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lld: Slightly simplify code and add comment.

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Cherry-pick lld r315658 by Rui Ueyama:
    This is not a mechanical transformation. Even though I believe this
    patch is correct, I'm not 100% sure if lld with this patch behaves
    exactly the same way as before on all edge cases. At least all tests
    still pass.

    I'm submitting this patch because it took almost a day to understand
    this function, and I don't want to lose it.

This fixes jemalloc assertion failures observed at startup with i386
binaries and an lld-linked libc.so.

Reviewed by:	dim
Obtained from:	LLVM r315658
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D13503
This commit is contained in:
Ed Maste 2017-12-16 14:26:11 +00:00
parent bb75e8bf8f
commit e10e2b23bf
1 changed files with 22 additions and 4 deletions
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26
contrib/llvm/tools/lld/ELF/Relocations.cpp
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@ -790,13 +790,31 @@ static void addGotEntry(SymbolBody &Sym, bool Preemptible) {
DynType = Target->GotRel;
}
bool Constant = !Preemptible && (!Config->Pic || isAbsolute(Sym));
if (!Constant)
// If a GOT slot value can be calculated at link-time, which is now,
// we can just fill that out.
//
// (We don't actually write a value to a GOT slot right now, but we
// add a static relocation to a Relocations vector so that
// InputSection::relocate will do the work for us. We may be able
// to just write a value now, but it is a TODO.)
bool IsLinkTimeConstant = !Preemptible && (!Config->Pic || isAbsolute(Sym));
if (IsLinkTimeConstant) {
InX::Got->Relocations.push_back({Expr, DynType, Off, 0, &Sym});
} else {
// Otherwise, we emit a dynamic relocation to .rel[a].dyn so that
// the GOT slot will be fixed at load-time.
In<ELFT>::RelaDyn->addReloc(
{DynType, InX::Got, Off, !Preemptible, &Sym, 0});
if (Constant || (!Config->IsRela && !Preemptible))
InX::Got->Relocations.push_back({Expr, DynType, Off, 0, &Sym});
// REL type relocations don't have addend fields unlike RELAs, and
// their addends are stored to the section to which they are applied.
// So, store addends if we need to.
//
// This is ugly -- the difference between REL and RELA should be
// handled in a better way. It's a TODO.
if (!Config->IsRela)
InX::Got->Relocations.push_back({R_ABS, Target->GotRel, Off, 0, &Sym});
}
}
// The reason we have to do this early scan is as follows