maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

Add comments on a mysterious value in MIPS GOT[1]. 

Thanks to Simon Atanasyan and Igor Kudrin for describing the code!

llvm-svn: 259259
This commit is contained in:
Rui Ueyama 2016-01-29 22:55:38 +00:00
parent 00dab22853
commit 8364c6269a
1 changed files with 17 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
lld/ELF/Target.cpp
View File

@ -1408,9 +1408,24 @@ unsigned MipsTargetInfo<ELFT>::getDynRel(unsigned Type) const {
template <class ELFT>
void MipsTargetInfo<ELFT>::writeGotHeader(uint8_t *Buf) const {
typedef typename ELFFile<ELFT>::Elf_Off Elf_Off;
typedef typename ELFFile<ELFT>::uintX_t uintX_t;
// Set the MSB of the second GOT slot. This is not required by any
// MIPS ABI documentation, though.
//
// There is a comment in glibc saying that "The MSB of got[1] of a
// gnu object is set to identify gnu objects," and in GNU gold it
// says "the second entry will be used by some runtime loaders".
// But how this field is being used is unclear.
//
// We are not really willing to mimic other linkers behaviors
// without understanding why they do that, but because all files
// generated by GNU tools have this special GOT value, and because
// we've been doing this for years, it is probably a safe bet to
// keep doing this for now. We really need to revisit this to see
// if we had to do this.
auto *P = reinterpret_cast<Elf_Off *>(Buf);
// Module pointer
P[1] = ELFT::Is64Bits ? 0x8000000000000000 : 0x80000000;
P[1] = uintX_t(1) << (ELFT::Is64Bits ? 63 : 31);
}
template <class ELFT>