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