96 lines
3.0 KiB
Go
96 lines
3.0 KiB
Go
// 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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"fmt"
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"os"
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"os/exec"
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"path/filepath"
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"sync"
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)
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// GOObjectRISCV emits a GOOBJ object file for RISC-V. The layout is the
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// shared one in goobj.go — the toolchain preamble, the go120ld header with
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// its block offsets, the string table, the symbol definitions and the
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// reloc/aux/data index arrays — with the RISC-V preamble, the MinLC of 2 for
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// the pc-value deltas, and the single R_RISCV_PCREL_ITYPE/STYPE relocation
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// per AUIPC pair, matching `go tool asm`'s model (each pair is one 8-byte
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// relocation, not the ELF HI20/LO12 pair).
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func (img *Image) GOObjectRISCV(pkgPath, srcPath string) ([]byte, error) {
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pre, err := toolchainObjectPreambleRISCV()
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if err != nil {
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return nil, err
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}
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return img.emitGOObject(pkgPath, srcPath, pre, 2, func(r Reloc) (uint16, uint8) {
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switch r.Kind {
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case RelRISCVPCRELSType:
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return relocRISCVPcrelStype, 8
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case RelRISCVJal:
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return relocRISCVJal, 4
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default:
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return relocRISCVPcrelItype, 8
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}
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})
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}
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// RISC-V relocation types (cmd/internal/objabi). The Go linker applies
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// R_RISCV_PCREL_ITYPE/STYPE to an AUIPC + I/S-type instruction pair as a
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// single 8-byte field; R_RISCV_JAL covers a single 4-byte J-type instruction.
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const (
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relocRISCVJal = 59 // R_RISCV_JAL
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relocRISCVPcrelItype = 62 // R_RISCV_PCREL_ITYPE
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relocRISCVPcrelStype = 63 // R_RISCV_PCREL_STYPE
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)
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// toolchainObjectPreambleRISCV returns the "go object ...\n!\n" header
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// the installed go tool asm writes for riscv64, captured by assembling a
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// one-instruction probe (see toolchainObjectPreamble).
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var (
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preambleRISCVOnce sync.Once
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preambleRISCV []byte
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preambleRISCVErr error
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)
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func toolchainObjectPreambleRISCV() ([]byte, error) {
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preambleRISCVOnce.Do(func() {
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goBin, err := exec.LookPath("go")
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if err != nil {
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preambleRISCVErr = fmt.Errorf("GOOBJ emission needs the Go toolchain: %w", err)
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return
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}
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dir, err := os.MkdirTemp("", "gasm-preamble-riscv")
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if err != nil {
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preambleRISCVErr = err
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return
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}
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defer os.RemoveAll(dir)
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src := filepath.Join(dir, "probe_riscv64.s")
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if err := os.WriteFile(src, []byte("TEXT \u00b7x(SB), $0-0\n\tRET\n"), 0o644); err != nil {
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preambleRISCVErr = err
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return
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}
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obj := filepath.Join(dir, "probe.o")
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cmd := exec.Command(goBin, "tool", "asm", "-p", "probe", "-o", obj, src)
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cmd.Env = append(os.Environ(), "GOARCH=riscv64")
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if out, err := cmd.CombinedOutput(); err != nil {
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preambleRISCVErr = fmt.Errorf("probing the assembler for the object header: %v\n%s", err, out)
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return
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}
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data, err := os.ReadFile(obj)
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if err != nil {
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preambleRISCVErr = err
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return
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}
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i := bytes.Index(data, []byte("\n!\n"))
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if i < 0 || !bytes.HasPrefix(data[i+3:], []byte(goobjMagic)) {
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preambleRISCVErr = fmt.Errorf("unrecognised assembler object layout")
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return
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}
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preambleRISCV = data[:i+3]
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})
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return preambleRISCV, preambleRISCVErr
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}
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