From c1e7621e012ddb936ee96ee3955bfb9311bff7cc Mon Sep 17 00:00:00 2001 From: Reid Kleckner Date: Tue, 17 Sep 2013 23:18:05 +0000 Subject: COFF: Ensure that objects produced by LLVM link with /safeseh 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 llvm-svn: 190898 --- llvm/lib/Target/X86/X86AsmPrinter.cpp | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'llvm/lib/Target') diff --git a/llvm/lib/Target/X86/X86AsmPrinter.cpp b/llvm/lib/Target/X86/X86AsmPrinter.cpp index 9e0ab820715..7d7a1add221 100644 --- a/llvm/lib/Target/X86/X86AsmPrinter.cpp +++ b/llvm/lib/Target/X86/X86AsmPrinter.cpp @@ -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())); + } + } } -- cgit v1.2.3