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MC, COFF: Use relocations for function references inside the section

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Referencing one symbol from another in the same section does not
generally require a relocation.  However, the MS linker has a feature
called /INCREMENTAL which enables incremental links.  It achieves this
by creating thunks to the actual function and redirecting all
relocations to point to the thunk.

This breaks down with the old scheme if you have a function which
references, say, itself.  On x86_64, we would use %rip relative
addressing to reference the start of the function from out current
position.  This would lead to miscompiles because other references might
reference the thunk instead, breaking function pointer equality.

This fixes PR21520.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221678 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2014-11-11 08:43:57 +00:00
parent fdf59619d2
commit 16d8031f94
4 changed files with 26 additions and 5 deletions
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18
lib/MC/WinCOFFObjectWriter.cpp
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@@ -170,6 +170,11 @@ public:
void ExecutePostLayoutBinding(MCAssembler &Asm,
const MCAsmLayout &Layout) override;
bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
const MCSymbolData &DataA,
const MCFragment &FB, bool InSet,
bool IsPCRel) const override;
void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, bool &IsPCRel,
@@ -643,6 +648,19 @@ void WinCOFFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
DefineSymbol(SD, Asm, Layout);
}
bool WinCOFFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
bool InSet, bool IsPCRel) const {
// MS LINK expects to be able to replace all references to a function with a
// thunk to implement their /INCREMENTAL feature. Make sure we don't optimize
// away any relocations to functions.
if ((((DataA.getFlags() & COFF::SF_TypeMask) >> COFF::SF_TypeShift) >>
COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
return false;
return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
InSet, IsPCRel);
}
void WinCOFFObjectWriter::RecordRelocation(const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,