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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190898 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86AsmPrinter.cpp b/lib/Target/X86/X86AsmPrinter.cpp
index 9e0ab82..7d7a1ad 100644
--- a/lib/Target/X86/X86AsmPrinter.cpp
+++ b/lib/Target/X86/X86AsmPrinter.cpp
@@ -518,6 +518,26 @@
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()));
+ }
+ }
}