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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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19
lib/MC/WinCOFFObjectWriter.cpp
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@ -148,8 +148,8 @@ public:
object_t *createCOFFEntity(StringRef Name, list_t &List);
void DefineSection(MCSectionData const &SectionData);
void DefineSymbol(MCSymbolData const &SymbolData,
MCAssembler &Assembler);
void DefineSymbol(MCSymbolData const &SymbolData, MCAssembler &Assembler,
const MCAsmLayout &Layout);
void MakeSymbolReal(COFFSymbol &S, size_t Index);
void MakeSectionReal(COFFSection &S, size_t Number);
@ -397,7 +397,8 @@ void WinCOFFObjectWriter::DefineSection(MCSectionData const &SectionData) {
/// This function takes a section data object from the assembler
/// and creates the associated COFF symbol staging object.
void WinCOFFObjectWriter::DefineSymbol(MCSymbolData const &SymbolData,
MCAssembler &Assembler) {
MCAssembler &Assembler,
const MCAsmLayout &Layout) {
MCSymbol const &Symbol = SymbolData.getSymbol();
COFFSymbol *coff_symbol = GetOrCreateCOFFSymbol(&Symbol);
SymbolMap[&Symbol] = coff_symbol;
@ -438,6 +439,12 @@ void WinCOFFObjectWriter::DefineSymbol(MCSymbolData const &SymbolData,
const MCSymbolData &ResSymData =
Assembler.getSymbolData(Symbol.AliasedSymbol());
if (Symbol.isVariable()) {
int64_t Addr;
if (Symbol.getVariableValue()->EvaluateAsAbsolute(Addr, Layout))
coff_symbol->Data.Value = Addr;
}
coff_symbol->Data.Type = (ResSymData.getFlags() & 0x0000FFFF) >> 0;
coff_symbol->Data.StorageClass = (ResSymData.getFlags() & 0x00FF0000) >> 16;
@ -449,7 +456,9 @@ void WinCOFFObjectWriter::DefineSymbol(MCSymbolData const &SymbolData,
external ? COFF::IMAGE_SYM_CLASS_EXTERNAL : COFF::IMAGE_SYM_CLASS_STATIC;
}
if (ResSymData.Fragment != NULL)
if (Symbol.isAbsolute() || Symbol.AliasedSymbol().isVariable())
coff_symbol->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
else if (ResSymData.Fragment != NULL)
coff_symbol->Section =
SectionMap[&ResSymData.Fragment->getParent()->getSection()];
@ -597,7 +606,7 @@ void WinCOFFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
for (MCAssembler::const_symbol_iterator i = Asm.symbol_begin(),
e = Asm.symbol_end();
i != e; i++)
DefineSymbol(*i, Asm);
DefineSymbol(*i, Asm, Layout);
}
void WinCOFFObjectWriter::RecordRelocation(const MCAssembler &Asm,

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()));
}
}
}

7
test/CodeGen/X86/coff-feat00.ll Normal file
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@ -0,0 +1,7 @@
; RUN: llc -O0 -mtriple=i386-pc-win32 -filetype=asm -o - %s | FileCheck %s
define i32 @foo() {
ret i32 0
}
; CHECK: @feat.00 = 1

13
test/MC/COFF/feat00.s Normal file
View File

@ -0,0 +1,13 @@
// RUN: llvm-mc -filetype=obj -triple i686-pc-win32 %s -o - | llvm-readobj -t | FileCheck %s
"@feat.00" = 123
// CHECK: Symbol {
// CHECK: Name: @feat.00
// CHECK: Value: 123
// CHECK: Section: (-1)
// CHECK: BaseType: Null (0x0)
// CHECK: ComplexType: Null (0x0)
// CHECK: StorageClass: External (0x2)
// CHECK: AuxSymbolCount: 0
// CHECK: }