go asm 源码
golang asm 代码
文件路径：/src/cmd/link/internal/amd64/asm.go
// Inferno utils/6l/asm.c
// https://bitbucket.org/inferno-os/inferno-os/src/master/utils/6l/asm.c
//
// Copyright © 1994-1999 Lucent Technologies Inc. All rights reserved.
// Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
// Portions Copyright © 1997-1999 Vita Nuova Limited
// Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
// Portions Copyright © 2004,2006 Bruce Ellis
// Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
// Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
// Portions Copyright © 2009 The Go Authors. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package amd64
import (
"cmd/internal/objabi"
"cmd/internal/sys"
"cmd/link/internal/ld"
"cmd/link/internal/loader"
"cmd/link/internal/sym"
"debug/elf"
"log"
)
func PADDR(x uint32) uint32 {
return x &^ 0x80000000
}
func gentext(ctxt *ld.Link, ldr *loader.Loader) {
initfunc, addmoduledata := ld.PrepareAddmoduledata(ctxt)
if initfunc == nil {
return
}
o := func(op ...uint8) {
for _, op1 := range op {
initfunc.AddUint8(op1)
}
}
// 0000000000000000 <local.dso_init>:
// 0: 48 8d 3d 00 00 00 00 lea 0x0(%rip),%rdi # 7 <local.dso_init+0x7>
// 3: R_X86_64_PC32 runtime.firstmoduledata-0x4
o(0x48, 0x8d, 0x3d)
initfunc.AddPCRelPlus(ctxt.Arch, ctxt.Moduledata, 0)
// 7: e8 00 00 00 00 callq c <local.dso_init+0xc>
// 8: R_X86_64_PLT32 runtime.addmoduledata-0x4
o(0xe8)
initfunc.AddSymRef(ctxt.Arch, addmoduledata, 0, objabi.R_CALL, 4)
// c: c3 retq
o(0xc3)
}
func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym, r loader.Reloc, rIdx int) bool {
targ := r.Sym()
var targType sym.SymKind
if targ != 0 {
targType = ldr.SymType(targ)
}
switch rt := r.Type(); rt {
default:
if rt >= objabi.ElfRelocOffset {
ldr.Errorf(s, "unexpected relocation type %d (%s)", r.Type(), sym.RelocName(target.Arch, r.Type()))
return false
}
// Handle relocations found in ELF object files.
case objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_PC32):
if targType == sym.SDYNIMPORT {
ldr.Errorf(s, "unexpected R_X86_64_PC32 relocation for dynamic symbol %s", ldr.SymName(targ))
}
if targType == 0 || targType == sym.SXREF {
ldr.Errorf(s, "unknown symbol %s in pcrel", ldr.SymName(targ))
}
su := ldr.MakeSymbolUpdater(s)
su.SetRelocType(rIdx, objabi.R_PCREL)
su.SetRelocAdd(rIdx, r.Add()+4)
return true
case objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_PC64):
if targType == sym.SDYNIMPORT {
ldr.Errorf(s, "unexpected R_X86_64_PC64 relocation for dynamic symbol %s", ldr.SymName(targ))
}
if targType == 0 || targType == sym.SXREF {
ldr.Errorf(s, "unknown symbol %s in pcrel", ldr.SymName(targ))
}
su := ldr.MakeSymbolUpdater(s)
su.SetRelocType(rIdx, objabi.R_PCREL)
su.SetRelocAdd(rIdx, r.Add()+8)
return true
case objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_PLT32):
su := ldr.MakeSymbolUpdater(s)
su.SetRelocType(rIdx, objabi.R_PCREL)
su.SetRelocAdd(rIdx, r.Add()+4)
if targType == sym.SDYNIMPORT {
addpltsym(target, ldr, syms, targ)
su.SetRelocSym(rIdx, syms.PLT)
su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymPlt(targ)))
}
return true
case objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_GOTPCREL),
objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_GOTPCRELX),
objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_REX_GOTPCRELX):
su := ldr.MakeSymbolUpdater(s)
if targType != sym.SDYNIMPORT {
// have symbol
sData := ldr.Data(s)
if r.Off() >= 2 && sData[r.Off()-2] == 0x8b {
su.MakeWritable()
// turn MOVQ of GOT entry into LEAQ of symbol itself
writeableData := su.Data()
writeableData[r.Off()-2] = 0x8d
su.SetRelocType(rIdx, objabi.R_PCREL)
su.SetRelocAdd(rIdx, r.Add()+4)
return true
}
}
// fall back to using GOT and hope for the best (CMOV*)
// TODO: just needs relocation, no need to put in .dynsym
ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_X86_64_GLOB_DAT))
su.SetRelocType(rIdx, objabi.R_PCREL)
su.SetRelocSym(rIdx, syms.GOT)
su.SetRelocAdd(rIdx, r.Add()+4+int64(ldr.SymGot(targ)))
return true
case objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_64):
if targType == sym.SDYNIMPORT {
ldr.Errorf(s, "unexpected R_X86_64_64 relocation for dynamic symbol %s", ldr.SymName(targ))
}
su := ldr.MakeSymbolUpdater(s)
su.SetRelocType(rIdx, objabi.R_ADDR)
if target.IsPIE() && target.IsInternal() {
// For internal linking PIE, this R_ADDR relocation cannot
// be resolved statically. We need to generate a dynamic
// relocation. Let the code below handle it.
break
}
return true
// Handle relocations found in Mach-O object files.
case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 0,
objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED*2 + 0,
objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_BRANCH*2 + 0:
su := ldr.MakeSymbolUpdater(s)
su.SetRelocType(rIdx, objabi.R_ADDR)
if targType == sym.SDYNIMPORT {
ldr.Errorf(s, "unexpected reloc for dynamic symbol %s", ldr.SymName(targ))
}
if target.IsPIE() && target.IsInternal() {
// For internal linking PIE, this R_ADDR relocation cannot
// be resolved statically. We need to generate a dynamic
// relocation. Let the code below handle it.
if rt == objabi.MachoRelocOffset+ld.MACHO_X86_64_RELOC_UNSIGNED*2 {
break
} else {
// MACHO_X86_64_RELOC_SIGNED or MACHO_X86_64_RELOC_BRANCH
// Can this happen? The object is expected to be PIC.
ldr.Errorf(s, "unsupported relocation for PIE: %v", rt)
}
}
return true
case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_BRANCH*2 + 1:
if targType == sym.SDYNIMPORT {
addpltsym(target, ldr, syms, targ)
su := ldr.MakeSymbolUpdater(s)
su.SetRelocSym(rIdx, syms.PLT)
su.SetRelocType(rIdx, objabi.R_PCREL)
su.SetRelocAdd(rIdx, int64(ldr.SymPlt(targ)))
return true
}
fallthrough
case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 1,
objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED*2 + 1,
objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED_1*2 + 1,
objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED_2*2 + 1,
objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED_4*2 + 1:
su := ldr.MakeSymbolUpdater(s)
su.SetRelocType(rIdx, objabi.R_PCREL)
if targType == sym.SDYNIMPORT {
ldr.Errorf(s, "unexpected pc-relative reloc for dynamic symbol %s", ldr.SymName(targ))
}
return true
case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_GOT_LOAD*2 + 1:
if targType != sym.SDYNIMPORT {
// have symbol
// turn MOVQ of GOT entry into LEAQ of symbol itself
sdata := ldr.Data(s)
if r.Off() < 2 || sdata[r.Off()-2] != 0x8b {
ldr.Errorf(s, "unexpected GOT_LOAD reloc for non-dynamic symbol %s", ldr.SymName(targ))
return false
}
su := ldr.MakeSymbolUpdater(s)
su.MakeWritable()
sdata = su.Data()
sdata[r.Off()-2] = 0x8d
su.SetRelocType(rIdx, objabi.R_PCREL)
return true
}
fallthrough
case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_GOT*2 + 1:
if targType != sym.SDYNIMPORT {
ldr.Errorf(s, "unexpected GOT reloc for non-dynamic symbol %s", ldr.SymName(targ))
}
ld.AddGotSym(target, ldr, syms, targ, 0)
su := ldr.MakeSymbolUpdater(s)
su.SetRelocType(rIdx, objabi.R_PCREL)
su.SetRelocSym(rIdx, syms.GOT)
su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ)))
return true
}
// Reread the reloc to incorporate any changes in type above.
relocs := ldr.Relocs(s)
r = relocs.At(rIdx)
switch r.Type() {
case objabi.R_CALL,
objabi.R_PCREL:
if targType != sym.SDYNIMPORT {
// nothing to do, the relocation will be laid out in reloc
return true
}
if target.IsExternal() {
// External linker will do this relocation.
return true
}
// Internal linking, for both ELF and Mach-O.
// Build a PLT entry and change the relocation target to that entry.
addpltsym(target, ldr, syms, targ)
su := ldr.MakeSymbolUpdater(s)
su.SetRelocSym(rIdx, syms.PLT)
su.SetRelocAdd(rIdx, int64(ldr.SymPlt(targ)))
return true
case objabi.R_ADDR:
if ldr.SymType(s) == sym.STEXT && target.IsElf() {
su := ldr.MakeSymbolUpdater(s)
if target.IsSolaris() {
addpltsym(target, ldr, syms, targ)
su.SetRelocSym(rIdx, syms.PLT)
su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymPlt(targ)))
return true
}
// The code is asking for the address of an external
// function. We provide it with the address of the
// correspondent GOT symbol.
ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_X86_64_GLOB_DAT))
su.SetRelocSym(rIdx, syms.GOT)
su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ)))
return true
}
// Process dynamic relocations for the data sections.
if target.IsPIE() && target.IsInternal() {
// When internally linking, generate dynamic relocations
// for all typical R_ADDR relocations. The exception
// are those R_ADDR that are created as part of generating
// the dynamic relocations and must be resolved statically.
//
// There are three phases relevant to understanding this:
//
// dodata() // we are here
// address() // symbol address assignment
// reloc() // resolution of static R_ADDR relocs
//
// At this point symbol addresses have not been
// assigned yet (as the final size of the .rela section
// will affect the addresses), and so we cannot write
// the Elf64_Rela.r_offset now. Instead we delay it
// until after the 'address' phase of the linker is
// complete. We do this via Addaddrplus, which creates
// a new R_ADDR relocation which will be resolved in
// the 'reloc' phase.
//
// These synthetic static R_ADDR relocs must be skipped
// now, or else we will be caught in an infinite loop
// of generating synthetic relocs for our synthetic
// relocs.
//
// Furthermore, the rela sections contain dynamic
// relocations with R_ADDR relocations on
// Elf64_Rela.r_offset. This field should contain the
// symbol offset as determined by reloc(), not the
// final dynamically linked address as a dynamic
// relocation would provide.
switch ldr.SymName(s) {
case ".dynsym", ".rela", ".rela.plt", ".got.plt", ".dynamic":
return false
}
} else {
// Either internally linking a static executable,
// in which case we can resolve these relocations
// statically in the 'reloc' phase, or externally
// linking, in which case the relocation will be
// prepared in the 'reloc' phase and passed to the
// external linker in the 'asmb' phase.
if ldr.SymType(s) != sym.SDATA && ldr.SymType(s) != sym.SRODATA {
break
}
}
if target.IsElf() {
// Generate R_X86_64_RELATIVE relocations for best
// efficiency in the dynamic linker.
//
// As noted above, symbol addresses have not been
// assigned yet, so we can't generate the final reloc
// entry yet. We ultimately want:
//
// r_offset = s + r.Off
// r_info = R_X86_64_RELATIVE
// r_addend = targ + r.Add
//
// The dynamic linker will set *offset = base address +
// addend.
//
// AddAddrPlus is used for r_offset and r_addend to
// generate new R_ADDR relocations that will update
// these fields in the 'reloc' phase.
rela := ldr.MakeSymbolUpdater(syms.Rela)
rela.AddAddrPlus(target.Arch, s, int64(r.Off()))
if r.Siz() == 8 {
rela.AddUint64(target.Arch, elf.R_INFO(0, uint32(elf.R_X86_64_RELATIVE)))
} else {
ldr.Errorf(s, "unexpected relocation for dynamic symbol %s", ldr.SymName(targ))
}
rela.AddAddrPlus(target.Arch, targ, int64(r.Add()))
// Not mark r done here. So we still apply it statically,
// so in the file content we'll also have the right offset
// to the relocation target. So it can be examined statically
// (e.g. go version).
return true
}
if target.IsDarwin() {
// Mach-O relocations are a royal pain to lay out.
// They use a compact stateful bytecode representation.
// Here we record what are needed and encode them later.
ld.MachoAddRebase(s, int64(r.Off()))
// Not mark r done here. So we still apply it statically,
// so in the file content we'll also have the right offset
// to the relocation target. So it can be examined statically
// (e.g. go version).
return true
}
}
return false
}
func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, ri int, sectoff int64) bool {
out.Write64(uint64(sectoff))
elfsym := ld.ElfSymForReloc(ctxt, r.Xsym)
siz := r.Size
switch r.Type {
default:
return false
case objabi.R_ADDR, objabi.R_DWARFSECREF:
if siz == 4 {
out.Write64(uint64(elf.R_X86_64_32) | uint64(elfsym)<<32)
} else if siz == 8 {
out.Write64(uint64(elf.R_X86_64_64) | uint64(elfsym)<<32)
} else {
return false
}
case objabi.R_TLS_LE:
if siz == 4 {
out.Write64(uint64(elf.R_X86_64_TPOFF32) | uint64(elfsym)<<32)
} else {
return false
}
case objabi.R_TLS_IE:
if siz == 4 {
out.Write64(uint64(elf.R_X86_64_GOTTPOFF) | uint64(elfsym)<<32)
} else {
return false
}
case objabi.R_CALL:
if siz == 4 {
if ldr.SymType(r.Xsym) == sym.SDYNIMPORT {
out.Write64(uint64(elf.R_X86_64_PLT32) | uint64(elfsym)<<32)
} else {
out.Write64(uint64(elf.R_X86_64_PC32) | uint64(elfsym)<<32)
}
} else {
return false
}
case objabi.R_PCREL:
if siz == 4 {
if ldr.SymType(r.Xsym) == sym.SDYNIMPORT && ldr.SymElfType(r.Xsym) == elf.STT_FUNC {
out.Write64(uint64(elf.R_X86_64_PLT32) | uint64(elfsym)<<32)
} else {
out.Write64(uint64(elf.R_X86_64_PC32) | uint64(elfsym)<<32)
}
} else {
return false
}
case objabi.R_GOTPCREL:
if siz == 4 {
out.Write64(uint64(elf.R_X86_64_GOTPCREL) | uint64(elfsym)<<32)
} else {
return false
}
}
out.Write64(uint64(r.Xadd))
return true
}
func machoreloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, sectoff int64) bool {
var v uint32
rs := r.Xsym
rt := r.Type
if ldr.SymType(rs) == sym.SHOSTOBJ || rt == objabi.R_PCREL || rt == objabi.R_GOTPCREL || rt == objabi.R_CALL {
if ldr.SymDynid(rs) < 0 {
ldr.Errorf(s, "reloc %d (%s) to non-macho symbol %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymType(rs), ldr.SymType(rs))
return false
}
v = uint32(ldr.SymDynid(rs))
v |= 1 << 27 // external relocation
} else {
v = uint32(ldr.SymSect(rs).Extnum)
if v == 0 {
ldr.Errorf(s, "reloc %d (%s) to symbol %s in non-macho section %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymSect(rs).Name, ldr.SymType(rs), ldr.SymType(rs))
return false
}
}
switch rt {
default:
return false
case objabi.R_ADDR:
v |= ld.MACHO_X86_64_RELOC_UNSIGNED << 28
case objabi.R_CALL:
v |= 1 << 24 // pc-relative bit
v |= ld.MACHO_X86_64_RELOC_BRANCH << 28
// NOTE: Only works with 'external' relocation. Forced above.
case objabi.R_PCREL:
v |= 1 << 24 // pc-relative bit
v |= ld.MACHO_X86_64_RELOC_SIGNED << 28
case objabi.R_GOTPCREL:
v |= 1 << 24 // pc-relative bit
v |= ld.MACHO_X86_64_RELOC_GOT_LOAD << 28
}
switch r.Size {
default:
return false
case 1:
v |= 0 << 25
case 2:
v |= 1 << 25
case 4:
v |= 2 << 25
case 8:
v |= 3 << 25
}
out.Write32(uint32(sectoff))
out.Write32(v)
return true
}
func pereloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, sectoff int64) bool {
var v uint32
rs := r.Xsym
rt := r.Type
if ldr.SymDynid(rs) < 0 {
ldr.Errorf(s, "reloc %d (%s) to non-coff symbol %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymType(rs), ldr.SymType(rs))
return false
}
out.Write32(uint32(sectoff))
out.Write32(uint32(ldr.SymDynid(rs)))
switch rt {
default:
return false
case objabi.R_DWARFSECREF:
v = ld.IMAGE_REL_AMD64_SECREL
case objabi.R_ADDR:
if r.Size == 8 {
v = ld.IMAGE_REL_AMD64_ADDR64
} else {
v = ld.IMAGE_REL_AMD64_ADDR32
}
case objabi.R_CALL,
objabi.R_PCREL:
v = ld.IMAGE_REL_AMD64_REL32
}
out.Write16(uint16(v))
return true
}
func archreloc(*ld.Target, *loader.Loader, *ld.ArchSyms, loader.Reloc, loader.Sym, int64) (int64, int, bool) {
return -1, 0, false
}
func archrelocvariant(*ld.Target, *loader.Loader, loader.Reloc, sym.RelocVariant, loader.Sym, int64, []byte) int64 {
log.Fatalf("unexpected relocation variant")
return -1
}
func elfsetupplt(ctxt *ld.Link, plt, got *loader.SymbolBuilder, dynamic loader.Sym) {
if plt.Size() == 0 {
// pushq got+8(IP)
plt.AddUint8(0xff)
plt.AddUint8(0x35)
plt.AddPCRelPlus(ctxt.Arch, got.Sym(), 8)
// jmpq got+16(IP)
plt.AddUint8(0xff)
plt.AddUint8(0x25)
plt.AddPCRelPlus(ctxt.Arch, got.Sym(), 16)
// nopl 0(AX)
plt.AddUint32(ctxt.Arch, 0x00401f0f)
// assume got->size == 0 too
got.AddAddrPlus(ctxt.Arch, dynamic, 0)
got.AddUint64(ctxt.Arch, 0)
got.AddUint64(ctxt.Arch, 0)
}
}
func addpltsym(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym) {
if ldr.SymPlt(s) >= 0 {
return
}
ld.Adddynsym(ldr, target, syms, s)
if target.IsElf() {
plt := ldr.MakeSymbolUpdater(syms.PLT)
got := ldr.MakeSymbolUpdater(syms.GOTPLT)
rela := ldr.MakeSymbolUpdater(syms.RelaPLT)
if plt.Size() == 0 {
panic("plt is not set up")
}
// jmpq *got+size(IP)
plt.AddUint8(0xff)
plt.AddUint8(0x25)
plt.AddPCRelPlus(target.Arch, got.Sym(), got.Size())
// add to got: pointer to current pos in plt
got.AddAddrPlus(target.Arch, plt.Sym(), plt.Size())
// pushq $x
plt.AddUint8(0x68)
plt.AddUint32(target.Arch, uint32((got.Size()-24-8)/8))
// jmpq .plt
plt.AddUint8(0xe9)
plt.AddUint32(target.Arch, uint32(-(plt.Size() + 4)))
// rela
rela.AddAddrPlus(target.Arch, got.Sym(), got.Size()-8)
sDynid := ldr.SymDynid(s)
rela.AddUint64(target.Arch, elf.R_INFO(uint32(sDynid), uint32(elf.R_X86_64_JMP_SLOT)))
rela.AddUint64(target.Arch, 0)
ldr.SetPlt(s, int32(plt.Size()-16))
} else if target.IsDarwin() {
ld.AddGotSym(target, ldr, syms, s, 0)
sDynid := ldr.SymDynid(s)
lep := ldr.MakeSymbolUpdater(syms.LinkEditPLT)
lep.AddUint32(target.Arch, uint32(sDynid))
plt := ldr.MakeSymbolUpdater(syms.PLT)
ldr.SetPlt(s, int32(plt.Size()))
// jmpq *got+size(IP)
plt.AddUint8(0xff)
plt.AddUint8(0x25)
plt.AddPCRelPlus(target.Arch, syms.GOT, int64(ldr.SymGot(s)))
} else {
ldr.Errorf(s, "addpltsym: unsupported binary format")
}
}
func tlsIEtoLE(P []byte, off, size int) {
// Transform the PC-relative instruction into a constant load.
// That is,
//
// MOVQ X(IP), REG -> MOVQ $Y, REG
//
// To determine the instruction and register, we study the op codes.
// Consult an AMD64 instruction encoding guide to decipher this.
if off < 3 {
log.Fatal("R_X86_64_GOTTPOFF reloc not preceded by MOVQ or ADDQ instruction")
}
op := P[off-3 : off]
reg := op[2] >> 3
if op[1] == 0x8b || reg == 4 {
// MOVQ
if op[0] == 0x4c {
op[0] = 0x49
} else if size == 4 && op[0] == 0x44 {
op[0] = 0x41
}
if op[1] == 0x8b {
op[1] = 0xc7
} else {
op[1] = 0x81 // special case for SP
}
op[2] = 0xc0 | reg
} else {
// An alternate op is ADDQ. This is handled by GNU gold,
// but right now is not generated by the Go compiler:
// ADDQ X(IP), REG -> ADDQ $Y, REG
// Consider adding support for it here.
log.Fatalf("expected TLS IE op to be MOVQ, got %v", op)
}
}
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