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COFF: Ensure that objects produced by LLVM link with /safeseh

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Summary:
We indicate that the object files are safe by emitting a @feat.00
absolute address symbol.  The address is presumably interpreted as a
bitfield of features that the compiler would like to enable.  Bit 0 is
documented in the PE COFF spec to opt in to "registered SEH", which is
what /safeseh enables.

LLVM's object files are safe by default because LLVM doesn't know how to
produce SEH handlers.

Reviewers: Bigcheese

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1691

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190898 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Kleckner
2013-09-17 23:18:05 +00:00
parent c61c811621
commit 28860823ad
4 changed files with 54 additions and 5 deletions
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20
lib/Target/X86/X86AsmPrinter.cpp
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@@ -518,6 +518,26 @@ bool X86AsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
void X86AsmPrinter::EmitStartOfAsmFile(Module &M) {
if (Subtarget->isTargetEnvMacho())
OutStreamer.SwitchSection(getObjFileLowering().getTextSection());
if (Subtarget->isTargetCOFF()) {
// Emit an absolute @feat.00 symbol. This appears to be some kind of
// compiler features bitfield read by link.exe.
if (!Subtarget->is64Bit()) {
MCSymbol *S = MMI->getContext().GetOrCreateSymbol(StringRef("@feat.00"));
OutStreamer.BeginCOFFSymbolDef(S);
OutStreamer.EmitCOFFSymbolStorageClass(COFF::IMAGE_SYM_CLASS_STATIC);
OutStreamer.EmitCOFFSymbolType(COFF::IMAGE_SYM_DTYPE_NULL);
OutStreamer.EndCOFFSymbolDef();
// According to the PE-COFF spec, the LSB of this value marks the object
// for "registered SEH". This means that all SEH handler entry points
// must be registered in .sxdata. Use of any unregistered handlers will
// cause the process to terminate immediately. LLVM does not know how to
// register any SEH handlers, so its object files should be safe.
S->setAbsolute();
OutStreamer.EmitAssignment(
S, MCConstantExpr::Create(int64_t(1), MMI->getContext()));
}
}
}