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)
}
// 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 {
ctxt.Diag("addpltsym: unsupported binary format")
}
}
// Append 4 bytes to s and create a R_CALL relocation targeting t to fill them in.
func addcall(ctxt *ld.Link, s *ld.Symbol, t *ld.Symbol) {
s.Attr |= ld.AttrReachable
i := s.Size
s.Size += 4
ld.Symgrow(ctxt, s, s.Size)
r := ld.Addrel(s)
r.Sym = t
r.Off = int32(i)
r.Type = obj.R_CALL
r.Siz = 4
}
func Addcall(ctxt *ld.Link, s *ld.Symbol, t *ld.Symbol) int64 {
s.Attr |= ld.AttrReachable
i := s.Size
s.Size += 4
ld.Symgrow(s, s.Size)
r := ld.Addrel(s)
r.Sym = t
r.Off = int32(i)
r.Type = obj.R_CALL
r.Siz = 4
return i + int64(r.Siz)
}
func addpltreloc(ctxt *ld.Link, plt *ld.Symbol, got *ld.Symbol, sym *ld.Symbol, typ int) *ld.Reloc {
r := ld.Addrel(plt)
r.Sym = got
r.Off = int32(plt.Size)
r.Siz = 4
r.Type = int32(typ)
r.Add = int64(sym.Got) - 8
plt.Attr |= ld.AttrReachable
plt.Size += 4
ld.Symgrow(ctxt, plt, plt.Size)
return r
}
// Convert the direct jump relocation r to refer to a trampoline if the target is too far
func trampoline(ctxt *ld.Link, r *ld.Reloc, s *ld.Symbol) {
switch r.Type {
case obj.R_CALLARM:
// r.Add is the instruction
// low 24-bit encodes the target address
t := (ld.Symaddr(r.Sym) + int64(signext24(r.Add&0xffffff)*4) - (s.Value + int64(r.Off))) / 4
if t > 0x7fffff || t < -0x800000 || (*ld.FlagDebugTramp > 1 && s.File != r.Sym.File) {
// direct call too far, need to insert trampoline
offset := (signext24(r.Add&0xffffff) + 2) * 4
var tramp *ld.Symbol
for i := 0; ; i++ {
name := r.Sym.Name + fmt.Sprintf("%+d-tramp%d", offset, i)
tramp = ctxt.Syms.Lookup(name, int(r.Sym.Version))
if tramp.Value == 0 {
// either the trampoline does not exist -- we need to create one,
// or found one the address which is not assigned -- this will be
// laid down immediately after the current function. use this one.
break
}
t = (ld.Symaddr(tramp) - 8 - (s.Value + int64(r.Off))) / 4
if t >= -0x800000 && t < 0x7fffff {
// found an existing trampoline that is not too far
// we can just use it
break
}
}
if tramp.Type == 0 {
// trampoline does not exist, create one
ctxt.AddTramp(tramp)
tramp.Size = 12 // 3 instructions
tramp.P = make([]byte, tramp.Size)
t = ld.Symaddr(r.Sym) + int64(offset)
o1 := uint32(0xe5900000 | 11<<12 | 15<<16) // MOVW (R15), R11 // R15 is actual pc + 8
o2 := uint32(0xe12fff10 | 11) // JMP (R11)
o3 := uint32(t) // WORD $target
ld.SysArch.ByteOrder.PutUint32(tramp.P, o1)
ld.SysArch.ByteOrder.PutUint32(tramp.P[4:], o2)
ld.SysArch.ByteOrder.PutUint32(tramp.P[8:], o3)
}
// modify reloc to point to tramp, which will be resolved later
r.Sym = tramp
r.Add = r.Add&0xff000000 | 0xfffffe // clear the offset embedded in the instruction
r.Done = 0
}
default:
ld.Errorf(s, "trampoline called with non-jump reloc: %v", r.Type)
}
}
// generate a trampoline to target+offset in position independent code
func gentramppic(tramp, target *ld.Symbol, offset int64) {
tramp.Size = 16 // 4 instructions
tramp.P = make([]byte, tramp.Size)
o1 := uint32(0xe5900000 | 11<<12 | 15<<16 | 4) // MOVW 4(R15), R11 // R15 is actual pc + 8
o2 := uint32(0xe0800000 | 11<<12 | 15<<16 | 11) // ADD R15, R11, R11
o3 := uint32(0xe12fff10 | 11) // JMP (R11)
o4 := uint32(0) // WORD $(target-pc) // filled in with relocation
ld.SysArch.ByteOrder.PutUint32(tramp.P, o1)
ld.SysArch.ByteOrder.PutUint32(tramp.P[4:], o2)
ld.SysArch.ByteOrder.PutUint32(tramp.P[8:], o3)
ld.SysArch.ByteOrder.PutUint32(tramp.P[12:], o4)
r := ld.Addrel(tramp)
r.Off = 12
r.Type = obj.R_PCREL
r.Siz = 4
r.Sym = target
r.Add = offset + 4
}
// generate a trampoline to target+offset
func gentramp(tramp, target *ld.Symbol, offset int64) {
tramp.Size = 12 // 3 instructions
tramp.P = make([]byte, tramp.Size)
t := ld.Symaddr(target) + int64(offset)
o1 := uint32(0xe5900000 | 11<<12 | 15<<16) // MOVW (R15), R11 // R15 is actual pc + 8
o2 := uint32(0xe12fff10 | 11) // JMP (R11)
o3 := uint32(t) // WORD $target
ld.SysArch.ByteOrder.PutUint32(tramp.P, o1)
ld.SysArch.ByteOrder.PutUint32(tramp.P[4:], o2)
ld.SysArch.ByteOrder.PutUint32(tramp.P[8:], o3)
if ld.Linkmode == ld.LinkExternal {
r := ld.Addrel(tramp)
r.Off = 8
r.Type = obj.R_ADDR
r.Siz = 4
r.Sym = target
r.Add = offset
}
}
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")
}
}
// generate a trampoline to target+offset in dynlink mode (using GOT)
func gentrampdyn(tramp, target *ld.Symbol, offset int64) {
tramp.Size = 20 // 5 instructions
o1 := uint32(0xe5900000 | 11<<12 | 15<<16 | 8) // MOVW 8(R15), R11 // R15 is actual pc + 8
o2 := uint32(0xe0800000 | 11<<12 | 15<<16 | 11) // ADD R15, R11, R11
o3 := uint32(0xe5900000 | 11<<12 | 11<<16) // MOVW (R11), R11
o4 := uint32(0xe12fff10 | 11) // JMP (R11)
o5 := uint32(0) // WORD $target@GOT // filled in with relocation
o6 := uint32(0)
if offset != 0 {
// insert an instruction to add offset
tramp.Size = 24 // 6 instructions
o6 = o5
o5 = o4
o4 = uint32(0xe2800000 | 11<<12 | 11<<16 | immrot(uint32(offset))) // ADD $offset, R11, R11
o1 = uint32(0xe5900000 | 11<<12 | 15<<16 | 12) // MOVW 12(R15), R11
}
tramp.P = make([]byte, tramp.Size)
ld.SysArch.ByteOrder.PutUint32(tramp.P, o1)
ld.SysArch.ByteOrder.PutUint32(tramp.P[4:], o2)
ld.SysArch.ByteOrder.PutUint32(tramp.P[8:], o3)
ld.SysArch.ByteOrder.PutUint32(tramp.P[12:], o4)
ld.SysArch.ByteOrder.PutUint32(tramp.P[16:], o5)
if offset != 0 {
ld.SysArch.ByteOrder.PutUint32(tramp.P[20:], o6)
}
r := ld.Addrel(tramp)
r.Off = 16
r.Type = obj.R_GOTPCREL
r.Siz = 4
r.Sym = target
r.Add = 8
if offset != 0 {
// increase reloc offset by 4 as we inserted an ADD instruction
r.Off = 20
r.Add = 12
}
}
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")
}
}
// Construct a call stub in stub that calls symbol targ via its PLT
// entry.
func gencallstub(abicase int, stub *ld.Symbol, targ *ld.Symbol) {
if abicase != 1 {
// If we see R_PPC64_TOCSAVE or R_PPC64_REL24_NOTOC
// relocations, we'll need to implement cases 2 and 3.
log.Fatalf("gencallstub only implements case 1 calls")
}
plt := ld.Linklookup(ld.Ctxt, ".plt", 0)
stub.Type = obj.STEXT
// Save TOC pointer in TOC save slot
ld.Adduint32(ld.Ctxt, stub, 0xf8410018) // std r2,24(r1)
// Load the function pointer from the PLT.
r := ld.Addrel(stub)
r.Off = int32(stub.Size)
r.Sym = plt
r.Add = int64(targ.Plt)
r.Siz = 2
if ld.Ctxt.Arch.ByteOrder == binary.BigEndian {
r.Off += int32(r.Siz)
}
r.Type = obj.R_POWER_TOC
r.Variant = ld.RV_POWER_HA
ld.Adduint32(ld.Ctxt, stub, 0x3d820000) // addis r12,r2,targ@plt@toc@ha
r = ld.Addrel(stub)
r.Off = int32(stub.Size)
r.Sym = plt
r.Add = int64(targ.Plt)
r.Siz = 2
if ld.Ctxt.Arch.ByteOrder == binary.BigEndian {
r.Off += int32(r.Siz)
}
r.Type = obj.R_POWER_TOC
r.Variant = ld.RV_POWER_LO
ld.Adduint32(ld.Ctxt, stub, 0xe98c0000) // ld r12,targ@plt@toc@l(r12)
// Jump to the loaded pointer
ld.Adduint32(ld.Ctxt, stub, 0x7d8903a6) // mtctr r12
ld.Adduint32(ld.Ctxt, stub, 0x4e800420) // bctr
}
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.Symbol) {
if s.Got >= 0 {
return
}
ld.Adddynsym(ctxt, s)
got := ld.Linklookup(ctxt, ".got", 0)
s.Got = int32(got.Size)
ld.Adduint64(ctxt, got, 0)
if ld.Iself {
rela := ld.Linklookup(ctxt, ".rela", 0)
ld.Addaddrplus(ctxt, rela, got, int64(s.Got))
ld.Adduint64(ctxt, rela, ld.ELF64_R_INFO(uint32(s.Dynid), ld.R_X86_64_GLOB_DAT))
ld.Adduint64(ctxt, rela, 0)
} else if ld.HEADTYPE == obj.Hdarwin {
ld.Adduint32(ctxt, ld.Linklookup(ctxt, ".linkedit.got", 0), uint32(s.Dynid))
} else {
ctxt.Diag("addgotsym: unsupported binary format")
}
}
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_X86_64_PC32:
if targ.Type == obj.SDYNIMPORT {
ctxt.Diag("unexpected R_X86_64_PC32 relocation for dynamic symbol %s", targ.Name)
}
if targ.Type == 0 || targ.Type == obj.SXREF {
ctxt.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(ctxt, targ)
r.Sym = ld.Linklookup(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(ctxt, targ)
r.Type = obj.R_PCREL
r.Sym = ld.Linklookup(ctxt, ".got", 0)
r.Add += 4
r.Add += int64(targ.Got)
return
case 256 + ld.R_X86_64_64:
if targ.Type == obj.SDYNIMPORT {
ctxt.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 {
ctxt.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(ctxt, targ)
r.Sym = ld.Linklookup(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 {
ctxt.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 {
ctxt.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 {
ctxt.Diag("unexpected GOT reloc for non-dynamic symbol %s", targ.Name)
}
addgotsym(ctxt, targ)
r.Type = obj.R_PCREL
r.Sym = ld.Linklookup(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(ctxt, targ)
r.Sym = ld.Linklookup(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(ctxt, targ)
r.Sym = ld.Linklookup(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(ctxt, targ)
r.Sym = ld.Linklookup(ctxt, ".got", 0)
r.Add += int64(targ.Got)
return
}
if s.Type != obj.SDATA {
break
}
if ld.Iself {
ld.Adddynsym(ctxt, targ)
rela := ld.Linklookup(ctxt, ".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 {
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
}
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 := ld.Linklookup(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(ctxt, got, 0)
ld.Adduint32(ctxt, ld.Linklookup(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
}
}
ctxt.Cursym = s
ctxt.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) 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
}
// resolve direct jump relocation r in s, and add trampoline if necessary
func trampoline(ctxt *ld.Link, r *ld.Reloc, s *ld.Symbol) {
t := ld.Symaddr(r.Sym) + r.Add - (s.Value + int64(r.Off))
switch r.Type {
case obj.R_CALLPOWER:
// If branch offset is too far then create a trampoline.
if int64(int32(t<<6)>>6) != t || (*ld.FlagDebugTramp > 1 && s.File != r.Sym.File) {
var tramp *ld.Symbol
for i := 0; ; i++ {
// Using r.Add as part of the name is significant in functions like duffzero where the call
// target is at some offset within the function. Calls to duff+8 and duff+256 must appear as
// distinct trampolines.
name := r.Sym.Name
if r.Add == 0 {
name = name + fmt.Sprintf("-tramp%d", i)
} else {
name = name + fmt.Sprintf("%+x-tramp%d", r.Add, i)
}
// Look up the trampoline in case it already exists
tramp = ctxt.Syms.Lookup(name, int(r.Sym.Version))
if tramp.Value == 0 {
break
}
t = ld.Symaddr(tramp) + r.Add - (s.Value + int64(r.Off))
// If the offset of the trampoline that has been found is within range, use it.
if int64(int32(t<<6)>>6) == t {
break
}
}
if tramp.Type == 0 {
ctxt.AddTramp(tramp)
tramp.Size = 16 // 4 instructions
tramp.P = make([]byte, tramp.Size)
t = ld.Symaddr(r.Sym) + r.Add
f := t & 0xffff0000
o1 := uint32(0x3fe00000 | (f >> 16)) // lis r31,trampaddr hi (r31 is temp reg)
f = t & 0xffff
o2 := uint32(0x63ff0000 | f) // ori r31,trampaddr lo
o3 := uint32(0x7fe903a6) // mtctr
o4 := uint32(0x4e800420) // bctr
ld.SysArch.ByteOrder.PutUint32(tramp.P, o1)
ld.SysArch.ByteOrder.PutUint32(tramp.P[4:], o2)
ld.SysArch.ByteOrder.PutUint32(tramp.P[8:], o3)
ld.SysArch.ByteOrder.PutUint32(tramp.P[12:], o4)
}
r.Sym = tramp
r.Add = 0 // This was folded into the trampoline target address
r.Done = 0
}
default:
ld.Errorf(s, "trampoline called with non-jump reloc: %v", r.Type)
}
}
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)
rela := ld.Linklookup(ctxt, ".rela.plt", 0)
if plt.Size == 0 {
elfsetupplt(ctxt)
}
// jmpq *got+size(IP)
ld.Adduint8(ctxt, plt, 0xff)
ld.Adduint8(ctxt, plt, 0x25)
ld.Addpcrelplus(ctxt, plt, got, got.Size)
// add to got: pointer to current pos in plt
ld.Addaddrplus(ctxt, got, plt, plt.Size)
// pushq $x
ld.Adduint8(ctxt, plt, 0x68)
ld.Adduint32(ctxt, plt, uint32((got.Size-24-8)/8))
// jmpq .plt
ld.Adduint8(ctxt, plt, 0xe9)
ld.Adduint32(ctxt, plt, uint32(-(plt.Size + 4)))
// rela
ld.Addaddrplus(ctxt, rela, got, got.Size-8)
ld.Adduint64(ctxt, rela, ld.ELF64_R_INFO(uint32(s.Dynid), ld.R_X86_64_JMP_SLOT))
ld.Adduint64(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(ctxt, s)
plt := ld.Linklookup(ctxt, ".plt", 0)
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.Addpcrelplus(ctxt, plt, ld.Linklookup(ctxt, ".got", 0), int64(s.Got))
} else {
ctxt.Diag("addpltsym: 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)
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(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_386_PC32:
if targ.Type == obj.SDYNIMPORT {
ctxt.Diag("unexpected R_386_PC32 relocation for dynamic symbol %s", targ.Name)
}
if targ.Type == 0 || targ.Type == obj.SXREF {
ctxt.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(ctxt, targ)
r.Sym = ld.Linklookup(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
}
ctxt.Diag("unexpected GOT reloc for non-dynamic symbol %s", targ.Name)
return
}
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_386_GOTOFF:
r.Type = obj.R_GOTOFF
return
case 256 + ld.R_386_GOTPC:
r.Type = obj.R_PCREL
r.Sym = ld.Linklookup(ctxt, ".got", 0)
r.Add += 4
return
case 256 + ld.R_386_32:
if targ.Type == obj.SDYNIMPORT {
ctxt.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 {
ctxt.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(ctxt, targ)
r.Sym = ld.Linklookup(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 {
ctxt.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(ctxt, targ)
r.Sym = ld.Linklookup(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(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_386_32))
r.Type = obj.R_CONST // write r->add during relocsym
r.Sym = nil
return
}
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 := ld.Linklookup(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(ctxt, got, 0)
ld.Adduint32(ctxt, ld.Linklookup(ctxt, ".linkedit.got", 0), uint32(targ.Dynid))
r.Type = 256 // ignore during relocsym
return
}
if ld.HEADTYPE == obj.Hwindows && s.Size == int64(ld.SysArch.PtrSize) {
// nothing to do, the relocation will be laid out in pereloc1
return
}
}
ctxt.Cursym = s
ctxt.Diag("unsupported relocation for dynamic symbol %s (type=%d stype=%d)", targ.Name, r.Type, targ.Type)
}