250 lines
6.3 KiB
Go
250 lines
6.3 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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"encoding/binary"
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"fmt"
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)
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// AArch64 ELF64 relocatable object emission.
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const (
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emAARCH64 = 183 // EM_AARCH64
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// AArch64 relocation types (the ELF psABI).
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rArm64PrelPgHi21 = 275 // R_AARCH64_ADR_PREL_PG_HI21 (ADRP page)
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rArm64AddAbsLo12NC = 277 // R_AARCH64_ADD_ABS_LO12_NC (ADD/STR/LDR page offset)
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rArm64Call26 = 283 // R_AARCH64_CALL26 (BL instruction)
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)
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// ELFAARCH64Object returns the image as an ELF64 relocatable object file for
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// AArch64 (EM_AARCH64, 64-bit, little-endian). The structure mirrors the
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// amd64 and RISC-V ELF emitters: .text, .data, .symtab, .strtab and an
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// optional .rela.text.
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func (img *Image) ELFAARCH64Object() ([]byte, error) {
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le := binary.LittleEndian
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const (
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secText = 1
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secData = 2
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)
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// Build symbol table.
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var locals, globals []elfSym
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for _, fn := range img.Funcs {
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s := elfSym{
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name: objectName(fn.Pkg, fn.Name),
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info: sttFunc,
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shndx: secText,
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value: uint64(fn.Offset),
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size: uint64(fn.Size),
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}
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if fn.Static {
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locals = append(locals, s)
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} else {
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s.info |= stbGlobal << stInfoShift
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globals = append(globals, s)
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}
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}
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for _, d := range img.DataSyms {
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s := elfSym{
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name: objectName(d.Pkg, d.Name),
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info: sttObject,
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shndx: secData,
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value: uint64(d.Offset),
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size: uint64(d.Size),
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}
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if d.Static {
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locals = append(locals, s)
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} else {
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s.info |= stbGlobal << stInfoShift
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globals = append(globals, s)
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}
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}
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for _, name := range img.Externals {
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globals = append(globals, elfSym{name: name, info: stbGlobal << stInfoShift})
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}
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syms := []elfSym{
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{},
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{name: ".text", info: sttSection, shndx: secText},
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{name: ".data", info: sttSection, shndx: secData},
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}
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syms = append(syms, locals...)
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shInfo := len(syms)
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syms = append(syms, globals...)
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symIdx := map[string]int{}
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for i, s := range syms {
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symIdx[s.name] = i
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}
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// Build relocations. Each SB reference is an ADRP pair:
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// ADRP Rd, 0 → R_AARCH64_ADR_PREL_PG_HI21
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// ADD/LDR/STR → R_AARCH64_ADD_ABS_LO12_NC
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type elfRela struct {
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off uint64
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typ uint32
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sym int
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addend int64
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}
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var relas []elfRela
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for _, fn := range img.Funcs {
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for _, r := range fn.Relocs {
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idx, ok := symIdx[r.Name]
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if !ok {
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return nil, fmt.Errorf("relocation references unknown symbol %q", r.Name)
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}
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var typ uint32
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switch {
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case r.Kind == RelArm64Branch:
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typ = rArm64Call26
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case r.Kind == RelArm64Addr && r.Off%4 == 4:
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typ = rArm64AddAbsLo12NC
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default:
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typ = rArm64PrelPgHi21
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}
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relas = append(relas, elfRela{
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off: uint64(fn.Offset + r.Off),
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typ: typ,
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sym: idx,
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addend: r.Addend - int64(r.After-r.Off),
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})
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}
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}
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// String tables.
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stNames := newElfStrtab()
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for _, s := range syms {
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stNames.add(s.name)
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}
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stSections := newElfStrtab()
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for _, n := range []string{".text", ".data", ".symtab", ".strtab", ".rela.text", ".shstrtab"} {
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stSections.add(n)
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}
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for _, n := range dwarfSectionNames {
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stSections.add(n)
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}
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hasRela := len(relas) > 0
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nSections := 6
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if hasRela {
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nSections = 7
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}
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secSymtab, secStrtab := 3, 4
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secShstr := nSections - 1
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// Layout.
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var out []byte
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out = append(out, make([]byte, 64)...)
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align := func(n int) {
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for len(out)%n != 0 {
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out = append(out, 0)
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}
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}
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align(16)
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textOff := len(out)
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out = append(out, img.Code...)
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align(16)
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dataOff := len(out)
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out = append(out, img.Data...)
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align(8)
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symtabOff := len(out)
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for _, s := range syms {
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var b [24]byte
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le.PutUint32(b[0:], uint32(stNames.at(s.name)))
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b[4] = s.info
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b[5] = 0
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le.PutUint16(b[6:], s.shndx)
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le.PutUint64(b[8:], s.value)
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le.PutUint64(b[16:], s.size)
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out = append(out, b[:]...)
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}
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strtabOff := len(out)
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out = append(out, stNames.bytes()...)
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var relaOff int
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if hasRela {
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align(8)
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relaOff = len(out)
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for _, r := range relas {
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var b [24]byte
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le.PutUint64(b[0:], r.off)
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le.PutUint64(b[8:], uint64(r.sym)<<32|uint64(r.typ))
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le.PutUint64(b[16:], uint64(r.addend))
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out = append(out, b[:]...)
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}
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}
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shstrOff := len(out)
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out = append(out, stSections.bytes()...)
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// DWARF debug sections.
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dwAlign := func(n int) {
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for len(out)%n != 0 {
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out = append(out, 0)
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}
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}
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dw := appendDWARFSections(&out, img, "gasm.s", symIdx, dwAlign)
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if dw != nil {
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nSections += 4
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}
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align(8)
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shoff := len(out)
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putSh := func(name string, typ int, flags uint64, off, size int, link, info int, alignV, entsize uint64) {
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var b [64]byte
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le.PutUint32(b[0:], uint32(stSections.at(name)))
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le.PutUint32(b[4:], uint32(typ))
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le.PutUint64(b[8:], flags)
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le.PutUint64(b[16:], 0)
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le.PutUint64(b[24:], uint64(off))
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le.PutUint64(b[32:], uint64(size))
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le.PutUint32(b[40:], uint32(link))
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le.PutUint32(b[44:], uint32(info))
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le.PutUint64(b[48:], alignV)
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le.PutUint64(b[56:], entsize)
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out = append(out, b[:]...)
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}
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putSh("", shtNull, 0, 0, 0, 0, 0, 0, 0)
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putSh(".text", shtProgbits, shfAlloc|shfExecInstr, textOff, len(img.Code), 0, 0, 16, 0)
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putSh(".data", shtProgbits, shfAlloc|shfWrite, dataOff, len(img.Data), 0, 0, 16, 0)
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putSh(".symtab", shtSymtab, 0, symtabOff, 24*len(syms), secStrtab, shInfo, 8, 24)
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putSh(".strtab", shtStrtab, 0, strtabOff, len(stNames.bytes()), 0, 0, 1, 0)
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if hasRela {
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putSh(".rela.text", shtRela, 0, relaOff, 24*len(relas), secSymtab, secText, 8, 24)
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}
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putSh(".shstrtab", shtStrtab, 0, shstrOff, len(stSections.bytes()), 0, 0, 1, 0)
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if dw != nil {
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putSh(".debug_abbrev", shtProgbits, 0, dw.abbrevOff, dw.abbrevSize, 0, 0, 1, 0)
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putSh(".debug_info", shtProgbits, 0, dw.infoOff, dw.infoSize, 0, 0, 1, 0)
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putSh(".debug_line", shtProgbits, 0, dw.lineOff, dw.lineSize, 0, 0, 1, 0)
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putSh(".debug_line_str", shtProgbits, 0, dw.lineStrOff, dw.lineStrSize, 0, 0, 1, 0)
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}
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// ELF header.
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hdr := out[:64]
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copy(hdr[0:], []byte{0x7f, 'E', 'L', 'F', elfClass64, elfDataLSB, elfVersion, 0})
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le.PutUint16(hdr[16:], etREL)
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le.PutUint16(hdr[18:], emAARCH64)
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le.PutUint32(hdr[20:], elfVersion)
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le.PutUint64(hdr[24:], 0)
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le.PutUint64(hdr[32:], 0)
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le.PutUint64(hdr[40:], uint64(shoff))
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le.PutUint32(hdr[48:], 0)
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le.PutUint16(hdr[52:], 64)
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le.PutUint16(hdr[54:], 0)
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le.PutUint16(hdr[56:], 0)
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le.PutUint16(hdr[58:], 64)
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le.PutUint16(hdr[60:], uint16(nSections))
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le.PutUint16(hdr[62:], uint16(secShstr))
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return out, nil
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}
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