From 2f038c4094d25597f01bfcffc3d7d9761f7aa3d4 Mon Sep 17 00:00:00 2001 From: Alexander Ivchenko Date: Mon, 4 Jun 2018 21:07:35 +0000 Subject: [X86][ELF][CET] Adding the .note.gnu.property ELF section in X86 In preparation for the proposed linker ABI changes (https://github.com/hjl-tools/linux-abi/wiki/linux-abi-draft.pdf, https://github.com/hjl-tools/x86-psABI/wiki/x86-64-psABI-cet.pdf), this patch enables emission of the .note.gnu.property section to ELF object files when building CET-enabled modules. patch by mike.dvoretsky Differential Revision: https://reviews.llvm.org/D47145 llvm-svn: 333951 --- llvm/lib/Target/X86/X86AsmPrinter.cpp | 38 +++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) (limited to 'llvm/lib/Target') diff --git a/llvm/lib/Target/X86/X86AsmPrinter.cpp b/llvm/lib/Target/X86/X86AsmPrinter.cpp index be361d5f93b..b241af43b9c 100644 --- a/llvm/lib/Target/X86/X86AsmPrinter.cpp +++ b/llvm/lib/Target/X86/X86AsmPrinter.cpp @@ -19,6 +19,7 @@ #include "X86InstrInfo.h" #include "X86MachineFunctionInfo.h" #include "llvm/BinaryFormat/COFF.h" +#include "llvm/BinaryFormat/ELF.h" #include "llvm/CodeGen/MachineConstantPool.h" #include "llvm/CodeGen/MachineModuleInfoImpls.h" #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h" @@ -30,6 +31,7 @@ #include "llvm/MC/MCContext.h" #include "llvm/MC/MCExpr.h" #include "llvm/MC/MCSectionCOFF.h" +#include "llvm/MC/MCSectionELF.h" #include "llvm/MC/MCSectionMachO.h" #include "llvm/MC/MCStreamer.h" #include "llvm/MC/MCSymbol.h" @@ -539,6 +541,42 @@ bool X86AsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI, void X86AsmPrinter::EmitStartOfAsmFile(Module &M) { const Triple &TT = TM.getTargetTriple(); + if (TT.isOSBinFormatELF()) { + // Assemble feature flags that may require creation of a note section. + unsigned FeatureFlagsAnd = 0; + if (M.getModuleFlag("cf-protection-branch")) + FeatureFlagsAnd |= ELF::GNU_PROPERTY_X86_FEATURE_1_IBT; + if (M.getModuleFlag("cf-protection-return")) + FeatureFlagsAnd |= ELF::GNU_PROPERTY_X86_FEATURE_1_SHSTK; + + if (FeatureFlagsAnd) { + // Emit a .note.gnu.property section with the flags. + if (!TT.isArch32Bit() && !TT.isArch64Bit()) + llvm_unreachable("CFProtection used on invalid architecture!"); + MCSection *Cur = OutStreamer->getCurrentSectionOnly(); + MCSection *Nt = MMI->getContext().getELFSection( + ".note.gnu.property", ELF::SHT_NOTE, ELF::SHF_ALLOC); + OutStreamer->SwitchSection(Nt); + + // Emitting note header. + int WordSize = TT.isArch64Bit() ? 8 : 4; + EmitAlignment(WordSize == 4 ? 2 : 3); + OutStreamer->EmitIntValue(4, 4 /*size*/); // data size for "GNU\0" + OutStreamer->EmitIntValue(8 + WordSize, 4 /*size*/); // Elf_Prop size + OutStreamer->EmitIntValue(ELF::NT_GNU_PROPERTY_TYPE_0, 4 /*size*/); + OutStreamer->EmitBytes(StringRef("GNU", 4)); // note name + + // Emitting an Elf_Prop for the CET properties. + OutStreamer->EmitIntValue(ELF::GNU_PROPERTY_X86_FEATURE_1_AND, 4); + OutStreamer->EmitIntValue(WordSize, 4); // data size + OutStreamer->EmitIntValue(FeatureFlagsAnd, WordSize); // data + EmitAlignment(WordSize == 4 ? 2 : 3); // padding + + OutStreamer->endSection(Nt); + OutStreamer->SwitchSection(Cur); + } + } + if (TT.isOSBinFormatMachO()) OutStreamer->SwitchSection(getObjFileLowering().getTextSection()); -- cgit v1.2.3