 	// opcodes with an F2 pp).
 	"VADDSD": {1, 0x58, 0, 3, -1, vexNDS3},
+	"VSUBSD": {1, 0x5C, 0, 3, -1, vexNDS3},
 	"VMULSD": {1, 0x59, 0, 3, -1, vexNDS3},
+	"VDIVSD": {1, 0x5E, 0, 3, -1, vexNDS3},
+	"VMINSD": {1, 0x5D, 0, 3, -1, vexNDS3},
+	"VMAXSD": {1, 0x5F, 0, 3, -1, vexNDS3},
+	// VEX.128.F3.0F.WIG — scalar single-precision arithmetic (the packed
+	// opcodes with an F3 pp).
+	"VADDSS": {1, 0x58, 0, 2, -1, vexNDS3},
+	"VSUBSS": {1, 0x5C, 0, 2, -1, vexNDS3},
+	"VMULSS": {1, 0x59, 0, 2, -1, vexNDS3},
+	"VDIVSS": {1, 0x5E, 0, 2, -1, vexNDS3},
+	"VMINSS": {1, 0x5D, 0, 2, -1, vexNDS3},
+	"VMAXSS": {1, 0x5F, 0, 2, -1, vexNDS3},
 	// VEX.128/256.66.0F38.W1 — fused multiply-add (NDS form).
 	"VFMADD231PD": {2, 0xB8, 1, 1, -1, vexNDS3},
 
@@ -105,6 +129,19 @@ var vexTable = map[string]vexSpec{
 	// VEX.128/256.F3.0F.WIG — signed dword to packed double conversion
 	// (reg=dst, rm=src, no vvvv; the length follows the destination).
 	"VCVTDQ2PD": {1, 0xE6, 0, 2, -1, vexRM},
+	// VEX.128/256.0F.WIG — signed dword to packed single conversion
+	// (reg=dst, rm=src, no vvvv, no mandatory prefix).
+	"VCVTDQ2PS": {1, 0x5B, 0, 0, -1, vexRM},
+	// VEX.128/256.0F.WIG — packed single to packed double conversion
+	// (reg=dst, rm=src; the destination is the wide operand and sets the
+	// length).  Intel's maps prescribe the F3 prefix here (VEX.pp = 10), but
+	// the Go assembler emits the instruction with pp = 00, and gasm follows
+	// the Go assembler's bytes — its machine code is the oracle, not the
+	// manual.
+	"VCVTPS2PD": {1, 0x5A, 0, 0, -1, vexRM},
+	// VEX.128.F2.0F.WIG — duplicate the low double of each 128-bit lane
+	// (reg=dst, rm=src, no vvvv; the length follows the destination).
+	"VMOVDDUP": {1, 0x12, 0, 3, -1, vexRM},
 	// VEX.128/256.66.0F.WIG — move mask to a GPR (reg=gpr dst, rm=vec src).
 	"VPMOVMSKB": {1, 0xD7, 0, 1, -1, vexRM},
 	"VMOVMSKPS": {1, 0x50, 0, 0, -1, vexRM}, // no 66 prefix (that would be VMOVMSKPD)
@@ -138,6 +175,25 @@ var vexTable = map[string]vexSpec{
 
 	// VEX.128.0F.W0 — mask-register test (KTESTW k1, k2: reg = dst, rm = src).
 	"KTESTW": {1, 0x99, 0, 0, -1, vexRM},
+
+	// VEX.F2.0F — packed double to packed dword conversions, truncating and
+	// non-truncating.  The destination is always XMM; the X/Y spellings fix
+	// the source length (XMM/YMM), and VEX.L follows it — see vexSrcLen.
+	"VCVTPD2DQX":  {1, 0xE6, 0, 3, -1, vexRMSrcLen},
+	"VCVTPD2DQY":  {1, 0xE6, 0, 3, -1, vexRMSrcLen},
+	"VCVTTPD2DQX": {1, 0xE6, 0, 1, -1, vexRMSrcLen},
+	"VCVTTPD2DQY": {1, 0xE6, 0, 1, -1, vexRMSrcLen},
+}
+
+// vexSrcLen maps a source-length conversion mnemonic (the X/Y spellings of
+// the packed-double → dword conversions) to its fixed vector length:
+// X = 128 (L = 0), Y = 256 (L = 1).  The spelling fixes the length even for
+// a memory source, matching the Go assembler's ytab.
+var vexSrcLen = map[string]int{
+	"VCVTPD2DQX":  0,
+	"VCVTPD2DQY":  1,
+	"VCVTTPD2DQX": 0,
+	"VCVTTPD2DQY": 1,
 }
 
 // vexVarShift maps the shift mnemonics to their variable-count opcode — the
@@ -230,6 +286,8 @@ func (e *enc) encodeVex(mnemUpper string, ops []Operand) error {
 		return e.encodeVexNDS3Imm(spec, ops)
 	case vexExtract:
 		return e.encodeVexExtract(spec, ops)
+	case vexRMSrcLen:
+		return e.encodeVexRMSrcLen(mnemUpper, spec, ops)
 	case vexZero:
 		return e.encodeVexZero(mnemUpper, spec, ops)
 	}
@@ -295,6 +353,32 @@ func (e *enc) encodeVexRM(spec vexSpec, ops []Operand) error {
 	return e.emitVexFields(spec, l, regField, rBit, 15, src)
 }
 
+// encodeVexRMSrcLen encodes a length-narrowing conversion: OP src, dst with
+// the destination always XMM and the VEX.L bit following the source — fixed
+// by the mnemonic's spelling (VCVTPD2DQX = 128, VCVTPD2DQY = 256) even when
+// the source is memory.
+func (e *enc) encodeVexRMSrcLen(mnem string, spec vexSpec, ops []Operand) error {
+	if len(ops) != 2 {
+		return fmt.Errorf("conversion expects 2 operands, got %d", len(ops))
+	}
+	src, dst := ops[0], ops[1]
+	dstReg, ok := dst.(Reg)
+	if !ok || !dstReg.isVec() {
+		return fmt.Errorf("VEX destination must be a vector register")
+	}
+	ll, ok := vexSrcLen[mnem]
+	if !ok {
+		return fmt.Errorf("no fixed vector length for %s", mnem)
+	}
+	regField := dstReg.idx & 7
+	rBit := 0
+	if dstReg.idx >= 8 {
+		rBit = 1
+	}
+	// An unused vvvv field must be stored as all ones (v̄vvv = 1111).
+	return e.emitVexFields(spec, ll, regField, rBit, 15, src)
+}
+
 // encodeVexShiftImm encodes an immediate-shift instruction: OP $imm, src, dst.
 // The destination is carried in VEX.vvvv, the source in ModRM.rm, and the
 // shift kind in the ModRM.reg /digit.

asm/vex_test.go

@@ -160,78 +160,117 @@ func TestVexGroundTruth(t *testing.T) {
 		mnem   string
 		ops    []Operand
 		want   string
+		wantOp string // decoded mnemonic, when it differs from mnem (the X/Y spellings)
 	}{
 		// Three-operand NDS form.
-		{"VPADDQ Y8,Y9,Y8", "VPADDQ", []Operand{vreg(t, "Y8"), vreg(t, "Y9"), vreg(t, "Y8")}, "c44135d4c0"},
-		{"VPADDQ X9,X8,X8", "VPADDQ", []Operand{vreg(t, "X9"), vreg(t, "X8"), vreg(t, "X8")}, "c44139d4c1"},
-		{"VPXOR X7,X7,X7", "VPXOR", []Operand{vreg(t, "X7"), vreg(t, "X7"), vreg(t, "X7")}, "c5c1efff"},
-		{"VPSHUFB Y1,Y2,Y3", "VPSHUFB", []Operand{vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c4e26d00d9"},
-		{"VPMULLD Y1,Y2,Y3", "VPMULLD", []Operand{vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c4e26d40d9"},
-		{"VPUNPCKLDQ Y4,Y3,Y5", "VPUNPCKLDQ", []Operand{vreg(t, "Y4"), vreg(t, "Y3"), vreg(t, "Y5")}, "c5e562ec"},
-		{"VPERMD Y1,Y2,Y3", "VPERMD", []Operand{vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c4e26d36d9"},
+		{"VPADDQ Y8,Y9,Y8", "VPADDQ", []Operand{vreg(t, "Y8"), vreg(t, "Y9"), vreg(t, "Y8")}, "c44135d4c0", ""},
+		{"VPADDQ X9,X8,X8", "VPADDQ", []Operand{vreg(t, "X9"), vreg(t, "X8"), vreg(t, "X8")}, "c44139d4c1", ""},
+		{"VPXOR X7,X7,X7", "VPXOR", []Operand{vreg(t, "X7"), vreg(t, "X7"), vreg(t, "X7")}, "c5c1efff", ""},
+		{"VPSHUFB Y1,Y2,Y3", "VPSHUFB", []Operand{vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c4e26d00d9", ""},
+		{"VPMULLD Y1,Y2,Y3", "VPMULLD", []Operand{vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c4e26d40d9", ""},
+		{"VPUNPCKLDQ Y4,Y3,Y5", "VPUNPCKLDQ", []Operand{vreg(t, "Y4"), vreg(t, "Y3"), vreg(t, "Y5")}, "c5e562ec", ""},
+		{"VPERMD Y1,Y2,Y3", "VPERMD", []Operand{vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c4e26d36d9", ""},
 		// Floating point (packed and scalar) and FMA — same NDS form, the pp
 		// bits and map select the operation.
-		{"VADDPD Y9,Y8,Y8", "VADDPD", []Operand{vreg(t, "Y9"), vreg(t, "Y8"), vreg(t, "Y8")}, "c4413d58c1"},
-		{"VADDPD X1,X2,X3", "VADDPD", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5e958d9"},
-		{"VMULPD Y12,Y12,Y12", "VMULPD", []Operand{vreg(t, "Y12"), vreg(t, "Y12"), vreg(t, "Y12")}, "c4411d59e4"},
-		{"VXORPD Y8,Y8,Y8", "VXORPD", []Operand{vreg(t, "Y8"), vreg(t, "Y8"), vreg(t, "Y8")}, "c4413d57c0"},
-		{"VUNPCKHPD X8,X8,X9", "VUNPCKHPD", []Operand{vreg(t, "X8"), vreg(t, "X8"), vreg(t, "X9")}, "c4413915c8"},
-		{"VADDSD X9,X8,X8", "VADDSD", []Operand{vreg(t, "X9"), vreg(t, "X8"), vreg(t, "X8")}, "c4413b58c1"},
-		{"VMULSD X0,X1,X1", "VMULSD", []Operand{vreg(t, "X0"), vreg(t, "X1"), vreg(t, "X1")}, "c5f359c8"},
-		{"VFMADD231PD Y14,Y12,Y8", "VFMADD231PD", []Operand{vreg(t, "Y14"), vreg(t, "Y12"), vreg(t, "Y8")}, "c4429db8c6"},
-		{"VFMADD231PD (DI),Y12,Y8", "VFMADD231PD", []Operand{Ptr(DI, 0, 32), vreg(t, "Y12"), vreg(t, "Y8")}, "c4629db807"},
+		{"VADDPD Y9,Y8,Y8", "VADDPD", []Operand{vreg(t, "Y9"), vreg(t, "Y8"), vreg(t, "Y8")}, "c4413d58c1", ""},
+		{"VADDPD X1,X2,X3", "VADDPD", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5e958d9", ""},
+		{"VMULPD Y12,Y12,Y12", "VMULPD", []Operand{vreg(t, "Y12"), vreg(t, "Y12"), vreg(t, "Y12")}, "c4411d59e4", ""},
+		{"VXORPD Y8,Y8,Y8", "VXORPD", []Operand{vreg(t, "Y8"), vreg(t, "Y8"), vreg(t, "Y8")}, "c4413d57c0", ""},
+		{"VUNPCKHPD X8,X8,X9", "VUNPCKHPD", []Operand{vreg(t, "X8"), vreg(t, "X8"), vreg(t, "X9")}, "c4413915c8", ""},
+		{"VADDSD X9,X8,X8", "VADDSD", []Operand{vreg(t, "X9"), vreg(t, "X8"), vreg(t, "X8")}, "c4413b58c1", ""},
+		{"VMULSD X0,X1,X1", "VMULSD", []Operand{vreg(t, "X0"), vreg(t, "X1"), vreg(t, "X1")}, "c5f359c8", ""},
+		{"VFMADD231PD Y14,Y12,Y8", "VFMADD231PD", []Operand{vreg(t, "Y14"), vreg(t, "Y12"), vreg(t, "Y8")}, "c4429db8c6", ""},
+		{"VFMADD231PD (DI),Y12,Y8", "VFMADD231PD", []Operand{Ptr(DI, 0, 32), vreg(t, "Y12"), vreg(t, "Y8")}, "c4629db807", ""},
 		// Two-operand reg/rm form (v̄vvv must be 1111).
-		{"VPMOVSXDQ X0,Y4", "VPMOVSXDQ", []Operand{vreg(t, "X0"), vreg(t, "Y4")}, "c4e27d25e0"},
-		{"VPMOVSXWD (SI),Y0", "VPMOVSXWD", []Operand{Ptr(SI, 0, 8), vreg(t, "Y0")}, "c4e27d2306"},
-		{"VPBROADCASTD X0,Y15", "VPBROADCASTD", []Operand{vreg(t, "X0"), vreg(t, "Y15")}, "c4627d58f8"},
-		{"VCVTDQ2PD X12,Y12", "VCVTDQ2PD", []Operand{vreg(t, "X12"), vreg(t, "Y12")}, "c4417ee6e4"},
-		{"VCVTDQ2PD (SI),Y4", "VCVTDQ2PD", []Operand{Ptr(SI, 0, 16), vreg(t, "Y4")}, "c5fee626"},
-		{"VPMOVMSKB X11,AX", "VPMOVMSKB", []Operand{vreg(t, "X11"), AX}, "c4c179d7c3"},
-		{"VMOVMSKPS Y7,AX", "VMOVMSKPS", []Operand{vreg(t, "Y7"), AX}, "c5fc50c7"},
+		{"VPMOVSXDQ X0,Y4", "VPMOVSXDQ", []Operand{vreg(t, "X0"), vreg(t, "Y4")}, "c4e27d25e0", ""},
+		{"VPMOVSXWD (SI),Y0", "VPMOVSXWD", []Operand{Ptr(SI, 0, 8), vreg(t, "Y0")}, "c4e27d2306", ""},
+		{"VPBROADCASTD X0,Y15", "VPBROADCASTD", []Operand{vreg(t, "X0"), vreg(t, "Y15")}, "c4627d58f8", ""},
+		{"VCVTDQ2PD X12,Y12", "VCVTDQ2PD", []Operand{vreg(t, "X12"), vreg(t, "Y12")}, "c4417ee6e4", ""},
+		{"VCVTDQ2PD (SI),Y4", "VCVTDQ2PD", []Operand{Ptr(SI, 0, 16), vreg(t, "Y4")}, "c5fee626", ""},
+		{"VPMOVMSKB X11,AX", "VPMOVMSKB", []Operand{vreg(t, "X11"), AX}, "c4c179d7c3", ""},
+		{"VMOVMSKPS Y7,AX", "VMOVMSKPS", []Operand{vreg(t, "Y7"), AX}, "c5fc50c7", ""},
 		// Immediate shifts.
-		{"VPSLLD $1,Y3,Y4", "VPSLLD", []Operand{Imm(1), vreg(t, "Y3"), vreg(t, "Y4")}, "c5dd72f301"},
-		{"VPSRLQ $2,Y5,Y6", "VPSRLQ", []Operand{Imm(2), vreg(t, "Y5"), vreg(t, "Y6")}, "c5cd73d502"},
+		{"VPSLLD $1,Y3,Y4", "VPSLLD", []Operand{Imm(1), vreg(t, "Y3"), vreg(t, "Y4")}, "c5dd72f301", ""},
+		{"VPSRLQ $2,Y5,Y6", "VPSRLQ", []Operand{Imm(2), vreg(t, "Y5"), vreg(t, "Y6")}, "c5cd73d502", ""},
 		// Variable-count shifts: the count lives in an XMM register or memory
 		// and the instruction takes the NDS form.
-		{"VPSRLQ X0,Y8,Y8", "VPSRLQ", []Operand{vreg(t, "X0"), vreg(t, "Y8"), vreg(t, "Y8")}, "c53dd3c0"},
-		{"VPSRLQ (AX),Y8,Y8", "VPSRLQ", []Operand{Ptr(AX, 0, 16), vreg(t, "Y8"), vreg(t, "Y8")}, "c53dd300"},
-		{"VPSLLD X0,Y1,Y2", "VPSLLD", []Operand{vreg(t, "X0"), vreg(t, "Y1"), vreg(t, "Y2")}, "c5f5f2d0"},
-		{"VPSRLD X0,Y1,Y2", "VPSRLD", []Operand{vreg(t, "X0"), vreg(t, "Y1"), vreg(t, "Y2")}, "c5f5d2d0"},
-		{"VPSRAD X0,Y1,Y2", "VPSRAD", []Operand{vreg(t, "X0"), vreg(t, "Y1"), vreg(t, "Y2")}, "c5f5e2d0"},
-		{"VPSLLQ X0,Y1,Y2", "VPSLLQ", []Operand{vreg(t, "X0"), vreg(t, "Y1"), vreg(t, "Y2")}, "c5f5f3d0"},
+		{"VPSRLQ X0,Y8,Y8", "VPSRLQ", []Operand{vreg(t, "X0"), vreg(t, "Y8"), vreg(t, "Y8")}, "c53dd3c0", ""},
+		{"VPSRLQ (AX),Y8,Y8", "VPSRLQ", []Operand{Ptr(AX, 0, 16), vreg(t, "Y8"), vreg(t, "Y8")}, "c53dd300", ""},
+		{"VPSLLD X0,Y1,Y2", "VPSLLD", []Operand{vreg(t, "X0"), vreg(t, "Y1"), vreg(t, "Y2")}, "c5f5f2d0", ""},
+		{"VPSRLD X0,Y1,Y2", "VPSRLD", []Operand{vreg(t, "X0"), vreg(t, "Y1"), vreg(t, "Y2")}, "c5f5d2d0", ""},
+		{"VPSRAD X0,Y1,Y2", "VPSRAD", []Operand{vreg(t, "X0"), vreg(t, "Y1"), vreg(t, "Y2")}, "c5f5e2d0", ""},
+		{"VPSLLQ X0,Y1,Y2", "VPSLLQ", []Operand{vreg(t, "X0"), vreg(t, "Y1"), vreg(t, "Y2")}, "c5f5f3d0", ""},
 		// Immediate shuffle (reg=dst, rm=src, imm8).
-		{"VPSHUFD $0xEE,X8,X9", "VPSHUFD", []Operand{Imm(0xEE), vreg(t, "X8"), vreg(t, "X9")}, "c4417970c8ee"},
-		{"VPSHUFD $0xEE,Y1,Y2", "VPSHUFD", []Operand{Imm(0xEE), vreg(t, "Y1"), vreg(t, "Y2")}, "c5fd70d1ee"},
-		{"VPERMQ $0x1B,Y1,Y2", "VPERMQ", []Operand{Imm(0x1B), vreg(t, "Y1"), vreg(t, "Y2")}, "c4e3fd00d11b"},
-		{"VPERMQ $0x1B,Y11,Y12", "VPERMQ", []Operand{Imm(0x1B), vreg(t, "Y11"), vreg(t, "Y12")}, "c443fd00e31b"},
+		{"VPSHUFD $0xEE,X8,X9", "VPSHUFD", []Operand{Imm(0xEE), vreg(t, "X8"), vreg(t, "X9")}, "c4417970c8ee", ""},
+		{"VPSHUFD $0xEE,Y1,Y2", "VPSHUFD", []Operand{Imm(0xEE), vreg(t, "Y1"), vreg(t, "Y2")}, "c5fd70d1ee", ""},
+		{"VPERMQ $0x1B,Y1,Y2", "VPERMQ", []Operand{Imm(0x1B), vreg(t, "Y1"), vreg(t, "Y2")}, "c4e3fd00d11b", ""},
+		{"VPERMQ $0x1B,Y11,Y12", "VPERMQ", []Operand{Imm(0x1B), vreg(t, "Y11"), vreg(t, "Y12")}, "c443fd00e31b", ""},
 		// Three-operand + immediate (reg=dst, vvvv=src1, rm=src2, imm8).
-		{"VSHUFPD $1,X1,X2,X3", "VSHUFPD", []Operand{Imm(1), vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5e9c6d901"},
-		{"VSHUFPD $1,Y1,Y2,Y3", "VSHUFPD", []Operand{Imm(1), vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c5edc6d901"},
-		{"VPERM2I128 $0x31,Y1,Y2,Y3", "VPERM2I128", []Operand{Imm(0x31), vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c4e36d46d931"},
-		{"VINSERTI128 $1,X5,Y1,Y2", "VINSERTI128", []Operand{Imm(1), vreg(t, "X5"), vreg(t, "Y1"), vreg(t, "Y2")}, "c4e37538d501"},
+		{"VSHUFPD $1,X1,X2,X3", "VSHUFPD", []Operand{Imm(1), vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5e9c6d901", ""},
+		{"VSHUFPD $1,Y1,Y2,Y3", "VSHUFPD", []Operand{Imm(1), vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c5edc6d901", ""},
+		{"VPERM2I128 $0x31,Y1,Y2,Y3", "VPERM2I128", []Operand{Imm(0x31), vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c4e36d46d931", ""},
+		{"VINSERTI128 $1,X5,Y1,Y2", "VINSERTI128", []Operand{Imm(1), vreg(t, "X5"), vreg(t, "Y1"), vreg(t, "Y2")}, "c4e37538d501", ""},
 		// Lane extract (reg=YMM source, rm=XMM/memory destination, imm8).
-		{"VEXTRACTI128 $1,Y8,X9", "VEXTRACTI128", []Operand{Imm(1), vreg(t, "Y8"), vreg(t, "X9")}, "c4437d39c101"},
-		{"VEXTRACTI128 $1,Y8,(DI)", "VEXTRACTI128", []Operand{Imm(1), vreg(t, "Y8"), Ptr(DI, 0, 16)}, "c4637d390701"},
-		{"VEXTRACTF128 $1,Y8,X9", "VEXTRACTF128", []Operand{Imm(1), vreg(t, "Y8"), vreg(t, "X9")}, "c4437d19c101"},
+		{"VEXTRACTI128 $1,Y8,X9", "VEXTRACTI128", []Operand{Imm(1), vreg(t, "Y8"), vreg(t, "X9")}, "c4437d39c101", ""},
+		{"VEXTRACTI128 $1,Y8,(DI)", "VEXTRACTI128", []Operand{Imm(1), vreg(t, "Y8"), Ptr(DI, 0, 16)}, "c4637d390701", ""},
+		{"VEXTRACTF128 $1,Y8,X9", "VEXTRACTF128", []Operand{Imm(1), vreg(t, "Y8"), vreg(t, "X9")}, "c4437d19c101", ""},
 		// Moves — each direction picks its own opcode and VEX.W.
-		{"VMOVDQU (SI),Y1", "VMOVDQU", []Operand{Ptr(SI, 0, 32), vreg(t, "Y1")}, "c5fe6f0e"},
-		{"VMOVDQU Y3,(DI)", "VMOVDQU", []Operand{vreg(t, "Y3"), Ptr(DI, 0, 32)}, "c5fe7f1f"},
-		{"VMOVDQU X1,X2", "VMOVDQU", []Operand{vreg(t, "X1"), vreg(t, "X2")}, "c5fa7fca"},
-		{"VMOVUPD (DI),Y14", "VMOVUPD", []Operand{Ptr(DI, 0, 32), vreg(t, "Y14")}, "c57d1037"},
-		{"VMOVUPD Y14,(DI)", "VMOVUPD", []Operand{vreg(t, "Y14"), Ptr(DI, 0, 32)}, "c57d1137"},
-		{"VMOVUPD X1,X2", "VMOVUPD", []Operand{vreg(t, "X1"), vreg(t, "X2")}, "c5f911ca"},
-		{"VMOVQ X8,AX", "VMOVQ", []Operand{vreg(t, "X8"), AX}, "c461f97ec0"},
-		{"VMOVQ AX,X9", "VMOVQ", []Operand{AX, vreg(t, "X9")}, "c461f96ec8"},
-		{"VMOVQ X8,(DI)", "VMOVQ", []Operand{vreg(t, "X8"), Ptr(DI, 0, 8)}, "c461f97e07"},
-		{"VMOVQ (SI),X9", "VMOVQ", []Operand{Ptr(SI, 0, 8), vreg(t, "X9")}, "c461f96e0e"},
-		{"VMOVQ X8,X2", "VMOVQ", []Operand{vreg(t, "X8"), vreg(t, "X2")}, "c579d6c2"},
-		{"VMOVQ X2,X8", "VMOVQ", []Operand{vreg(t, "X2"), vreg(t, "X8")}, "c4c179d6d0"},
-		{"VMOVD X0,(SI)", "VMOVD", []Operand{vreg(t, "X0"), Ptr(SI, 0, 4)}, "c5f97e06"},
-		{"VMOVD AX,X0", "VMOVD", []Operand{AX, vreg(t, "X0")}, "c5f96ec0"},
-		{"VMOVSD (SI),X8", "VMOVSD", []Operand{Ptr(SI, 0, 8), vreg(t, "X8")}, "c57b1006"},
-		{"VMOVSD X8,(SI)", "VMOVSD", []Operand{vreg(t, "X8"), Ptr(SI, 0, 8)}, "c57b1106"},
+		{"VMOVDQU (SI),Y1", "VMOVDQU", []Operand{Ptr(SI, 0, 32), vreg(t, "Y1")}, "c5fe6f0e", ""},
+		{"VMOVDQU Y3,(DI)", "VMOVDQU", []Operand{vreg(t, "Y3"), Ptr(DI, 0, 32)}, "c5fe7f1f", ""},
+		{"VMOVDQU X1,X2", "VMOVDQU", []Operand{vreg(t, "X1"), vreg(t, "X2")}, "c5fa7fca", ""},
+		{"VMOVUPD (DI),Y14", "VMOVUPD", []Operand{Ptr(DI, 0, 32), vreg(t, "Y14")}, "c57d1037", ""},
+		{"VMOVUPD Y14,(DI)", "VMOVUPD", []Operand{vreg(t, "Y14"), Ptr(DI, 0, 32)}, "c57d1137", ""},
+		{"VMOVUPD X1,X2", "VMOVUPD", []Operand{vreg(t, "X1"), vreg(t, "X2")}, "c5f911ca", ""},
+		{"VMOVQ X8,AX", "VMOVQ", []Operand{vreg(t, "X8"), AX}, "c461f97ec0", ""},
+		{"VMOVQ AX,X9", "VMOVQ", []Operand{AX, vreg(t, "X9")}, "c461f96ec8", ""},
+		{"VMOVQ X8,(DI)", "VMOVQ", []Operand{vreg(t, "X8"), Ptr(DI, 0, 8)}, "c461f97e07", ""},
+		{"VMOVQ (SI),X9", "VMOVQ", []Operand{Ptr(SI, 0, 8), vreg(t, "X9")}, "c461f96e0e", ""},
+		{"VMOVQ X8,X2", "VMOVQ", []Operand{vreg(t, "X8"), vreg(t, "X2")}, "c579d6c2", ""},
+		{"VMOVQ X2,X8", "VMOVQ", []Operand{vreg(t, "X2"), vreg(t, "X8")}, "c4c179d6d0", ""},
+		{"VMOVD X0,(SI)", "VMOVD", []Operand{vreg(t, "X0"), Ptr(SI, 0, 4)}, "c5f97e06", ""},
+		{"VMOVD AX,X0", "VMOVD", []Operand{AX, vreg(t, "X0")}, "c5f96ec0", ""},
+		{"VMOVSD (SI),X8", "VMOVSD", []Operand{Ptr(SI, 0, 8), vreg(t, "X8")}, "c57b1006", ""},
+		{"VMOVSD X8,(SI)", "VMOVSD", []Operand{vreg(t, "X8"), Ptr(SI, 0, 8)}, "c57b1106", ""},
+		// Packed double arithmetic and unpack — the NDS form, the opcode
+		// selects the operation.
+		{"VSUBPD Y1,Y2,Y3", "VSUBPD", []Operand{vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c5ed5cd9", ""},
+		{"VDIVPD X1,X2,X3", "VDIVPD", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5e95ed9", ""},
+		{"VMINPD Y1,Y2,Y3", "VMINPD", []Operand{vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c5ed5dd9", ""},
+		{"VMAXPD X4,X5,X6", "VMAXPD", []Operand{vreg(t, "X4"), vreg(t, "X5"), vreg(t, "X6")}, "c5d15ff4", ""},
+		{"VUNPCKLPD X1,X2,X3", "VUNPCKLPD", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5e914d9", ""},
+		{"VUNPCKLPD Y1,Y2,Y3", "VUNPCKLPD", []Operand{vreg(t, "Y1"), vreg(t, "Y2"), vreg(t, "Y3")}, "c5ed14d9", ""},
+		{"VSUBPD (AX),X1,X2", "VSUBPD", []Operand{Ptr(AX, 0, 16), vreg(t, "X1"), vreg(t, "X2")}, "c5f15c10", ""},
+		// Scalar double and single arithmetic (F2 / F3 pp, 128-bit only).
+		{"VSUBSD X1,X2,X3", "VSUBSD", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5eb5cd9", ""},
+		{"VDIVSD X7,X1,X2", "VDIVSD", []Operand{vreg(t, "X7"), vreg(t, "X1"), vreg(t, "X2")}, "c5f35ed7", ""},
+		{"VMINSD X1,X2,X3", "VMINSD", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5eb5dd9", ""},
+		{"VMAXSD X3,X4,X5", "VMAXSD", []Operand{vreg(t, "X3"), vreg(t, "X4"), vreg(t, "X5")}, "c5db5feb", ""},
+		{"VADDSS X1,X2,X3", "VADDSS", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5ea58d9", ""},
+		{"VSUBSS X1,X2,X3", "VSUBSS", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5ea5cd9", ""},
+		{"VMULSS X9,X10,X11", "VMULSS", []Operand{vreg(t, "X9"), vreg(t, "X10"), vreg(t, "X11")}, "c4412a59d9", ""},
+		{"VDIVSS X1,X2,X3", "VDIVSS", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5ea5ed9", ""},
+		{"VMINSS X6,X7,X8", "VMINSS", []Operand{vreg(t, "X6"), vreg(t, "X7"), vreg(t, "X8")}, "c5425dc6", ""},
+		{"VMAXSS X1,X2,X3", "VMAXSS", []Operand{vreg(t, "X1"), vreg(t, "X2"), vreg(t, "X3")}, "c5ea5fd9", ""},
+		{"VADDSD 8(AX),X1,X2", "VADDSD", []Operand{Ptr(AX, 8, 8), vreg(t, "X1"), vreg(t, "X2")}, "c5f3585008", ""},
+		// VMOVDDUP — duplicate the low double (reg=dst, rm=src, F2 pp).
+		{"VMOVDDUP X1,X2", "VMOVDDUP", []Operand{vreg(t, "X1"), vreg(t, "X2")}, "c5fb12d1", ""},
+		{"VMOVDDUP Y1,Y2", "VMOVDDUP", []Operand{vreg(t, "Y1"), vreg(t, "Y2")}, "c5ff12d1", ""},
+		{"VMOVDDUP 8(AX),X1", "VMOVDDUP", []Operand{Ptr(AX, 8, 8), vreg(t, "X1")}, "c5fb124808", ""},
+		// Conversions: DQ→PS (no prefix), PS→PD (Go emits it without the F3
+		// prefix — see the table comment), DQ→PD.
+		{"VCVTDQ2PS X1,X2", "VCVTDQ2PS", []Operand{vreg(t, "X1"), vreg(t, "X2")}, "c5f85bd1", ""},
+		{"VCVTDQ2PS Y3,Y4", "VCVTDQ2PS", []Operand{vreg(t, "Y3"), vreg(t, "Y4")}, "c5fc5be3", ""},
+		{"VCVTPS2PD X1,X2", "VCVTPS2PD", []Operand{vreg(t, "X1"), vreg(t, "X2")}, "c5f85ad1", ""},
+		{"VCVTPS2PD X1,Y2", "VCVTPS2PD", []Operand{vreg(t, "X1"), vreg(t, "Y2")}, "c5fc5ad1", ""},
+		// PD→DQ conversions: the X/Y spellings fix the source length and the
+		// destination is always XMM; the decoder reports the base mnemonic.
+		{"VCVTPD2DQX X1,X2", "VCVTPD2DQX", []Operand{vreg(t, "X1"), vreg(t, "X2")}, "c5fbe6d1", "VCVTPD2DQ"},
+		{"VCVTPD2DQY Y1,X2", "VCVTPD2DQY", []Operand{vreg(t, "Y1"), vreg(t, "X2")}, "c5ffe6d1", "VCVTPD2DQ"},
+		{"VCVTTPD2DQX X3,X4", "VCVTTPD2DQX", []Operand{vreg(t, "X3"), vreg(t, "X4")}, "c5f9e6e3", "VCVTTPD2DQ"},
+		{"VCVTTPD2DQY Y5,X6", "VCVTTPD2DQY", []Operand{vreg(t, "Y5"), vreg(t, "X6")}, "c5fde6f5", "VCVTTPD2DQ"},
+		{"VCVTPD2DQY (AX),X1", "VCVTPD2DQY", []Operand{Ptr(AX, 0, 32), vreg(t, "X1")}, "c5ffe608", "VCVTPD2DQ"},
 		// No-operand.
-		{"VZEROUPPER", "VZEROUPPER", nil, "c5f877"},
+		{"VZEROUPPER", "VZEROUPPER", nil, "c5f877", ""},
 	}
 	for _, c := range cases {
 		code, err := Encode(c.mnem, c.ops...)
@@ -251,7 +290,11 @@ func TestVexGroundTruth(t *testing.T) {
 		if inst.Len != len(code) {
 			t.Errorf("%s: Decode consumed %d of %d bytes", c.name, inst.Len, len(code))
 		}
-		if inst.Op.String() != c.mnem {
+		wantOp := c.wantOp
+		if wantOp == "" {
+			wantOp = c.mnem
+		}
+		if inst.Op.String() != wantOp {
 			t.Errorf("%s: decoded as %s", c.name, inst.Op.String())
 		}
 	}

cmd/gasm/main.go

@@ -11,7 +11,9 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"io/fs"
 	"os"
+	"path/filepath"
 	"strings"
 
 	"sourcedock.dev/petrbalvin/gasm-devkit/arch"
@@ -26,7 +28,7 @@ import (
 
 // version is the release version, stamped at build time via
 // -ldflags "-X main.version=…" (defaulting to the current release).
-var version = "0.6.0"
+var version = "0.11.0"
 
 func main() {
 	if len(os.Args) < 2 {
@@ -47,30 +49,72 @@ func main() {
 	case "lsp":
 		os.Exit(cmdLSP(os.Args[2:]))
 	case "version", "--version", "-V":
-		fmt.Printf("gasm %s\n", version)
-	case "help", "-h", "--help":
+		os.Exit(cmdVersion())
+	case "help", "--help", "-h":
 		usage(os.Stdout)
 	default:
-		fmt.Fprintf(os.Stderr, "gasm: unknown command %q\n\n", os.Args[1])
-		usage(os.Stderr)
+		fmt.Fprintf(os.Stderr, "gasm: unknown command %q — run \"gasm --help\" for usage\n", os.Args[1])
 		os.Exit(2)
 	}
 }
 
+// cmdVersion prints the release version.
+func cmdVersion() int {
+	fmt.Printf("gasm %s\n", version)
+	return 0
+}
+
 func usage(w io.Writer) {
-	fmt.Fprintf(w, `gasm %s — developer tooling for Go's Plan 9 assembler
+	fmt.Fprintf(w, `gasm %s — developer tooling for Go's Plan 9 assembler (GAsm)
+
+gasm bundles a lexer, parser, formatter, linter, standalone assembler and
+language server for Plan 9 assembly into one self-contained binary.
 
 Usage:
-  gasm tokens <file>          print the lexical token stream
-  gasm parse  <file>          parse and report syntax errors
-  gasm fmt    [-w] <file...>  canonicalise formatting (-w writes in place)
-  gasm lint   <file...>       run static checks
-  gasm asm    [-o out.bin] <file>  assemble to machine code (amd64, Phase 2)
-  gasm lsp                    run the language server over stdio
-  gasm version                print the version
+  gasm <command> [arguments]
+  gasm [flags]
+
+Commands:
+  tokens    print the lexical token stream
+  parse     parse and report syntax errors
+  fmt       canonicalise formatting (gofmt for assembly)
+  lint      run static checks
+  asm       assemble .s files to machine code (amd64)
+  lsp       run the language server over stdio
+  version   print the version (same as --version)
+
+Flags:
+  -h, --help      show this help
+  -V, --version   print the version
+
+Run "gasm <command> -h" for a command's usage and flags.
+
+Examples:
+  gasm fmt                  reformat every .s below the current directory
+  gasm lint go-flac/*.s     run static checks over the kernels
+  gasm asm -o k.bin kern_amd64.s
+  gasm asm --format elf -o k.o kern_amd64.s
 `, version)
 }
 
+// newCommand returns the FlagSet of a subcommand whose -h/--help prints a
+// proper usage block: the one-line usage, the long description and the flag
+// defaults.  The flag package routes -h/--help to fs.Usage and exits 0.
+func newCommand(name, usageLine, long string) *flag.FlagSet {
+	fs := flag.NewFlagSet(name, flag.ExitOnError)
+	fs.Usage = func() {
+		w := fs.Output()
+		fmt.Fprintf(w, "Usage: %s\n\n%s\n", usageLine, strings.TrimSpace(long))
+		hasFlags := false
+		fs.VisitAll(func(*flag.Flag) { hasFlags = true })
+		if hasFlags {
+			fmt.Fprintln(w, "\nFlags:")
+			fs.PrintDefaults()
+		}
+	}
+	return fs
+}
+
 // readSource returns the contents of path, or stdin when path is "-".
 func readSource(path string) (string, error) {
 	if path == "-" {
@@ -82,7 +126,10 @@ func readSource(path string) (string, error) {
 }
 
 func cmdTokens(args []string) int {
-	fs := flag.NewFlagSet("tokens", flag.ExitOnError)
+	fs := newCommand("tokens", "gasm tokens <file>", `
+Print the lexical token stream of FILE: position, token kind and text, one
+token per line.  FILE may be "-" to read standard input.
+`)
 	fs.Parse(args)
 	if fs.NArg() != 1 {
 		fmt.Fprintln(os.Stderr, "usage: gasm tokens <file>")
@@ -100,7 +147,11 @@ func cmdTokens(args []string) int {
 }
 
 func cmdParse(args []string) int {
-	fs := flag.NewFlagSet("parse", flag.ExitOnError)
+	fs := newCommand("parse", "gasm parse <file>", `
+Parse FILE and report syntax errors on stderr.  On success, print how many
+declarations and TEXT functions the file contains.  FILE may be "-" to read
+standard input.
+`)
 	fs.Parse(args)
 	if fs.NArg() != 1 {
 		fmt.Fprintln(os.Stderr, "usage: gasm parse <file>")
@@ -130,15 +181,49 @@ func cmdParse(args []string) int {
 }
 
 func cmdFmt(args []string) int {
-	fs := flag.NewFlagSet("fmt", flag.ExitOnError)
+	fs := newCommand("fmt", "gasm fmt [-w] [path...]", `
+Canonicalise the formatting of Plan 9 assembly sources: indentation, operand
+spacing, per-function mnemonic alignment and blank-line layout (exactly one
+blank line before each label, TEXT and GLOBL block).  Formatting is
+idempotent and preserves every line, comments included.
+
+With no paths — or a directory path — every .s file below it is reformatted
+in place and the changed files are listed, the way go fmt does; "." and "_"
+directories are skipped.  Explicit file paths print to stdout unless -w is
+given.
+`)
 	write := fs.Bool("w", false, "write result to the source file")
 	fs.Parse(args)
-	if fs.NArg() == 0 {
-		fmt.Fprintln(os.Stderr, "usage: gasm fmt [-w] <file...>")
-		return 2
+	// Like go fmt: with no arguments, or with a directory argument, every .s
+	// file below the directory is formatted in place and the names of the
+	// changed files are listed; explicit file arguments keep the -w / stdout
+	// behaviour.
+	paths := fs.Args()
+	dirMode := len(paths) == 0
+	if dirMode {
+		paths = []string{"."}
+	}
+	var files []string
+	for _, p := range paths {
+		info, err := os.Stat(p)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, "gasm:", err)
+			return 1
+		}
+		if info.IsDir() {
+			dirMode = true
+			found, err := asmFiles(p)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, "gasm:", err)
+				return 1
+			}
+			files = append(files, found...)
+			continue
+		}
+		files = append(files, p)
 	}
 	rc := 0
-	for _, path := range fs.Args() {
+	for _, path := range files {
 		src, err := readSource(path)
 		if err != nil {
 			fmt.Fprintln(os.Stderr, "gasm:", err)
@@ -146,11 +231,15 @@ func cmdFmt(args []string) int {
 			continue
 		}
 		out := format.Source(path, src)
-		if *write {
+		if dirMode || *write {
 			if out != src {
 				if err := os.WriteFile(path, []byte(out), 0o644); err != nil {
 					fmt.Fprintln(os.Stderr, "gasm:", err)
 					rc = 1
+					continue
+				}
+				if dirMode {
+					fmt.Println(path)
 				}
 			}
 			continue
@@ -160,8 +249,40 @@ func cmdFmt(args []string) int {
 	return rc
 }
 
+// asmFiles collects the .s files below dir, skipping directories whose name
+// starts with "." or "_" — as the go tooling does, which keeps .git and
+// scratch or reference trees (e.g. _refs) untouched.
+func asmFiles(dir string) ([]string, error) {
+	var out []string
+	err := filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() {
+			if path != dir && (strings.HasPrefix(d.Name(), ".") || strings.HasPrefix(d.Name(), "_")) {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+		if strings.HasSuffix(d.Name(), ".s") {
+			out = append(out, path)
+		}
+		return nil
+	})
+	return out, err
+}
+
 func cmdLint(args []string) int {
-	fs := flag.NewFlagSet("lint", flag.ExitOnError)
+	fs := newCommand("lint", "gasm lint <file...>", `
+Run the static checks over the given files and print diagnostics as
+"file:line:col: severity: message [code]".  The exit status is non-zero when
+an error-severity diagnostic is found; warnings (e.g. the register-clobber
+audit) do not affect it.
+
+Rules include unknown-instruction, operand-count, undefined-label,
+duplicate-label, missing-ret, missing-textflag-include, abi-argsize,
+unreachable-code, register-clobber and funcdata-pcdata.
+`)
 	disable := fs.String("disable", "", "comma-separated rule codes to disable")
 	fs.Parse(args)
 	if fs.NArg() == 0 {
@@ -202,7 +323,13 @@ func cmdLint(args []string) int {
 }
 
 func cmdLSP(args []string) int {
-	fs := flag.NewFlagSet("lsp", flag.ExitOnError)
+	fs := newCommand("lsp", "gasm lsp", `
+Run the language server over standard input/output: JSON-RPC 2.0 with
+Content-Length framing.  Point an LSP-capable editor at the binary and
+associate it with .s files; the target architecture is inferred from the file
+suffix (_amd64.s, _arm64.s, _riscv64.s, _loong64.s).  Provides completion,
+hover, document symbols, diagnostics and semantic-token highlighting.
+`)
 	fs.Parse(args)
 	srv := lsp.New(os.Stdin, os.Stdout)
 	if err := srv.Run(); err != nil {
@@ -213,11 +340,24 @@ func cmdLSP(args []string) int {
 }
 
 func cmdAsm(args []string) int {
-	fs := flag.NewFlagSet("asm", flag.ExitOnError)
-	out := fs.String("o", "", "write the concatenated machine code to this file")
+	fs := newCommand("asm", "gasm asm [--format raw|elf|macho] [-o out] <file>", `
+Assemble FILE (amd64) without the Go toolchain: every TEXT function is
+encoded to machine code — scalar, VEX/AVX2 and EVEX/AVX-512 instructions,
+FP/SP frame mapping, local labels and file-local static symbols (GLOBL/DATA)
+resolved RIP-relative — and printed as a hex dump.
+
+With -o the output is written to a file instead.  The --format flag selects
+what is written: raw (the default) concatenates the functions and the data
+section into one self-consistent image; elf and macho emit a relocatable
+object (.text/.data sections, a symbol table and one PC32 relocation per
+static-symbol reference) that links with the system toolchain — references
+to symbols no GLOBL in the file defines become undefined external symbols.
+`)
+	out := fs.String("o", "", "write the output to this file")
+	format := fs.String("format", "raw", "output format: raw (concatenated image), elf or macho (relocatable object)")
 	fs.Parse(args)
 	if fs.NArg() != 1 {
-		fmt.Fprintln(os.Stderr, "usage: gasm asm [-o out.bin] <file>")
+		fmt.Fprintln(os.Stderr, "usage: gasm asm [--format raw|elf|macho] [-o out] <file>")
 		return 2
 	}
 	path := fs.Arg(0)
@@ -288,12 +428,35 @@ func cmdAsm(args []string) int {
 		}
 	}
 	if *out != "" {
-		all := img.Bytes()
-		if err := os.WriteFile(*out, all, 0o644); err != nil {
+		var obj []byte
+		var err error
+		var kind string
+		switch *format {
+		case "raw":
+			if len(img.Externals) > 0 {
+				fmt.Fprintf(os.Stderr, "gasm asm: external symbol %q needs an object file (use --format elf or --format macho)\n", img.Externals[0])
+				return 1
+			}
+			obj, kind = img.Bytes(), "raw image"
+		case "elf":
+			obj, err = img.ELFObject()
+			kind = "ELF object"
+		case "macho":
+			obj, err = img.MachOObject()
+			kind = "Mach-O object"
+		default:
+			fmt.Fprintf(os.Stderr, "gasm asm: unknown format %q (want raw, elf or macho)\n", *format)
+			return 2
+		}
+		if err != nil {
 			fmt.Fprintln(os.Stderr, "gasm asm:", err)
 			return 1
 		}
-		fmt.Printf("wrote %d bytes to %s\n", len(all), *out)
+		if err := os.WriteFile(*out, obj, 0o644); err != nil {
+			fmt.Fprintln(os.Stderr, "gasm asm:", err)
+			return 1
+		}
+		fmt.Printf("wrote %d bytes to %s (%s)\n", len(obj), *out, kind)
 	}
 	return 0
 }

cmd/gasm/main_test.go

@@ -52,6 +52,54 @@ func capture(fn func() int) (stdout, stderr string, code int) {
 	return string(ob), string(eb), code
 }
 
+// TestCmdFmtRecursive checks the go-fmt-style directory mode: with no
+// arguments every .s file below the working directory is formatted in place
+// ("." and "_" directories skipped), changed files are listed, and a second
+// run is a no-op.
+func TestCmdFmtRecursive(t *testing.T) {
+	tmp := t.TempDir()
+	t.Chdir(tmp)
+	unformatted := []byte("TEXT ·f(SB),NOSPLIT,$0\nRET\n")
+	write := func(path string) {
+		if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(path, unformatted, 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+	write("a_amd64.s")
+	write(filepath.Join("sub", "b_amd64.s"))
+	write(filepath.Join("_refs", "c_amd64.s"))
+	write(filepath.Join(".git", "d_amd64.s"))
+
+	out, errOut, code := capture(func() int { return cmdFmt(nil) })
+	if code != 0 {
+		t.Fatalf("code = %d (%s)", code, errOut)
+	}
+	if out != "a_amd64.s\n"+filepath.Join("sub", "b_amd64.s")+"\n" {
+		t.Errorf("listed files unexpected:\n%s", out)
+	}
+	for _, p := range []string{"a_amd64.s", filepath.Join("sub", "b_amd64.s")} {
+		b, _ := os.ReadFile(p)
+		if !strings.Contains(string(b), "\tRET") {
+			t.Errorf("%s not formatted in place:\n%s", p, b)
+		}
+	}
+	for _, p := range []string{filepath.Join("_refs", "c_amd64.s"), filepath.Join(".git", "d_amd64.s")} {
+		b, _ := os.ReadFile(p)
+		if string(b) != string(unformatted) {
+			t.Errorf("%s must not be touched:\n%s", p, b)
+		}
+	}
+
+	// Second pass: everything is canonical, nothing is listed.
+	out, _, code = capture(func() int { return cmdFmt(nil) })
+	if code != 0 || out != "" {
+		t.Errorf("second pass: code=%d out=%q, want a no-op", code, out)
+	}
+}
+
 func TestCmdTokens(t *testing.T) {
 	path := writeTemp(t, "f_amd64.s", clean)
 	out, _, code := capture(func() int { return cmdTokens([]string{path}) })
@@ -152,15 +200,32 @@ func TestCmdFmtWrite(t *testing.T) {
 func TestUsage(t *testing.T) {
 	var b bytes.Buffer
 	usage(&b)
-	if !strings.Contains(b.String(), "gasm") {
-		t.Errorf("usage text unexpected:\n%s", b.String())
+	out := b.String()
+	for _, want := range []string{
+		"gasm", "Commands:", "Flags:", "--help", "--version",
+		"tokens", "parse", "fmt", "lint", "asm", "lsp", "version",
+	} {
+		if !strings.Contains(out, want) {
+			t.Errorf("usage text missing %q:\n%s", want, out)
+		}
+	}
+}
+
+func TestCmdVersion(t *testing.T) {
+	out, _, code := capture(func() int { return cmdVersion() })
+	if code != 0 {
+		t.Fatalf("code = %d", code)
+	}
+	if !strings.Contains(out, version) {
+		t.Errorf("version output %q does not mention %q", out, version)
 	}
 }
 
 func TestCmdArgErrors(t *testing.T) {
-	// Missing file arguments produce a usage error (code 2).
-	if _, _, code := capture(func() int { return cmdFmt(nil) }); code != 2 {
-		t.Errorf("cmdFmt() code = %d, want 2", code)
+	// A missing path is an error (code 1); cmdFmt with no arguments is the
+	// recursive mode now, covered by TestCmdFmtRecursive.
+	if _, _, code := capture(func() int { return cmdFmt([]string{"no/such/path"}) }); code != 1 {
+		t.Errorf("cmdFmt(missing path) code = %d, want 1", code)
 	}
 	if _, _, code := capture(func() int { return cmdLint(nil) }); code != 2 {
 		t.Errorf("cmdLint() code = %d, want 2", code)

docs/ARCHITECTURE.md

@@ -142,7 +142,7 @@ Two deeper analyses sit on top of the AST:
   has no System V style callee-saved registers (amd64 `BX`, `R12`–`R15` and
   the like are caller-saved or permanent scratch, and hand-written kernels may
   clobber them freely).  The audited set is the frame pointer and the
-  goroutine pointer per architecture (amd64 `BP`/`R14`, arm64 `R18`/`R28`/
+  the frame pointer, the goroutine pointer per architecture (amd64 `BP`/`R14`, arm64 `R18`/`R28`/
   `R29`, riscv64 `X27`, loong64 `R22`); the goroutine pointer is reported only
   when the function can reach the runtime — it is not `NOSPLIT` or makes a
   call — since the ABI0 transition machinery restores it on those paths, and
@@ -157,9 +157,15 @@ Two deeper analyses sit on top of the AST:
 ### `format`
 
 The formatter works on the **token stream, not the AST**, so it preserves
-every line — comments and blanks included.  It only normalises indentation,
-operand spacing and per-function mnemonic alignment.  It is idempotent and its
-output always round-trips through the parser.
+every line — comments and blanks included.  It normalises indentation, operand
+spacing, per-function mnemonic alignment and blank-line layout: a new block
+(a label, `TEXT` or `GLOBL`) is preceded by exactly one blank line (comments
+leading a block stay with it), runs of blanks collapse to one, and a `RET`
+terminates the body so the next function's doc comment stays at column 0.  It
+is idempotent and its output always round-trips through the parser.  With a
+directory argument — or none — it reformats every `.s` file below it in
+place and lists the files changed, the way `go fmt` does (`.` and `_`
+directories are skipped).
 
 ### `lsp`
 
@@ -207,15 +213,26 @@ three-operand-plus-immediate form (`VSHUFPD`,
 `VPERM2I128`, `VINSERTI128`), the lane-extract form (`VEXTRACTI128`,
 `VEXTRACTF128`, where the YMM source occupies the reg field and the XMM or
 memory destination r/m), the direction-sensitive moves (`VMOVDQU`, `VMOVUPD`,
-`VMOVD`, `VMOVQ`, `VMOVSD`), the floating-point and FMA arithmetic (`VADDPD`,
-`VMULPD`, `VXORPD`, `VUNPCKHPD`, the scalar `VADDSD`/`VMULSD`, `VCVTDQ2PD`,
-`VFMADD231PD`) and the no-operand `VZEROUPPER` — together with `VPERMD` and
+`VMOVD`, `VMOVQ`, `VMOVSD`), the floating-point and FMA arithmetic — the
+packed double operations (`VADDPD`/`VSUBPD`/`VMULPD`/`VDIVPD`/`VMINPD`/
+`VMAXPD`), the unpacks (`VUNPCKHPD`/`VUNPCKLPD`), the scalar SD and SS
+operations, `VMOVDDUP`, `VXORPD`, the width-changing conversions
+(`VCVTDQ2PS`, `VCVTPS2PD`, `VCVTDQ2PD`, and the `VCVTPD2DQX`/`Y` and
+`VCVTTPD2DQX`/`Y` spellings, whose length follows the wider source) and
+`VFMADD231PD` — and the no-operand `VZEROUPPER`, together with `VPERMD` and
 the scalar families (`CMOVcc`, `SETcc`, `LZCNT`/`TZCNT`, the extending moves,
 `CVTSx2SD`, `IMUL3`) and the EVEX (AVX-512) prefix — the four-byte prefix with
-5-bit register fields (Z0–Z31, X/Y 16–31), opmask registers as operands and
-mask destinations, and the compressed disp8×N displacement, whose multiplier
-follows the memory operand's size — covering every instruction the go-flac
-AVX2 and AVX-512 kernels use.  Every encoding is validated two ways: by
+5-bit register fields (Z0–Z31, X/Y 16–31, with the mod=11 quirk that carries
+rm[4] in X̄), opmask registers (K0–K7 as operands, mask destinations and
+explicit merging/zeroing masks — written the way Go writes them, as a K
+operand among the operands plus a `.Z` mnemonic suffix), and the compressed
+disp8×N displacement, whose multiplier follows the memory operand's size —
+covering every instruction the go-flac and go-lz4 AVX2/AVX-512 kernels use,
+plus the common AVX-512 F/BW integer set and the floating-point and
+conversion set (the packed double arithmetic, the scalar SD/SS forms —
+whose EVEX encodings serve masked and zeroing use — `VMOVDDUP`, and the
+width-changing conversions, including the `VCVTPD2DQ`/`VCVTTPD2DQ` family
+whose length follows the wider source operand).  Every encoding is validated two ways: by
 round-trip decoding through `golang.org/x/arch`, and byte-for-byte against
 the machine code the real Go assembler emits — a comparison that holds for
 whole functions: all 27 functions of both kernels assemble to exactly the Go
@@ -226,9 +243,17 @@ File-level assembly (`AssembleFile`) goes beyond single functions: it
 materialises the file's static symbols (`GLOBL`/`DATA`) in a data section
 behind the code and resolves references to them (`mask<>(SB)`) to
 RIP-relative loads whose displacements point inside the resulting image, so
-the bytes are self-consistent at any base address.  External (non-file-local)
-symbols are rejected: they need object-file emission, which — together with
-EVEX masking/zeroing and the other architectures — is the rest of Phase 2.
+the bytes are self-consistent at any base address.  References to symbols no
+`GLOBL` defines are kept as relocations on the function layout, and the
+object-file emitters turn the whole image into a linkable object: the ELF
+and Mach-O writers (`gasm asm --format elf|macho`) lay the code and data out
+as `.text`/`.data` (or `__text`/`__data`) sections, export a symbol per
+`TEXT` and `GLOBL` (the `<>` ones local, the rest global) and emit one
+PC-relative relocation per static-symbol reference — undefined external
+symbols included, so the output links with the system toolchain.  GOOBJ
+emission, the format the Go linker consumes directly, is the remaining
+piece of Phase 2 (together with the rest of the EVEX set and the other
+architectures).
 
 ## Extension points
 

format/format.go

@@ -27,14 +27,6 @@ func Source(path, src string) string {
 		mnemLen int
 		funcID  int
 	}
-	const (
-		kBlank = iota
-		kComment
-		kPreproc
-		kDirective
-		kLabel
-		kInstr
-	)
 
 	infos := make([]info, len(lines))
 	funcID := -1
@@ -70,8 +62,8 @@ func Source(path, src string) string {
 		infos[i] = inf
 	}
 
-	// Second pass: render.
-	var b strings.Builder
+	// Second pass: render each line.
+	outs := make([]outLine, 0, len(lines))
 	inBody := false
 	for i, line := range lines {
 		inf := infos[i]
@@ -106,10 +98,87 @@ func Source(path, src string) string {
 				inBody = false
 			}
 		}
-		b.WriteString(strings.TrimRight(out, " \t"))
+		outs = append(outs, outLine{kind: inf.kind, text: strings.TrimRight(out, " \t")})
+	}
+	return normalizeSpacing(outs)
+}
+
+// Line classification, shared by the formatting passes.
+const (
+	kBlank = iota
+	kComment
+	kPreproc
+	kDirective
+	kLabel
+	kInstr
+)
+
+// outLine is one rendered line together with its classification.
+type outLine struct {
+	kind int
+	text string
+}
+
+// normalizeSpacing enforces the canonical blank-line layout: runs of blank
+// lines collapse to one, and a new block — a label, or a TEXT or GLOBL
+// directive — is preceded by exactly one blank line.  Comments immediately
+// above a block belong to it, so the blank line is inserted before them.  No
+// blank line is forced at the top of the file, right after a TEXT (the
+// function's first label), or between stacked labels that share an address.
+func normalizeSpacing(outs []outLine) string {
+	blockStart := func(ol outLine) bool {
+		switch ol.kind {
+		case kLabel:
+			return true
+		case kDirective:
+			// TEXT and GLOBL open a block; DATA continues a GLOBL block.
+			return strings.HasPrefix(ol.text, "TEXT") || strings.HasPrefix(ol.text, "GLOBL")
+		}
+		return false
+	}
+	insert := make([]bool, len(outs))
+	for i, ol := range outs {
+		if !blockStart(ol) {
+			continue
+		}
+		j := i
+		for j > 0 && outs[j-1].kind == kComment {
+			j--
+		}
+		if j == 0 {
+			continue // top of file
+		}
+		switch prev := outs[j-1]; {
+		case prev.kind == kBlank, prev.kind == kLabel:
+			continue // already separated, or stacked labels
+		case prev.kind == kDirective && strings.HasPrefix(prev.text, "TEXT"):
+			continue // the function's first label
+		}
+		insert[j] = true
+	}
+
+	var b strings.Builder
+	prevBlank := true // also suppresses leading blanks
+	for i, ol := range outs {
+		if insert[i] && !prevBlank {
 			b.WriteByte('\n')
 		}
-	return b.String()
+		if ol.kind == kBlank {
+			if !prevBlank {
+				b.WriteByte('\n')
+			}
+			prevBlank = true
+			continue
+		}
+		b.WriteString(ol.text)
+		b.WriteByte('\n')
+		prevBlank = false
+	}
+	out := strings.TrimRight(b.String(), "\n")
+	if out == "" {
+		return ""
+	}
+	return out + "\n"
 }
 
 // renderInstr renders an instruction line: a tab, the mnemonic padded to the

format/format_test.go

@@ -77,6 +77,64 @@ func TestDocCommentIndent(t *testing.T) {
 	}
 }
 
+// TestBlankLines checks the blank-line canonicalisation: exactly one blank
+// line before a new block (a label, or TEXT/GLOBL), runs of blanks collapsed
+// to one, and no blank forced after TEXT, between stacked labels, or at the
+// top of the file.  Leading comments belong to the block they precede.
+func TestBlankLines(t *testing.T) {
+	in := "#include \"textflag.h\"\n" +
+		"TEXT ·f(SB), NOSPLIT, $0\n" +
+		"first:\n" + // first label: no blank after TEXT
+		"XORQ AX, AX\n" +
+		"JMP next\n" + // unlabeled glue: fmt inserts a blank before next:
+		"next:\n" +
+		"stacked:\n" + // stacked labels share an address: no blank between
+		"INCQ AX\n" +
+		"\n" +
+		"\n" + // two blanks collapse to one
+		"// separated block\n" + // comment belongs to the label below
+		"later:\n" +
+		"RET\n" +
+		"// func g()\n" + // doc comment: blank goes before it
+		"TEXT ·g(SB), NOSPLIT, $0\n" +
+		"RET\n" +
+		"GLOBL ·mask(SB), RODATA, $8\n" + // blank before GLOBL…
+		"DATA ·mask+0(SB)/4, $1\n" + // …but not before DATA
+		"\n" +
+		"\n" +
+		"\n" // trailing blanks dropped
+
+	want := "#include \"textflag.h\"\n" +
+		"\n" +
+		"TEXT ·f(SB), NOSPLIT, $0\n" +
+		"first:\n" +
+		"\tXORQ AX, AX\n" +
+		"\tJMP  next\n" +
+		"\n" +
+		"next:\n" +
+		"stacked:\n" +
+		"\tINCQ AX\n" +
+		"\n" +
+		"\t// separated block\n" + // body comment before a label stays indented
+		"later:\n" +
+		"\tRET\n" +
+		"\n" +
+		"// func g()\n" +
+		"TEXT ·g(SB), NOSPLIT, $0\n" +
+		"\tRET\n" +
+		"\n" +
+		"GLOBL ·mask(SB), RODATA, $8\n" +
+		"DATA ·mask+0(SB)/4, $1\n"
+
+	got := Source("b_amd64.s", in)
+	if got != want {
+		t.Fatalf("formatting mismatch:\n--- got ---\n%q\n--- want ---\n%q", got, want)
+	}
+	if again := Source("b_amd64.s", got); again != got {
+		t.Fatalf("not idempotent:\n%q", again)
+	}
+}
+
 func TestOperandSpacing(t *testing.T) {
 	cases := map[string]string{
 		"4(SI)":           "4(SI)",

justfile

@@ -3,7 +3,7 @@
 
 # gasm-devkit — developer tooling for Go's Plan 9 assembler (GAsm).
 
-version := "0.6.0"
+version := "0.11.0"
 
 default:
     @just --list

lint/lint.go

@@ -242,7 +242,7 @@ func lintText(t *ast.Text, tab *arch.Table, archKnown bool, cfg Config, macros m
 				}
 			}
 
-			if archKnown && !cfg.Disable[CodeOperandCount] && !isMacroInvocation(mnem, macros) {
+			if archKnown && !cfg.Disable[CodeOperandCount] && !isMacroInvocation(mnem, macros) && !maskedEvex(mnem, st.Operands) {
 				if in, ok := tab.Lookup(mnem); ok && in.MinOps >= 0 {
 					n := len(st.Operands)
 					if n < in.MinOps || n > in.MaxOps {
@@ -438,6 +438,28 @@ func isMacroInvocation(mnem string, macros map[string]bool) bool {
 	return strings.Contains(mnem, "_") || macros[mnem]
 }
 
+// maskedEvex reports whether the instruction is a masked EVEX form: the
+// mnemonic carries a .Z suffix, or the operand list contains an opmask
+// register (K1–K7).  Either way the operand count differs from the unmasked
+// form, so count checks are skipped.
+func maskedEvex(mnem string, ops []*ast.Operand) bool {
+	if strings.Contains(mnem, ".") {
+		return true
+	}
+	for _, op := range ops {
+		if op.Kind == ast.OpAddr && op.Addr.Sym != nil && op.Addr.Base == "" &&
+			op.Addr.Index == "" && op.Addr.Sym.Pseudo == "" && isMaskReg(op.Addr.Sym.Name) {
+			return true
+		}
+	}
+	return false
+}
+
+// isMaskReg reports whether name is an opmask register K0–K7.
+func isMaskReg(name string) bool {
+	return len(name) == 2 && name[0] == 'K' && name[1] >= '0' && name[1] <= '7'
+}
+
 // isConditionalDirective reports whether a preprocessor directive (the text
 // after '#') is a conditional-compilation directive whose branches the parser
 // cannot resolve.

lint/lint_test.go

@@ -187,6 +187,26 @@ done:
 	}
 }
 
+// TestEvexMaskingRecognised checks that masked EVEX forms — the .Z suffix and
+// an explicit K operand — are recognised and exempt from operand-count
+// checks.
+func TestEvexMaskingRecognised(t *testing.T) {
+	diags := lintSrc(t, `
+#include "textflag.h"
+TEXT ·f(SB), NOSPLIT, $0
+	VPADDD.Z Z1, Z2, K2, Z3
+	VPMINSD Z1, Z2, K5, Z3
+	VMOVDQU8 Z1, K3, (SI)
+	RET
+`)
+	if codes(diags)[CodeUnknownInstr] != 0 {
+		t.Fatalf("masked EVEX must be recognised: %+v", diags)
+	}
+	if codes(diags)[CodeOperandCount] != 0 {
+		t.Fatalf("masked operand counts must not be flagged: %+v", diags)
+	}
+}
+
 func TestArm64AddressingSuffix(t *testing.T) {
 	// .W (pre-index) and .P (post-index) suffixes must resolve to the base
 	// instruction.