func elfsetupplt() {
plt := ld.Linklookup(ld.Ctxt, ".plt", 0)
got := ld.Linklookup(ld.Ctxt, ".got.plt", 0)
if plt.Size == 0 {
// pushl got+4
ld.Adduint8(ld.Ctxt, plt, 0xff)
ld.Adduint8(ld.Ctxt, plt, 0x35)
ld.Addaddrplus(ld.Ctxt, plt, got, 4)
// jmp *got+8
ld.Adduint8(ld.Ctxt, plt, 0xff)
ld.Adduint8(ld.Ctxt, plt, 0x25)
ld.Addaddrplus(ld.Ctxt, plt, got, 8)
// zero pad
ld.Adduint32(ld.Ctxt, plt, 0)
// assume got->size == 0 too
ld.Addaddrplus(ld.Ctxt, got, ld.Linklookup(ld.Ctxt, ".dynamic", 0), 0)
ld.Adduint32(ld.Ctxt, got, 0)
ld.Adduint32(ld.Ctxt, got, 0)
}
}
func elfsetupplt(ctxt *ld.Link) {
plt := ctxt.Syms.Lookup(".plt", 0)
got := ctxt.Syms.Lookup(".got.plt", 0)
if plt.Size == 0 {
// pushl got+4
ld.Adduint8(ctxt, plt, 0xff)
ld.Adduint8(ctxt, plt, 0x35)
ld.Addaddrplus(ctxt, plt, got, 4)
// jmp *got+8
ld.Adduint8(ctxt, plt, 0xff)
ld.Adduint8(ctxt, plt, 0x25)
ld.Addaddrplus(ctxt, plt, got, 8)
// zero pad
ld.Adduint32(ctxt, plt, 0)
// assume got->size == 0 too
ld.Addaddrplus(ctxt, got, ctxt.Syms.Lookup(".dynamic", 0), 0)
ld.Adduint32(ctxt, got, 0)
ld.Adduint32(ctxt, got, 0)
}
}
func addpltsym(ctxt *ld.Link, s *ld.LSym) {
if s.Plt >= 0 {
return
}
ld.Adddynsym(ctxt, s)
if ld.Iself {
plt := ld.Linklookup(ctxt, ".plt", 0)
got := ld.Linklookup(ctxt, ".got.plt", 0)
rel := ld.Linklookup(ctxt, ".rel.plt", 0)
if plt.Size == 0 {
elfsetupplt()
}
// jmpq *got+size
ld.Adduint8(ctxt, plt, 0xff)
ld.Adduint8(ctxt, plt, 0x25)
ld.Addaddrplus(ctxt, plt, got, got.Size)
// add to got: pointer to current pos in plt
ld.Addaddrplus(ctxt, got, plt, plt.Size)
// pushl $x
ld.Adduint8(ctxt, plt, 0x68)
ld.Adduint32(ctxt, plt, uint32(rel.Size))
// jmp .plt
ld.Adduint8(ctxt, plt, 0xe9)
ld.Adduint32(ctxt, plt, uint32(-(plt.Size + 4)))
// rel
ld.Addaddrplus(ctxt, rel, got, got.Size-4)
ld.Adduint32(ctxt, rel, ld.ELF32_R_INFO(uint32(s.Dynid), ld.R_386_JMP_SLOT))
s.Plt = int32(plt.Size - 16)
} else if ld.HEADTYPE == obj.Hdarwin {
// Same laziness as in 6l.
plt := ld.Linklookup(ctxt, ".plt", 0)
addgotsym(ctxt, s)
ld.Adduint32(ctxt, ld.Linklookup(ctxt, ".linkedit.plt", 0), uint32(s.Dynid))
// jmpq *got+size(IP)
s.Plt = int32(plt.Size)
ld.Adduint8(ctxt, plt, 0xff)
ld.Adduint8(ctxt, plt, 0x25)
ld.Addaddrplus(ctxt, plt, ld.Linklookup(ctxt, ".got", 0), int64(s.Got))
} else {
ld.Diag("addpltsym: unsupported binary format")
}
}
func elfsetupplt() {
plt := ld.Linklookup(ld.Ctxt, ".plt", 0)
got := ld.Linklookup(ld.Ctxt, ".got.plt", 0)
if plt.Size == 0 {
// pushq got+8(IP)
ld.Adduint8(ld.Ctxt, plt, 0xff)
ld.Adduint8(ld.Ctxt, plt, 0x35)
ld.Addpcrelplus(ld.Ctxt, plt, got, 8)
// jmpq got+16(IP)
ld.Adduint8(ld.Ctxt, plt, 0xff)
ld.Adduint8(ld.Ctxt, plt, 0x25)
ld.Addpcrelplus(ld.Ctxt, plt, got, 16)
// nopl 0(AX)
ld.Adduint32(ld.Ctxt, plt, 0x00401f0f)
// assume got->size == 0 too
ld.Addaddrplus(ld.Ctxt, got, ld.Linklookup(ld.Ctxt, ".dynamic", 0), 0)
ld.Adduint64(ld.Ctxt, got, 0)
ld.Adduint64(ld.Ctxt, got, 0)
}
}
func addpltsym(ctxt *ld.Link, s *ld.Symbol) {
if s.Plt >= 0 {
return
}
ld.Adddynsym(ctxt, s)
if ld.Iself {
plt := ld.Linklookup(ctxt, ".plt", 0)
got := ld.Linklookup(ctxt, ".got.plt", 0)
rel := ld.Linklookup(ctxt, ".rel.plt", 0)
if plt.Size == 0 {
elfsetupplt(ctxt)
}
// .got entry
s.Got = int32(got.Size)
// In theory, all GOT should point to the first PLT entry,
// Linux/ARM's dynamic linker will do that for us, but FreeBSD/ARM's
// dynamic linker won't, so we'd better do it ourselves.
ld.Addaddrplus(ctxt, got, plt, 0)
// .plt entry, this depends on the .got entry
s.Plt = int32(plt.Size)
addpltreloc(ctxt, plt, got, s, obj.R_PLT0) // add lr, pc, #0xXX00000
addpltreloc(ctxt, plt, got, s, obj.R_PLT1) // add lr, lr, #0xYY000
addpltreloc(ctxt, plt, got, s, obj.R_PLT2) // ldr pc, [lr, #0xZZZ]!
// rel
ld.Addaddrplus(ctxt, rel, got, int64(s.Got))
ld.Adduint32(ctxt, rel, ld.ELF32_R_INFO(uint32(s.Dynid), ld.R_ARM_JUMP_SLOT))
} else {
ctxt.Diag("addpltsym: unsupported binary format")
}
}
func elfsetupplt(ctxt *ld.Link) {
plt := ld.Linklookup(ctxt, ".plt", 0)
got := ld.Linklookup(ctxt, ".got", 0)
if plt.Size == 0 {
// stg %r1,56(%r15)
ld.Adduint8(ctxt, plt, 0xe3)
ld.Adduint8(ctxt, plt, 0x10)
ld.Adduint8(ctxt, plt, 0xf0)
ld.Adduint8(ctxt, plt, 0x38)
ld.Adduint8(ctxt, plt, 0x00)
ld.Adduint8(ctxt, plt, 0x24)
// larl %r1,_GLOBAL_OFFSET_TABLE_
ld.Adduint8(ctxt, plt, 0xc0)
ld.Adduint8(ctxt, plt, 0x10)
ld.Addpcrelplus(ctxt, plt, got, 6)
// mvc 48(8,%r15),8(%r1)
ld.Adduint8(ctxt, plt, 0xd2)
ld.Adduint8(ctxt, plt, 0x07)
ld.Adduint8(ctxt, plt, 0xf0)
ld.Adduint8(ctxt, plt, 0x30)
ld.Adduint8(ctxt, plt, 0x10)
ld.Adduint8(ctxt, plt, 0x08)
// lg %r1,16(%r1)
ld.Adduint8(ctxt, plt, 0xe3)
ld.Adduint8(ctxt, plt, 0x10)
ld.Adduint8(ctxt, plt, 0x10)
ld.Adduint8(ctxt, plt, 0x10)
ld.Adduint8(ctxt, plt, 0x00)
ld.Adduint8(ctxt, plt, 0x04)
// br %r1
ld.Adduint8(ctxt, plt, 0x07)
ld.Adduint8(ctxt, plt, 0xf1)
// nopr %r0
ld.Adduint8(ctxt, plt, 0x07)
ld.Adduint8(ctxt, plt, 0x00)
// nopr %r0
ld.Adduint8(ctxt, plt, 0x07)
ld.Adduint8(ctxt, plt, 0x00)
// nopr %r0
ld.Adduint8(ctxt, plt, 0x07)
ld.Adduint8(ctxt, plt, 0x00)
// assume got->size == 0 too
ld.Addaddrplus(ctxt, got, ld.Linklookup(ctxt, ".dynamic", 0), 0)
ld.Adduint64(ctxt, got, 0)
ld.Adduint64(ctxt, got, 0)
}
}
func addgotsyminternal(ctxt *ld.Link, s *ld.Symbol) {
if s.Got >= 0 {
return
}
got := ld.Linklookup(ctxt, ".got", 0)
s.Got = int32(got.Size)
ld.Addaddrplus(ctxt, got, s, 0)
if ld.Iself {
} else {
ctxt.Diag("addgotsyminternal: unsupported binary format")
}
}
func addgotsym(ctxt *ld.Link, s *ld.Symbol) {
if s.Got >= 0 {
return
}
ld.Adddynsym(ctxt, s)
got := ld.Linklookup(ctxt, ".got", 0)
s.Got = int32(got.Size)
ld.Adduint32(ctxt, got, 0)
if ld.Iself {
rel := ld.Linklookup(ctxt, ".rel", 0)
ld.Addaddrplus(ctxt, rel, got, int64(s.Got))
ld.Adduint32(ctxt, rel, ld.ELF32_R_INFO(uint32(s.Dynid), ld.R_ARM_GLOB_DAT))
} else {
ctxt.Diag("addgotsym: unsupported binary format")
}
}
func addpltsym(ctxt *ld.Link, s *ld.Symbol) {
if s.Plt >= 0 {
return
}
ld.Adddynsym(ctxt, s)
if ld.Iself {
plt := ld.Linklookup(ctxt, ".plt", 0)
rela := ld.Linklookup(ctxt, ".rela.plt", 0)
if plt.Size == 0 {
elfsetupplt()
}
// Create the glink resolver if necessary
glink := ensureglinkresolver()
// Write symbol resolver stub (just a branch to the
// glink resolver stub)
r := ld.Addrel(glink)
r.Sym = glink
r.Off = int32(glink.Size)
r.Siz = 4
r.Type = obj.R_CALLPOWER
ld.Adduint32(ctxt, glink, 0x48000000) // b .glink
// In the ppc64 ABI, the dynamic linker is responsible
// for writing the entire PLT. We just need to
// reserve 8 bytes for each PLT entry and generate a
// JMP_SLOT dynamic relocation for it.
//
// TODO(austin): ABI v1 is different
s.Plt = int32(plt.Size)
plt.Size += 8
ld.Addaddrplus(ctxt, rela, plt, int64(s.Plt))
ld.Adduint64(ctxt, rela, ld.ELF64_R_INFO(uint32(s.Dynid), ld.R_PPC64_JMP_SLOT))
ld.Adduint64(ctxt, rela, 0)
} else {
ld.Diag("addpltsym: unsupported binary format")
}
}
func addgotsym(s *ld.Symbol) {
if s.Got >= 0 {
return
}
ld.Adddynsym(ld.Ctxt, s)
got := ld.Linklookup(ld.Ctxt, ".got", 0)
s.Got = int32(got.Size)
ld.Adduint64(ld.Ctxt, got, 0)
if ld.Iself {
rela := ld.Linklookup(ld.Ctxt, ".rela", 0)
ld.Addaddrplus(ld.Ctxt, rela, got, int64(s.Got))
ld.Adduint64(ld.Ctxt, rela, ld.ELF64_R_INFO(uint32(s.Dynid), ld.R_390_GLOB_DAT))
ld.Adduint64(ld.Ctxt, rela, 0)
} else {
ld.Diag("addgotsym: unsupported binary format")
}
}
func addgotsym(ctxt *ld.Link, s *ld.Symbol) {
if s.Got >= 0 {
return
}
ld.Adddynsym(ctxt, s)
got := ctxt.Syms.Lookup(".got", 0)
s.Got = int32(got.Size)
ld.Adduint32(ctxt, got, 0)
if ld.Iself {
rel := ctxt.Syms.Lookup(".rel", 0)
ld.Addaddrplus(ctxt, rel, got, int64(s.Got))
ld.Adduint32(ctxt, rel, ld.ELF32_R_INFO(uint32(s.Dynid), ld.R_386_GLOB_DAT))
} else if ld.Headtype == obj.Hdarwin {
ld.Adduint32(ctxt, ctxt.Syms.Lookup(".linkedit.got", 0), uint32(s.Dynid))
} else {
ld.Errorf(s, "addgotsym: unsupported binary format")
}
}
func addgotsym(ctxt *ld.Link, s *ld.LSym) {
if s.Got >= 0 {
return
}
ld.Adddynsym(ctxt, s)
got := ld.Linklookup(ctxt, ".got", 0)
s.Got = int32(got.Size)
ld.Adduint32(ctxt, got, 0)
if ld.Iself {
rel := ld.Linklookup(ctxt, ".rel", 0)
ld.Addaddrplus(ctxt, rel, got, int64(s.Got))
ld.Adduint32(ctxt, rel, ld.ELF32_R_INFO(uint32(s.Dynid), ld.R_386_GLOB_DAT))
} else if ld.HEADTYPE == obj.Hdarwin {
ld.Adduint32(ctxt, ld.Linklookup(ctxt, ".linkedit.got", 0), uint32(s.Dynid))
} else {
ld.Diag("addgotsym: unsupported binary format")
}
}
func adddynrel(ctxt *ld.Link, s *ld.Symbol, r *ld.Reloc) bool {
targ := r.Sym
switch r.Type {
default:
if r.Type >= 256 {
ld.Errorf(s, "unexpected relocation type %d", r.Type)
return false
}
// Handle relocations found in ELF object files.
case 256 + ld.R_X86_64_PC32:
if targ.Type == obj.SDYNIMPORT {
ld.Errorf(s, "unexpected R_X86_64_PC32 relocation for dynamic symbol %s", targ.Name)
}
if targ.Type == 0 || targ.Type == obj.SXREF {
ld.Errorf(s, "unknown symbol %s in pcrel", targ.Name)
}
r.Type = obj.R_PCREL
r.Add += 4
return true
case 256 + ld.R_X86_64_PLT32:
r.Type = obj.R_PCREL
r.Add += 4
if targ.Type == obj.SDYNIMPORT {
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add += int64(targ.Plt)
}
return true
case 256 + ld.R_X86_64_GOTPCREL, 256 + ld.R_X86_64_GOTPCRELX, 256 + ld.R_X86_64_REX_GOTPCRELX:
if targ.Type != obj.SDYNIMPORT {
// have symbol
if r.Off >= 2 && s.P[r.Off-2] == 0x8b {
// turn MOVQ of GOT entry into LEAQ of symbol itself
s.P[r.Off-2] = 0x8d
r.Type = obj.R_PCREL
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
addgotsym(ctxt, targ)
r.Type = obj.R_PCREL
r.Sym = ctxt.Syms.Lookup(".got", 0)
r.Add += 4
r.Add += int64(targ.Got)
return true
case 256 + ld.R_X86_64_64:
if targ.Type == obj.SDYNIMPORT {
ld.Errorf(s, "unexpected R_X86_64_64 relocation for dynamic symbol %s", targ.Name)
}
r.Type = obj.R_ADDR
return true
// Handle relocations found in Mach-O object files.
case 512 + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 0,
512 + ld.MACHO_X86_64_RELOC_SIGNED*2 + 0,
512 + ld.MACHO_X86_64_RELOC_BRANCH*2 + 0:
// TODO: What is the difference between all these?
r.Type = obj.R_ADDR
if targ.Type == obj.SDYNIMPORT {
ld.Errorf(s, "unexpected reloc for dynamic symbol %s", targ.Name)
}
return true
case 512 + ld.MACHO_X86_64_RELOC_BRANCH*2 + 1:
if targ.Type == obj.SDYNIMPORT {
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add = int64(targ.Plt)
r.Type = obj.R_PCREL
return true
}
fallthrough
// fall through
case 512 + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 1,
512 + ld.MACHO_X86_64_RELOC_SIGNED*2 + 1,
512 + ld.MACHO_X86_64_RELOC_SIGNED_1*2 + 1,
512 + ld.MACHO_X86_64_RELOC_SIGNED_2*2 + 1,
512 + ld.MACHO_X86_64_RELOC_SIGNED_4*2 + 1:
r.Type = obj.R_PCREL
if targ.Type == obj.SDYNIMPORT {
ld.Errorf(s, "unexpected pc-relative reloc for dynamic symbol %s", targ.Name)
}
return true
case 512 + ld.MACHO_X86_64_RELOC_GOT_LOAD*2 + 1:
if targ.Type != obj.SDYNIMPORT {
// have symbol
// turn MOVQ of GOT entry into LEAQ of symbol itself
if r.Off < 2 || s.P[r.Off-2] != 0x8b {
ld.Errorf(s, "unexpected GOT_LOAD reloc for non-dynamic symbol %s", targ.Name)
return false
}
s.P[r.Off-2] = 0x8d
r.Type = obj.R_PCREL
return true
}
fallthrough
// fall through
case 512 + ld.MACHO_X86_64_RELOC_GOT*2 + 1:
if targ.Type != obj.SDYNIMPORT {
ld.Errorf(s, "unexpected GOT reloc for non-dynamic symbol %s", targ.Name)
}
addgotsym(ctxt, targ)
r.Type = obj.R_PCREL
r.Sym = ctxt.Syms.Lookup(".got", 0)
r.Add += int64(targ.Got)
return true
}
switch r.Type {
case obj.R_CALL,
obj.R_PCREL:
if targ.Type != obj.SDYNIMPORT {
// nothing to do, the relocation will be laid out in reloc
return true
}
if ld.Headtype == obj.Hwindows || ld.Headtype == obj.Hwindowsgui {
// nothing to do, the relocation will be laid out in pereloc1
return true
} else {
// for both ELF and Mach-O
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add = int64(targ.Plt)
return true
}
case obj.R_ADDR:
if s.Type == obj.STEXT && ld.Iself {
if ld.Headtype == obj.Hsolaris {
addpltsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".plt", 0)
r.Add += int64(targ.Plt)
return true
}
// The code is asking for the address of an external
// function. We provide it with the address of the
// correspondent GOT symbol.
addgotsym(ctxt, targ)
r.Sym = ctxt.Syms.Lookup(".got", 0)
r.Add += int64(targ.Got)
return true
}
// Process dynamic relocations for the data sections.
if ld.Buildmode == ld.BuildmodePIE && ld.Linkmode == ld.LinkInternal {
// 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.
switch s.Name {
case ".dynsym", ".rela", ".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 s.Type != obj.SDATA && s.Type != obj.SRODATA {
break
}
}
if ld.Iself {
// TODO: We generate a R_X86_64_64 relocation for every R_ADDR, even
// though it would be more efficient (for the dynamic linker) if we
// generated R_X86_RELATIVE instead.
ld.Adddynsym(ctxt, targ)
rela := ctxt.Syms.Lookup(".rela", 0)
ld.Addaddrplus(ctxt, rela, s, int64(r.Off))
if r.Siz == 8 {
ld.Adduint64(ctxt, rela, ld.ELF64_R_INFO(uint32(targ.Dynid), ld.R_X86_64_64))
} else {
// TODO: never happens, remove.
ld.Adduint64(ctxt, rela, ld.ELF64_R_INFO(uint32(targ.Dynid), ld.R_X86_64_32))
}
ld.Adduint64(ctxt, rela, uint64(r.Add))
r.Type = 256 // ignore during relocsym
return true
}
if ld.Headtype == obj.Hdarwin && s.Size == int64(ld.SysArch.PtrSize) && r.Off == 0 {
// Mach-O relocations are a royal pain to lay out.
// They use a compact stateful bytecode representation
// that is too much bother to deal with.
// Instead, interpret the C declaration
// void *_Cvar_stderr = &stderr;
// as making _Cvar_stderr the name of a GOT entry
// for stderr. This is separate from the usual GOT entry,
// just in case the C code assigns to the variable,
// and of course it only works for single pointers,
// but we only need to support cgo and that's all it needs.
ld.Adddynsym(ctxt, targ)
got := ctxt.Syms.Lookup(".got", 0)
s.Type = got.Type | obj.SSUB
s.Outer = got
s.Sub = got.Sub
got.Sub = s
s.Value = got.Size
ld.Adduint64(ctxt, got, 0)
ld.Adduint32(ctxt, ctxt.Syms.Lookup(".linkedit.got", 0), uint32(targ.Dynid))
r.Type = 256 // ignore during relocsym
return true
}
if ld.Headtype == obj.Hwindows || ld.Headtype == obj.Hwindowsgui {
// nothing to do, the relocation will be laid out in pereloc1
return true
}
}
return false
}
func adddynrel(s *ld.Symbol, r *ld.Reloc) {
targ := r.Sym
ld.Ctxt.Cursym = s
switch r.Type {
default:
if r.Type >= 256 {
ld.Diag("unexpected relocation type %d", r.Type)
return
}
// Handle relocations found in ELF object files.
case 256 + ld.R_PPC64_REL24:
r.Type = obj.R_CALLPOWER
// This is a local call, so the caller isn't setting
// up r12 and r2 is the same for the caller and
// callee. Hence, we need to go to the local entry
// point. (If we don't do this, the callee will try
// to use r12 to compute r2.)
r.Add += int64(r.Sym.Localentry) * 4
if targ.Type == obj.SDYNIMPORT {
// Should have been handled in elfsetupplt
ld.Diag("unexpected R_PPC64_REL24 for dyn import")
}
return
case 256 + ld.R_PPC_REL32:
r.Type = obj.R_PCREL
r.Add += 4
if targ.Type == obj.SDYNIMPORT {
ld.Diag("unexpected R_PPC_REL32 for dyn import")
}
return
case 256 + ld.R_PPC64_ADDR64:
r.Type = obj.R_ADDR
if targ.Type == obj.SDYNIMPORT {
// These happen in .toc sections
ld.Adddynsym(ld.Ctxt, targ)
rela := ld.Linklookup(ld.Ctxt, ".rela", 0)
ld.Addaddrplus(ld.Ctxt, rela, s, int64(r.Off))
ld.Adduint64(ld.Ctxt, rela, ld.ELF64_R_INFO(uint32(targ.Dynid), ld.R_PPC64_ADDR64))
ld.Adduint64(ld.Ctxt, rela, uint64(r.Add))
r.Type = 256 // ignore during relocsym
}
return
case 256 + ld.R_PPC64_TOC16:
r.Type = obj.R_POWER_TOC
r.Variant = ld.RV_POWER_LO | ld.RV_CHECK_OVERFLOW
return
case 256 + ld.R_PPC64_TOC16_LO:
r.Type = obj.R_POWER_TOC
r.Variant = ld.RV_POWER_LO
return
case 256 + ld.R_PPC64_TOC16_HA:
r.Type = obj.R_POWER_TOC
r.Variant = ld.RV_POWER_HA | ld.RV_CHECK_OVERFLOW
return
case 256 + ld.R_PPC64_TOC16_HI:
r.Type = obj.R_POWER_TOC
r.Variant = ld.RV_POWER_HI | ld.RV_CHECK_OVERFLOW
return
case 256 + ld.R_PPC64_TOC16_DS:
r.Type = obj.R_POWER_TOC
r.Variant = ld.RV_POWER_DS | ld.RV_CHECK_OVERFLOW
return
case 256 + ld.R_PPC64_TOC16_LO_DS:
r.Type = obj.R_POWER_TOC
r.Variant = ld.RV_POWER_DS
return
case 256 + ld.R_PPC64_REL16_LO:
r.Type = obj.R_PCREL
r.Variant = ld.RV_POWER_LO
r.Add += 2 // Compensate for relocation size of 2
return
case 256 + ld.R_PPC64_REL16_HI:
r.Type = obj.R_PCREL
r.Variant = ld.RV_POWER_HI | ld.RV_CHECK_OVERFLOW
r.Add += 2
return
case 256 + ld.R_PPC64_REL16_HA:
r.Type = obj.R_PCREL
r.Variant = ld.RV_POWER_HA | ld.RV_CHECK_OVERFLOW
r.Add += 2
return
}
// Handle references to ELF symbols from our own object files.
if targ.Type != obj.SDYNIMPORT {
return
}
// TODO(austin): Translate our relocations to ELF
ld.Diag("unsupported relocation for dynamic symbol %s (type=%d stype=%d)", targ.Name, r.Type, targ.Type)
}
func adddynrel(ctxt *ld.Link, s *ld.Symbol, r *ld.Reloc) {
targ := r.Sym
ctxt.Cursym = s
switch r.Type {
default:
if r.Type >= 256 {
ctxt.Diag("unexpected relocation type %d", r.Type)
return
}
// Handle relocations found in ELF object files.
case 256 + ld.R_ARM_PLT32:
r.Type = obj.R_CALLARM
if targ.Type == obj.SDYNIMPORT {
addpltsym(ctxt, targ)
r.Sym = ld.Linklookup(ctxt, ".plt", 0)
r.Add = int64(braddoff(int32(r.Add), targ.Plt/4))
}
return
case 256 + ld.R_ARM_THM_PC22: // R_ARM_THM_CALL
ld.Exitf("R_ARM_THM_CALL, are you using -marm?")
return
case 256 + ld.R_ARM_GOT32: // R_ARM_GOT_BREL
if targ.Type != obj.SDYNIMPORT {
addgotsyminternal(ctxt, targ)
} else {
addgotsym(ctxt, targ)
}
r.Type = obj.R_CONST // write r->add during relocsym
r.Sym = nil
r.Add += int64(targ.Got)
return
case 256 + ld.R_ARM_GOT_PREL: // GOT(nil) + A - nil
if targ.Type != obj.SDYNIMPORT {
addgotsyminternal(ctxt, targ)
} else {
addgotsym(ctxt, targ)
}
r.Type = obj.R_PCREL
r.Sym = ld.Linklookup(ctxt, ".got", 0)
r.Add += int64(targ.Got) + 4
return
case 256 + ld.R_ARM_GOTOFF: // R_ARM_GOTOFF32
r.Type = obj.R_GOTOFF
return
case 256 + ld.R_ARM_GOTPC: // R_ARM_BASE_PREL
r.Type = obj.R_PCREL
r.Sym = ld.Linklookup(ctxt, ".got", 0)
r.Add += 4
return
case 256 + ld.R_ARM_CALL:
r.Type = obj.R_CALLARM
if targ.Type == obj.SDYNIMPORT {
addpltsym(ctxt, targ)
r.Sym = ld.Linklookup(ctxt, ".plt", 0)
r.Add = int64(braddoff(int32(r.Add), targ.Plt/4))
}
return
case 256 + ld.R_ARM_REL32: // R_ARM_REL32
r.Type = obj.R_PCREL
r.Add += 4
return
case 256 + ld.R_ARM_ABS32:
if targ.Type == obj.SDYNIMPORT {
ctxt.Diag("unexpected R_ARM_ABS32 relocation for dynamic symbol %s", targ.Name)
}
r.Type = obj.R_ADDR
return
// we can just ignore this, because we are targeting ARM V5+ anyway
case 256 + ld.R_ARM_V4BX:
if r.Sym != nil {
// R_ARM_V4BX is ABS relocation, so this symbol is a dummy symbol, ignore it
r.Sym.Type = 0
}
r.Sym = nil
return
case 256 + ld.R_ARM_PC24,
256 + ld.R_ARM_JUMP24:
r.Type = obj.R_CALLARM
if targ.Type == obj.SDYNIMPORT {
addpltsym(ctxt, targ)
r.Sym = ld.Linklookup(ctxt, ".plt", 0)
r.Add = int64(braddoff(int32(r.Add), targ.Plt/4))
}
return
}
// Handle references to ELF symbols from our own object files.
if targ.Type != obj.SDYNIMPORT {
return
}
switch r.Type {
case obj.R_CALLARM:
addpltsym(ctxt, targ)
r.Sym = ld.Linklookup(ctxt, ".plt", 0)
r.Add = int64(targ.Plt)
return
case obj.R_ADDR:
if s.Type != obj.SDATA {
break
}
if ld.Iself {
ld.Adddynsym(ctxt, targ)
rel := ld.Linklookup(ctxt, ".rel", 0)
ld.Addaddrplus(ctxt, rel, s, int64(r.Off))
ld.Adduint32(ctxt, rel, ld.ELF32_R_INFO(uint32(targ.Dynid), ld.R_ARM_GLOB_DAT)) // we need a nil + A dynamic reloc
r.Type = obj.R_CONST // write r->add during relocsym
r.Sym = nil
return
}
}
ctxt.Cursym = s
ctxt.Diag("unsupported relocation for dynamic symbol %s (type=%d stype=%d)", targ.Name, r.Type, targ.Type)
}
func adddynrel(s *ld.LSym, r *ld.Reloc) {
targ := r.Sym
ld.Ctxt.Cursym = s
switch r.Type {
default:
if r.Type >= 256 {
ld.Diag("unexpected relocation type %d", r.Type)
return
}
// Handle relocations found in ELF object files.
case 256 + ld.R_X86_64_PC32:
if targ.Type == obj.SDYNIMPORT {
ld.Diag("unexpected R_X86_64_PC32 relocation for dynamic symbol %s", targ.Name)
}
if targ.Type == 0 || targ.Type == obj.SXREF {
ld.Diag("unknown symbol %s in pcrel", targ.Name)
}
r.Type = obj.R_PCREL
r.Add += 4
return
case 256 + ld.R_X86_64_PLT32:
r.Type = obj.R_PCREL
r.Add += 4
if targ.Type == obj.SDYNIMPORT {
addpltsym(targ)
r.Sym = ld.Linklookup(ld.Ctxt, ".plt", 0)
r.Add += int64(targ.Plt)
}
return
case 256 + ld.R_X86_64_GOTPCREL, 256 + ld.R_X86_64_GOTPCRELX, 256 + ld.R_X86_64_REX_GOTPCRELX:
if targ.Type != obj.SDYNIMPORT {
// have symbol
if r.Off >= 2 && s.P[r.Off-2] == 0x8b {
// turn MOVQ of GOT entry into LEAQ of symbol itself
s.P[r.Off-2] = 0x8d
r.Type = obj.R_PCREL
r.Add += 4
return
}
}
// fall back to using GOT and hope for the best (CMOV*)
// TODO: just needs relocation, no need to put in .dynsym
addgotsym(targ)
r.Type = obj.R_PCREL
r.Sym = ld.Linklookup(ld.Ctxt, ".got", 0)
r.Add += 4
r.Add += int64(targ.Got)
return
case 256 + ld.R_X86_64_64:
if targ.Type == obj.SDYNIMPORT {
ld.Diag("unexpected R_X86_64_64 relocation for dynamic symbol %s", targ.Name)
}
r.Type = obj.R_ADDR
return
// Handle relocations found in Mach-O object files.
case 512 + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 0,
512 + ld.MACHO_X86_64_RELOC_SIGNED*2 + 0,
512 + ld.MACHO_X86_64_RELOC_BRANCH*2 + 0:
// TODO: What is the difference between all these?
r.Type = obj.R_ADDR
if targ.Type == obj.SDYNIMPORT {
ld.Diag("unexpected reloc for dynamic symbol %s", targ.Name)
}
return
case 512 + ld.MACHO_X86_64_RELOC_BRANCH*2 + 1:
if targ.Type == obj.SDYNIMPORT {
addpltsym(targ)
r.Sym = ld.Linklookup(ld.Ctxt, ".plt", 0)
r.Add = int64(targ.Plt)
r.Type = obj.R_PCREL
return
}
fallthrough
// fall through
case 512 + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 1,
512 + ld.MACHO_X86_64_RELOC_SIGNED*2 + 1,
512 + ld.MACHO_X86_64_RELOC_SIGNED_1*2 + 1,
512 + ld.MACHO_X86_64_RELOC_SIGNED_2*2 + 1,
512 + ld.MACHO_X86_64_RELOC_SIGNED_4*2 + 1:
r.Type = obj.R_PCREL
if targ.Type == obj.SDYNIMPORT {
ld.Diag("unexpected pc-relative reloc for dynamic symbol %s", targ.Name)
}
return
case 512 + ld.MACHO_X86_64_RELOC_GOT_LOAD*2 + 1:
if targ.Type != obj.SDYNIMPORT {
// have symbol
// turn MOVQ of GOT entry into LEAQ of symbol itself
if r.Off < 2 || s.P[r.Off-2] != 0x8b {
ld.Diag("unexpected GOT_LOAD reloc for non-dynamic symbol %s", targ.Name)
return
}
s.P[r.Off-2] = 0x8d
r.Type = obj.R_PCREL
return
}
fallthrough
// fall through
case 512 + ld.MACHO_X86_64_RELOC_GOT*2 + 1:
if targ.Type != obj.SDYNIMPORT {
ld.Diag("unexpected GOT reloc for non-dynamic symbol %s", targ.Name)
}
addgotsym(targ)
r.Type = obj.R_PCREL
r.Sym = ld.Linklookup(ld.Ctxt, ".got", 0)
r.Add += int64(targ.Got)
return
}
// Handle references to ELF symbols from our own object files.
if targ.Type != obj.SDYNIMPORT {
return
}
switch r.Type {
case obj.R_CALL,
obj.R_PCREL:
if ld.HEADTYPE == obj.Hwindows {
// nothing to do, the relocation will be laid out in pereloc1
return
} else {
// for both ELF and Mach-O
addpltsym(targ)
r.Sym = ld.Linklookup(ld.Ctxt, ".plt", 0)
r.Add = int64(targ.Plt)
return
}
case obj.R_ADDR:
if s.Type == obj.STEXT && ld.Iself {
if ld.HEADTYPE == obj.Hsolaris {
addpltsym(targ)
r.Sym = ld.Linklookup(ld.Ctxt, ".plt", 0)
r.Add += int64(targ.Plt)
return
}
// The code is asking for the address of an external
// function. We provide it with the address of the
// correspondent GOT symbol.
addgotsym(targ)
r.Sym = ld.Linklookup(ld.Ctxt, ".got", 0)
r.Add += int64(targ.Got)
return
}
if s.Type != obj.SDATA {
break
}
if ld.Iself {
ld.Adddynsym(ld.Ctxt, targ)
rela := ld.Linklookup(ld.Ctxt, ".rela", 0)
ld.Addaddrplus(ld.Ctxt, rela, s, int64(r.Off))
if r.Siz == 8 {
ld.Adduint64(ld.Ctxt, rela, ld.ELF64_R_INFO(uint32(targ.Dynid), ld.R_X86_64_64))
} else {
ld.Adduint64(ld.Ctxt, rela, ld.ELF64_R_INFO(uint32(targ.Dynid), ld.R_X86_64_32))
}
ld.Adduint64(ld.Ctxt, rela, uint64(r.Add))
r.Type = 256 // ignore during relocsym
return
}
if ld.HEADTYPE == obj.Hdarwin && s.Size == int64(ld.Thearch.Ptrsize) && r.Off == 0 {
// Mach-O relocations are a royal pain to lay out.
// They use a compact stateful bytecode representation
// that is too much bother to deal with.
// Instead, interpret the C declaration
// void *_Cvar_stderr = &stderr;
// as making _Cvar_stderr the name of a GOT entry
// for stderr. This is separate from the usual GOT entry,
// just in case the C code assigns to the variable,
// and of course it only works for single pointers,
// but we only need to support cgo and that's all it needs.
ld.Adddynsym(ld.Ctxt, targ)
got := ld.Linklookup(ld.Ctxt, ".got", 0)
s.Type = got.Type | obj.SSUB
s.Outer = got
s.Sub = got.Sub
got.Sub = s
s.Value = got.Size
ld.Adduint64(ld.Ctxt, got, 0)
ld.Adduint32(ld.Ctxt, ld.Linklookup(ld.Ctxt, ".linkedit.got", 0), uint32(targ.Dynid))
r.Type = 256 // ignore during relocsym
return
}
if ld.HEADTYPE == obj.Hwindows {
// nothing to do, the relocation will be laid out in pereloc1
return
}
}
ld.Ctxt.Cursym = s
ld.Diag("unsupported relocation for dynamic symbol %s (type=%d stype=%d)", targ.Name, r.Type, targ.Type)
}
func adddynrela(rela *ld.LSym, s *ld.LSym, r *ld.Reloc) {
ld.Addaddrplus(ld.Ctxt, rela, s, int64(r.Off))
ld.Adduint64(ld.Ctxt, rela, ld.R_X86_64_RELATIVE)
ld.Addaddrplus(ld.Ctxt, rela, r.Sym, r.Add) // Addend
}
func adddynrela(rel *ld.LSym, s *ld.LSym, r *ld.Reloc) {
ld.Addaddrplus(ld.Ctxt, rel, s, int64(r.Off))
ld.Adduint32(ld.Ctxt, rel, ld.R_ARM_RELATIVE)
}
func addpltsym(ctxt *ld.Link, s *ld.Symbol) {
if s.Plt >= 0 {
return
}
ld.Adddynsym(ctxt, s)
if ld.Iself {
plt := ld.Linklookup(ctxt, ".plt", 0)
got := ld.Linklookup(ctxt, ".got", 0)
rela := ld.Linklookup(ctxt, ".rela.plt", 0)
if plt.Size == 0 {
elfsetupplt(ctxt)
}
// larl %r1,_GLOBAL_OFFSET_TABLE_+index
ld.Adduint8(ctxt, plt, 0xc0)
ld.Adduint8(ctxt, plt, 0x10)
ld.Addpcrelplus(ctxt, plt, got, got.Size+6) // need variant?
// add to got: pointer to current pos in plt
ld.Addaddrplus(ctxt, got, plt, plt.Size+8) // weird but correct
// lg %r1,0(%r1)
ld.Adduint8(ctxt, plt, 0xe3)
ld.Adduint8(ctxt, plt, 0x10)
ld.Adduint8(ctxt, plt, 0x10)
ld.Adduint8(ctxt, plt, 0x00)
ld.Adduint8(ctxt, plt, 0x00)
ld.Adduint8(ctxt, plt, 0x04)
// br %r1
ld.Adduint8(ctxt, plt, 0x07)
ld.Adduint8(ctxt, plt, 0xf1)
// basr %r1,%r0
ld.Adduint8(ctxt, plt, 0x0d)
ld.Adduint8(ctxt, plt, 0x10)
// lgf %r1,12(%r1)
ld.Adduint8(ctxt, plt, 0xe3)
ld.Adduint8(ctxt, plt, 0x10)
ld.Adduint8(ctxt, plt, 0x10)
ld.Adduint8(ctxt, plt, 0x0c)
ld.Adduint8(ctxt, plt, 0x00)
ld.Adduint8(ctxt, plt, 0x14)
// jg .plt
ld.Adduint8(ctxt, plt, 0xc0)
ld.Adduint8(ctxt, plt, 0xf4)
ld.Adduint32(ctxt, plt, uint32(-((plt.Size - 2) >> 1))) // roll-your-own relocation
//.plt index
ld.Adduint32(ctxt, plt, uint32(rela.Size)) // rela size before current entry
// rela
ld.Addaddrplus(ctxt, rela, got, got.Size-8)
ld.Adduint64(ctxt, rela, ld.ELF64_R_INFO(uint32(s.Dynid), ld.R_390_JMP_SLOT))
ld.Adduint64(ctxt, rela, 0)
s.Plt = int32(plt.Size - 32)
} else {
ctxt.Diag("addpltsym: unsupported binary format")
}
}
func adddynrel(s *ld.LSym, r *ld.Reloc) {
targ := r.Sym
ld.Ctxt.Cursym = s
switch r.Type {
default:
if r.Type >= 256 {
ld.Diag("unexpected relocation type %d", r.Type)
return
}
// Handle relocations found in ELF object files.
case 256 + ld.R_386_PC32:
if targ.Type == obj.SDYNIMPORT {
ld.Diag("unexpected R_386_PC32 relocation for dynamic symbol %s", targ.Name)
}
if targ.Type == 0 || targ.Type == obj.SXREF {
ld.Diag("unknown symbol %s in pcrel", targ.Name)
}
r.Type = obj.R_PCREL
r.Add += 4
return
case 256 + ld.R_386_PLT32:
r.Type = obj.R_PCREL
r.Add += 4
if targ.Type == obj.SDYNIMPORT {
addpltsym(ld.Ctxt, targ)
r.Sym = ld.Linklookup(ld.Ctxt, ".plt", 0)
r.Add += int64(targ.Plt)
}
return
case 256 + ld.R_386_GOT32, 256 + ld.R_386_GOT32X:
if targ.Type != obj.SDYNIMPORT {
// have symbol
if r.Off >= 2 && s.P[r.Off-2] == 0x8b {
// turn MOVL of GOT entry into LEAL of symbol address, relative to GOT.
s.P[r.Off-2] = 0x8d
r.Type = obj.R_GOTOFF
return
}
if r.Off >= 2 && s.P[r.Off-2] == 0xff && s.P[r.Off-1] == 0xb3 {
// turn PUSHL of GOT entry into PUSHL of symbol itself.
// use unnecessary SS prefix to keep instruction same length.
s.P[r.Off-2] = 0x36
s.P[r.Off-1] = 0x68
r.Type = obj.R_ADDR
return
}
ld.Diag("unexpected GOT reloc for non-dynamic symbol %s", targ.Name)
return
}
addgotsym(ld.Ctxt, targ)
r.Type = obj.R_CONST // write r->add during relocsym
r.Sym = nil
r.Add += int64(targ.Got)
return
case 256 + ld.R_386_GOTOFF:
r.Type = obj.R_GOTOFF
return
case 256 + ld.R_386_GOTPC:
r.Type = obj.R_PCREL
r.Sym = ld.Linklookup(ld.Ctxt, ".got", 0)
r.Add += 4
return
case 256 + ld.R_386_32:
if targ.Type == obj.SDYNIMPORT {
ld.Diag("unexpected R_386_32 relocation for dynamic symbol %s", targ.Name)
}
r.Type = obj.R_ADDR
return
case 512 + ld.MACHO_GENERIC_RELOC_VANILLA*2 + 0:
r.Type = obj.R_ADDR
if targ.Type == obj.SDYNIMPORT {
ld.Diag("unexpected reloc for dynamic symbol %s", targ.Name)
}
return
case 512 + ld.MACHO_GENERIC_RELOC_VANILLA*2 + 1:
if targ.Type == obj.SDYNIMPORT {
addpltsym(ld.Ctxt, targ)
r.Sym = ld.Linklookup(ld.Ctxt, ".plt", 0)
r.Add = int64(targ.Plt)
r.Type = obj.R_PCREL
return
}
r.Type = obj.R_PCREL
return
case 512 + ld.MACHO_FAKE_GOTPCREL:
if targ.Type != obj.SDYNIMPORT {
// have symbol
// turn MOVL of GOT entry into LEAL of symbol itself
if r.Off < 2 || s.P[r.Off-2] != 0x8b {
ld.Diag("unexpected GOT reloc for non-dynamic symbol %s", targ.Name)
return
}
s.P[r.Off-2] = 0x8d
r.Type = obj.R_PCREL
return
}
addgotsym(ld.Ctxt, targ)
r.Sym = ld.Linklookup(ld.Ctxt, ".got", 0)
r.Add += int64(targ.Got)
r.Type = obj.R_PCREL
return
}
// Handle references to ELF symbols from our own object files.
if targ.Type != obj.SDYNIMPORT {
return
}
switch r.Type {
case obj.R_CALL,
obj.R_PCREL:
addpltsym(ld.Ctxt, targ)
r.Sym = ld.Linklookup(ld.Ctxt, ".plt", 0)
r.Add = int64(targ.Plt)
return
case obj.R_ADDR:
if s.Type != obj.SDATA {
break
}
if ld.Iself {
ld.Adddynsym(ld.Ctxt, targ)
rel := ld.Linklookup(ld.Ctxt, ".rel", 0)
ld.Addaddrplus(ld.Ctxt, rel, s, int64(r.Off))
ld.Adduint32(ld.Ctxt, rel, ld.ELF32_R_INFO(uint32(targ.Dynid), ld.R_386_32))
r.Type = obj.R_CONST // write r->add during relocsym
r.Sym = nil
return
}
if ld.HEADTYPE == obj.Hdarwin && s.Size == PtrSize && r.Off == 0 {
// Mach-O relocations are a royal pain to lay out.
// They use a compact stateful bytecode representation
// that is too much bother to deal with.
// Instead, interpret the C declaration
// void *_Cvar_stderr = &stderr;
// as making _Cvar_stderr the name of a GOT entry
// for stderr. This is separate from the usual GOT entry,
// just in case the C code assigns to the variable,
// and of course it only works for single pointers,
// but we only need to support cgo and that's all it needs.
ld.Adddynsym(ld.Ctxt, targ)
got := ld.Linklookup(ld.Ctxt, ".got", 0)
s.Type = got.Type | obj.SSUB
s.Outer = got
s.Sub = got.Sub
got.Sub = s
s.Value = got.Size
ld.Adduint32(ld.Ctxt, got, 0)
ld.Adduint32(ld.Ctxt, ld.Linklookup(ld.Ctxt, ".linkedit.got", 0), uint32(targ.Dynid))
r.Type = 256 // ignore during relocsym
return
}
if ld.HEADTYPE == obj.Hwindows && s.Size == PtrSize {
// nothing to do, the relocation will be laid out in pereloc1
return
}
}
ld.Ctxt.Cursym = s
ld.Diag("unsupported relocation for dynamic symbol %s (type=%d stype=%d)", targ.Name, r.Type, targ.Type)
}
func addpltsym(s *ld.LSym) {
if s.Plt >= 0 {
return
}
ld.Adddynsym(ld.Ctxt, s)
if ld.Iself {
plt := ld.Linklookup(ld.Ctxt, ".plt", 0)
got := ld.Linklookup(ld.Ctxt, ".got.plt", 0)
rela := ld.Linklookup(ld.Ctxt, ".rela.plt", 0)
if plt.Size == 0 {
elfsetupplt()
}
// jmpq *got+size(IP)
ld.Adduint8(ld.Ctxt, plt, 0xff)
ld.Adduint8(ld.Ctxt, plt, 0x25)
ld.Addpcrelplus(ld.Ctxt, plt, got, got.Size)
// add to got: pointer to current pos in plt
ld.Addaddrplus(ld.Ctxt, got, plt, plt.Size)
// pushq $x
ld.Adduint8(ld.Ctxt, plt, 0x68)
ld.Adduint32(ld.Ctxt, plt, uint32((got.Size-24-8)/8))
// jmpq .plt
ld.Adduint8(ld.Ctxt, plt, 0xe9)
ld.Adduint32(ld.Ctxt, plt, uint32(-(plt.Size + 4)))
// rela
ld.Addaddrplus(ld.Ctxt, rela, got, got.Size-8)
ld.Adduint64(ld.Ctxt, rela, ld.ELF64_R_INFO(uint32(s.Dynid), ld.R_X86_64_JMP_SLOT))
ld.Adduint64(ld.Ctxt, rela, 0)
s.Plt = int32(plt.Size - 16)
} else if ld.HEADTYPE == obj.Hdarwin {
// To do lazy symbol lookup right, we're supposed
// to tell the dynamic loader which library each
// symbol comes from and format the link info
// section just so. I'm too lazy (ha!) to do that
// so for now we'll just use non-lazy pointers,
// which don't need to be told which library to use.
//
// http://networkpx.blogspot.com/2009/09/about-lcdyldinfoonly-command.html
// has details about what we're avoiding.
addgotsym(s)
plt := ld.Linklookup(ld.Ctxt, ".plt", 0)
ld.Adduint32(ld.Ctxt, ld.Linklookup(ld.Ctxt, ".linkedit.plt", 0), uint32(s.Dynid))
// jmpq *got+size(IP)
s.Plt = int32(plt.Size)
ld.Adduint8(ld.Ctxt, plt, 0xff)
ld.Adduint8(ld.Ctxt, plt, 0x25)
ld.Addpcrelplus(ld.Ctxt, plt, ld.Linklookup(ld.Ctxt, ".got", 0), int64(s.Got))
} else {
ld.Diag("addpltsym: unsupported binary format")
}
}