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cmd/link: R_ADDR dynamic relocs for internal PIE 

This gets -buildmode=pie -ldflags=-linkmode=internal working on
Ubuntu 16.04.

Fixes #17068

Change-Id: Ice5036199005fb528cc58279a7f057170dc6b73d
Reviewed-on: https://go-review.googlesource.com/29118
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
David Crawshaw 2016-09-13 08:24:07 -04:00
parent 6fd8c006ad
commit 5940a007c1
1 changed files with 45 additions and 2 deletions
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47
src/cmd/link/internal/amd64/asm.go
View File

@ -255,16 +255,59 @@ func adddynrel(ctxt *ld.Link, s *ld.Symbol, r *ld.Reloc) bool {
return true
}
if s.Type != obj.SDATA && s.Type != obj.SRODATA {
break
// 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 := 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 {
// 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))