fix(asm): encode RISC-V CALL sym(SB) as JAL

Assisted-by: DeepSeek V4 Pro

CHANGELOG.md

@@ -82,6 +82,14 @@ Unreleased changes on the `development` branch.
   encoders were removed, and the `C.LUI` direct-instruction compression now
   uses the correct six-bit signed range.  A byte-exact ground-truth test
   covers the branch family and jumps against `GOARCH=riscv64 go tool asm`.
+- **RISC-V `CALL sym(SB)`.**  The call pseudo-instruction now emits the
+  toolchain's `JAL X1, sym(SB)` with a single `R_RISCV_JAL` relocation
+  (previously it emitted an `AUIPC`+`JALR` pair against a local branch
+  label, a form `go tool asm` rejects).  The GOOBJ and ELF emitters now map
+  that relocation (Go objabi 59 / ELF `R_RISCV_JAL` 17, a 4-byte field), and
+  relocation offsets are recorded relative to the function start (including
+  the prologue).  A byte-exact ground-truth test covers a call against
+  `GOARCH=riscv64 go tool asm`.
 - **Debugger watchpoint slots.**  `gasm debug`'s `watch` command always used
   hardware watchpoint slot 0, so a second `watch` call silently overwrote
   the first.  Watchpoint slots are now tracked in the `Session` (DR0–DR3);

asm/elfriscv.go

@@ -15,6 +15,7 @@ const (
 
 	// RISC-V relocation types.
 	rRISCV32         = 1
+	rRISCVJAL        = 17 // R_RISCV_JAL
 	rRISCVPCRELHI20  = 23 // R_RISCV_PCREL_HI20
 	rRISCVPCRELLO12I = 24 // R_RISCV_PCREL_LO12_I
 	rRISCVPCRELLO12S = 25 // R_RISCV_PCREL_LO12_S
@@ -109,6 +110,8 @@ func (img *Image) ELFRISCVObject() ([]byte, error) {
 					elfRela{off: uint64(fn.Offset + r.Off), typ: rRISCVPCRELHI20, sym: idx, addend: r.Addend},
 					elfRela{off: uint64(fn.Offset + r.Off + 4), typ: rRISCVPCRELLO12S, sym: idx, addend: 0},
 				)
+			case RelRISCVJal:
+				relas = append(relas, elfRela{off: uint64(fn.Offset + r.Off), typ: rRISCVJAL, sym: idx, addend: r.Addend})
 			case RelPCRelAbs:
 				relas = append(relas, elfRela{off: uint64(fn.Offset + r.Off), typ: rRISCV32, sym: idx, addend: r.Addend})
 			default:

asm/goobjriscv.go

@@ -25,17 +25,22 @@ func (img *Image) GOObjectRISCV(pkgPath, srcPath string) ([]byte, error) {
 		return nil, err
 	}
 	return img.emitGOObject(pkgPath, srcPath, pre, 2, func(r Reloc) (uint16, uint8) {
-		if r.Kind == RelRISCVPCRELSType {
+		switch r.Kind {
+		case RelRISCVPCRELSType:
 			return relocRISCVPcrelStype, 8
+		case RelRISCVJal:
+			return relocRISCVJal, 4
+		default:
+			return relocRISCVPcrelItype, 8
 		}
-		return relocRISCVPcrelItype, 8
 	})
 }
 
 // RISC-V relocation types (cmd/internal/objabi).  The Go linker applies
 // R_RISCV_PCREL_ITYPE/STYPE to an AUIPC + I/S-type instruction pair as a
-// single 8-byte field.
+// single 8-byte field; R_RISCV_JAL covers a single 4-byte J-type instruction.
 const (
+	relocRISCVJal        = 59 // R_RISCV_JAL
 	relocRISCVPcrelItype = 62 // R_RISCV_PCREL_ITYPE
 	relocRISCVPcrelStype = 63 // R_RISCV_PCREL_STYPE
 )

asm/link.go

@@ -92,6 +92,7 @@ const (
 	RelPCRel32         RelocKind = iota // 32-bit PC-relative (amd64)
 	RelRISCVPCRELIType                  // R_RISCV_PCREL_ITYPE (AUIPC + I-type pair)
 	RelRISCVPCRELSType                  // R_RISCV_PCREL_STYPE (AUIPC + S-type pair)
+	RelRISCVJal                         // R_RISCV_JAL (J-type call)
 	RelPCRelAbs                         // 32-bit absolute (R_RISCV_32)
 	RelLoong64AddrHi                    // R_LOONG64_ADDR_HI (pcalau12i)
 	RelLoong64AddrLo                    // R_LOONG64_ADDR_LO (addi.d/ld/st)

asm/riscv_assemble.go

@@ -100,13 +100,14 @@ func assembleRISCV(t *ast.Text) ([]byte, map[string]int, []Reloc, []LineEntry, [
 			if c16, ok := tryCompressRVC(r.instr, fi); ok {
 				code = []byte{byte(c16), byte(c16 >> 8)}
 			}
-			// Make newly added relocation offsets absolute (subtract prologue to make
+			// Make newly added relocation offsets function-relative.  Each
-			// them function-relative, then the caller adds fn.Offset).  After
+			// instruction records its reloc offset relative to its own start;
-			// points just past the AUIPC+second-instruction pair, which is
+			// the current pc is that instruction's offset from the function
-			// always 8 bytes wide for these static-symbol references.
+			// start (which includes the prologue).  After is the address just
+			// past the relocated field, shifted by the same amount.
 			for j := preCount; j < len(relocs); j++ {
-				relocs[j].Off += pc - len(prologue)
+				relocs[j].Off += pc
-				relocs[j].After = relocs[j].Off + 8
+				relocs[j].After += pc
 			}
 			preCount = len(relocs)
 			// The RET's epilogue closes the frame: the SP delta returns to zero
@@ -175,32 +176,23 @@ func encodeRISCVInstr(instr *ast.Instr, pc int, offsets map[string]int, fi riscv
 	// Handle pseudo-instructions and special cases first.
 	switch mnem {
 	case "RET":
-		// RET = epilogue (restore LR and close the frame when present) + C.JR ra.
+		// RET = epilogue (restore LR and close the frame when present) +
+		// uncompressed JALR X0, 0(X1) (the toolchain never compresses RET).
 		return riscvReturn(fi), nil
 	case "CALL":
-		// CALL target → AUIPC X1, %pcrel_hi + JALR X1, %pcrel_lo(X1).
+		// CALL sym(SB) → JAL X1, sym(SB) with a single R_RISCV_JAL
-		// For now, emit AUIPC X1, 0 + JALR X1, 0(X1) with zero offsets.
+		// relocation.  The Go assembler rejects CALL to a local branch label.
-		// The relocation system will fill the actual offsets.
+		if len(ops) != 1 {
-		if len(ops) >= 1 {
+			return nil, fmt.Errorf("CALL expects 1 operand, got %d", len(ops))
-			target := labelFromOperand(ops[0])
-			targetOff, ok := offsets[target]
-			if !ok {
-				return nil, fmt.Errorf("undefined label %q%s", target, suggestLabel(target, offsets))
-			}
-			offset := int32(targetOff - pc)
-			// AUIPC X1, upper 20 bits
-			hi := (offset + 0x800) >> 12
-			word1 := riscvUType(riscvEnc{0x17, 0x0, 0x00}, 1, hi<<12)
-			// JALR X1, lower 12 bits(X1)
-			lo := offset - (hi << 12)
-			word2 := riscvIType(riscvEnc{0x67, 0x0, 0x00}, 1, 1, lo)
-			var out []byte
-			out = append(out, byte(word1), byte(word1>>8), byte(word1>>16), byte(word1>>24))
-			out = append(out, byte(word2), byte(word2>>8), byte(word2>>16), byte(word2>>24))
-			return out, nil
 		}
-		// CALL with no target: encode as NOP (unsupported).
+		op := ops[0]
-		word = riscvIType(riscvEnc{0x13, 0x0, 0x00}, 0, 0, 0)
+		if op.Addr.Sym == nil || op.Addr.Sym.Pseudo != "SB" {
+			return nil, fmt.Errorf("CALL: local branch target is not supported (use CALL sym(SB))")
+		}
+		if relocs != nil {
+			*relocs = append(*relocs, Reloc{Off: 0, After: 4, Name: op.Addr.Sym.Name, Kind: RelRISCVJal, Addend: op.Addr.Sym.Offset})
+		}
+		word = riscvJType(1, 0) // JAL X1, 0 — the linker fills the offset
 		return []byte{byte(word), byte(word >> 8), byte(word >> 16), byte(word >> 24)}, nil
 	case "JMP":
 		// JMP = JAL X0, target.  The Go assembler never compresses this to

asm/riscv_encode_test.go

@@ -4,6 +4,7 @@
 package asm
 
 import (
+	"bytes"
 	"testing"
 
 	"sourcedock.dev/petrbalvin/gasm-devkit/ast"
@@ -720,19 +721,43 @@ TEXT ·badfp(SB), NOSPLIT, $0
 }
 
 func TestRISCV_CALL(t *testing.T) {
-	// CALL target → AUIPC + JALR (8 bytes).
+	// CALL sym(SB) → JAL X1, sym(SB) with a single R_RISCV_JAL relocation.
 	fn := firstTextRISCV(t, `#include "textflag.h"
 TEXT ·calltest(SB), NOSPLIT, $0
-	CALL sub
+	CALL ext(SB)
-done:
 	RET
+`)
+	code, _, relocs, _, _, err := assembleRISCV(fn)
+	if err != nil {
+		t.Fatalf("assemble: %v", err)
+	}
+	// prologue (8) + JAL (4) + epilogue+JALR (8) = 20
+	if len(code) != 20 {
+		t.Fatalf("expected 20 bytes with CALL sym(SB), got %d", len(code))
+	}
+	if len(relocs) != 1 {
+		t.Fatalf("relocs = %d, want 1", len(relocs))
+	}
+	r := relocs[0]
+	if r.Kind != RelRISCVJal || r.Name != "ext" || r.Off != 8 || r.After != 12 || r.Addend != 0 {
+		t.Errorf("reloc = {kind %v off %d after %d name %q addend %d}", r.Kind, r.Off, r.After, r.Name, r.Addend)
+	}
+	// The JAL instruction itself is JAL X1, 0 at function offset 8.
+	wantJAL := wordLE(riscvJType(1, 0))
+	if !bytes.Equal(code[8:12], wantJAL) {
+		t.Errorf("JAL = % x, want % x", code[8:12], wantJAL)
+	}
+}
+
+func TestRISCV_CALL_local_error(t *testing.T) {
+	fn := firstTextRISCV(t, `#include "textflag.h"
+TEXT ·calllocal(SB), NOSPLIT, $0
+	CALL sub
 sub:
 	RET
 `)
-	code := assembleRISCVHelper(t, fn)
+	_, _, _, _, _, err := assembleRISCV(fn)
-	// A zero-frame non-leaf function saves LR: prologue (8) + CALL (8) +
+	if err == nil {
-	// two framed RETs (8 each) = 32.
+		t.Error("expected error for CALL to local label, got nil")
-	if len(code) != 32 {
-		t.Errorf("expected 32 bytes with CALL, got %d", len(code))
 	}
 }

asm/riscv_goobj_test.go

@@ -5,6 +5,7 @@ package asm
 
 import (
 	"bytes"
+	"debug/elf"
 	"encoding/binary"
 	"os"
 	"os/exec"
@@ -15,10 +16,64 @@ import (
 	"sourcedock.dev/petrbalvin/gasm-devkit/parser"
 )
 
-// TestGOObjectRISCVStructure checks the emitted RISC-V object's relocations:
+// TestGOObjectRISCVCallReloc checks that CALL sym(SB) emits a single JAL
-// each AUIPC + second-instruction pair carries a single 8-byte
+// instruction carrying an R_RISCV_JAL relocation (4-byte field) in both the
-// R_RISCV_PCREL_ITYPE/STYPE relocation, exactly as `go tool asm` models it
+// GOOBJ and ELF object emitters.
-// (rather than the ELF HI20/LO12 pair).
+func TestGOObjectRISCVCallReloc(t *testing.T) {
+	f, errs := parser.Parse("k_riscv64.s", `
+#include "textflag.h"
+
+TEXT ·c(SB), NOSPLIT, $0-0
+	CALL callee<>(SB)
+	RET
+
+GLOBL callee<>(SB), RODATA, $8
+DATA callee<>+0(SB)/8, $42
+`)
+	if len(errs) > 0 {
+		t.Fatalf("parse: %v", errs)
+	}
+	img, err := AssembleFileRISCV(f)
+	if err != nil {
+		t.Fatalf("AssembleFileRISCV: %v", err)
+	}
+	fn := img.Funcs[0]
+	if len(fn.Relocs) != 1 {
+		t.Fatalf("relocs = %d, want 1", len(fn.Relocs))
+	}
+	r := fn.Relocs[0]
+	if r.Kind != RelRISCVJal || r.Off != 8 || r.After != 12 || r.Name != "callee" || r.Addend != 0 || r.External {
+		t.Errorf("reloc = {kind %v off %d after %d name %q addend %d external %v}", r.Kind, r.Off, r.After, r.Name, r.Addend, r.External)
+	}
+
+	obj, err := img.GOObjectRISCV("testpkg", "k_riscv64.s")
+	if err != nil {
+		t.Fatalf("GOObjectRISCV: %v", err)
+	}
+	v := openGoobj(t, obj)
+	relocIdx := v.blk(blkRelocIdx)
+	relocs := v.blk(blkReloc)
+	// The function is the last non-package symbol: 4 package defs, then the
+	// 4 pc tables and the function.
+	first := int(binary.LittleEndian.Uint32(relocIdx[(4+4)*4:]))
+	if (first+1)*23 > len(relocs) {
+		t.Fatalf("reloc block too short: first=%d len=%d", first, len(relocs))
+	}
+	e := relocs[first*23:]
+	le := binary.LittleEndian
+	if int32(le.Uint32(e[0:])) != 8 || e[4] != 4 || le.Uint16(e[5:]) != relocRISCVJal || le.Uint32(e[15:]) != pkgIdxSelf || le.Uint32(e[19:]) != 0 {
+		t.Errorf("GOOBJ reloc = off %d size %d type %d pkg %d sym %d", int32(le.Uint32(e[0:])), e[4], le.Uint16(e[5:]), le.Uint32(e[15:]), le.Uint32(e[19:]))
+	}
+
+	// The ELF object must carry a single R_RISCV_JAL relocation in .rela.text.
+	elfObj, err := img.ELFRISCVObject()
+	if err != nil {
+		t.Fatalf("ELFRISCVObject: %v", err)
+	}
+	if !hasELFRISCVJAL(t, elfObj) {
+		t.Error("ELF object missing R_RISCV_JAL relocation")
+	}
+}
 func TestGOObjectRISCVStructure(t *testing.T) {
 	f, errs := parser.Parse("k_riscv64.s", `
 #include "textflag.h"
@@ -262,3 +317,30 @@ func main() {
 		t.Errorf("main.add not found in linked binary:\n%s", nmOut)
 	}
 }
+
+// hasELFRISCVJAL reports whether the ELF object carries an R_RISCV_JAL
+// relocation in its .rela.text section.
+func hasELFRISCVJAL(t *testing.T, data []byte) bool {
+	t.Helper()
+	f, err := elf.NewFile(bytes.NewReader(data))
+	if err != nil {
+		t.Fatalf("parse ELF: %v", err)
+	}
+	defer f.Close()
+	rela := f.Section(".rela.text")
+	if rela == nil {
+		return false
+	}
+	b, err := rela.Data()
+	if err != nil {
+		t.Fatalf(".rela.text data: %v", err)
+	}
+	const rRISCVJAL = 17
+	for i := 0; i+24 <= len(b); i += 24 {
+		info := binary.LittleEndian.Uint64(b[i+8:])
+		if uint32(info) == rRISCVJAL {
+			return true
+		}
+	}
+	return false
+}

testdata/verify/call_riscv64.s

@@ -0,0 +1,8 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "textflag.h"
+
+TEXT ·call(SB), NOSPLIT, $0
+	CALL callee(SB)
+	RET

verify/riscv_groundtruth_test.go

@@ -24,6 +24,7 @@ func TestGroundTruthRISCV(t *testing.T) {
 		"../testdata/verify/largeimm_riscv64.s",
 		"../testdata/verify/movimm_riscv64.s",
 		"../testdata/verify/branch_riscv64.s",
+		"../testdata/verify/call_riscv64.s",
 	} {
 		t.Run(path, func(t *testing.T) {
 			testGroundTruthRISCVFile(t, path)