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 elfsetupplt() {
plt := ld.Linklookup(ld.Ctxt, ".plt", 0)
got := ld.Linklookup(ld.Ctxt, ".got.plt", 0)
if plt.Size == 0 {
// str lr, [sp, #-4]!
ld.Adduint32(ld.Ctxt, plt, 0xe52de004)
// ldr lr, [pc, #4]
ld.Adduint32(ld.Ctxt, plt, 0xe59fe004)
// add lr, pc, lr
ld.Adduint32(ld.Ctxt, plt, 0xe08fe00e)
// ldr pc, [lr, #8]!
ld.Adduint32(ld.Ctxt, plt, 0xe5bef008)
// .word &GLOBAL_OFFSET_TABLE[0] - .
ld.Addpcrelplus(ld.Ctxt, plt, got, 4)
// the first .plt entry requires 3 .plt.got entries
ld.Adduint32(ld.Ctxt, got, 0)
ld.Adduint32(ld.Ctxt, got, 0)
ld.Adduint32(ld.Ctxt, got, 0)
}
}
func gentext() {
if !ld.DynlinkingGo() {
return
}
addmoduledata := ld.Linklookup(ld.Ctxt, "runtime.addmoduledata", 0)
if addmoduledata.Type == ld.STEXT {
// we're linking a module containing the runtime -> no need for
// an init function
return
}
addmoduledata.Reachable = true
initfunc := ld.Linklookup(ld.Ctxt, "go.link.addmoduledata", 0)
initfunc.Type = ld.STEXT
initfunc.Local = true
initfunc.Reachable = true
o := func(op ...uint8) {
for _, op1 := range op {
ld.Adduint8(ld.Ctxt, initfunc, 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)
ld.Addpcrelplus(ld.Ctxt, initfunc, ld.Linklookup(ld.Ctxt, "runtime.firstmoduledata", 0), 0)
// 7: e8 00 00 00 00 callq c <local.dso_init+0xc>
// 8: R_X86_64_PLT32 runtime.addmoduledata-0x4
o(0xe8)
Addcall(ld.Ctxt, initfunc, addmoduledata)
// c: c3 retq
o(0xc3)
if ld.Ctxt.Etextp != nil {
ld.Ctxt.Etextp.Next = initfunc
} else {
ld.Ctxt.Textp = initfunc
}
ld.Ctxt.Etextp = initfunc
initarray_entry := ld.Linklookup(ld.Ctxt, "go.link.addmoduledatainit", 0)
initarray_entry.Reachable = true
initarray_entry.Local = true
initarray_entry.Type = ld.SINITARR
ld.Addaddr(ld.Ctxt, initarray_entry, initfunc)
}
func addpltsym(s *ld.LSym) {
if s.Plt >= 0 {
return
}
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 == ld.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")
}
}