[X86] Do not end 'note.gnu.property' section with -fcf-protection

[zatrazz]

The glibc now adds the required minimum ISA level for libc-nonshared.a (linked on all programs) and this is done with an inline asm along with .note.gnu.property and .pushsection/.popsection. However, the x86 backend always ends the 'note.gnu.property' section when building with -fcf-protection, leading to assert failure:

llvm/llvm-project-git/llvm/lib/MC/MCStreamer.cpp:1251: virtual void llvm::MCStreamer::switchSection(llvm::MCSection*, const llvm::MCExpr*): Assertion `!Section->hasEnded() && "Section already ended"' failed.

[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86/isa-level.c;h=3f1b269848a52f994275bab6f60dded3ded6b144;hb=HEAD

[llvmbot]

@llvm/pr-subscribers-mc

@llvm/pr-subscribers-backend-x86

Author: Adhemerval Zanella (zatrazz)

Changes

The glibc now adds the required minimum ISA level for libc-nonshared.a (linked on all programs) and this is done with an inline asm along with .note.gnu.property and .pushsection/.popsection. However, the x86 backend always ends the 'note.gnu.property' section when building with -fcf-protection, leading to assert failure:

llvm/llvm-project-git/llvm/lib/MC/MCStreamer.cpp:1251: virtual void llvm::MCStreamer::switchSection(llvm::MCSection*, const llvm::MCExpr*): Assertion `!Section->hasEnded() && "Section already ended"' failed.

[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86/isa-level.c;h=3f1b269848a52f994275bab6f60dded3ded6b144;hb=HEAD

---

Full diff: https://github.com/llvm/llvm-project/pull/79360.diff

2 Files Affected:

• (modified) llvm/lib/Target/X86/X86AsmPrinter.cpp (-1)
• (added) llvm/test/MC/AsmParser/assembler-cf-protection-inlineasm.ll (+30)

diff --git a/llvm/lib/Target/X86/X86AsmPrinter.cpp b/llvm/lib/Target/X86/X86AsmPrinter.cpp index 9f0fd4d0938e97f..87ec8aa23080e00 100644 --- a/llvm/lib/Target/X86/X86AsmPrinter.cpp +++ b/llvm/lib/Target/X86/X86AsmPrinter.cpp @@ -877,7 +877,6 @@ void X86AsmPrinter::emitStartOfAsmFile(Module &M) { OutStreamer->emitInt32(FeatureFlagsAnd); // data emitAlignment(WordSize == 4 ? Align(4) : Align(8)); // padding - OutStreamer->endSection(Nt); OutStreamer->switchSection(Cur); } } diff --git a/llvm/test/MC/AsmParser/assembler-cf-protection-inlineasm.ll b/llvm/test/MC/AsmParser/assembler-cf-protection-inlineasm.ll new file mode 100644 index 000000000000000..a0e5b4add1b386e --- /dev/null +++ b/llvm/test/MC/AsmParser/assembler-cf-protection-inlineasm.ll @@ -0,0 +1,30 @@ +; RUN: llc -mtriple x86_64-unknown-linux-gnu %s -o %t.o -filetype=obj +; RUN: llvm-readobj -n %t.o | FileCheck %s + +module asm ".pushsection \22.note.gnu.property\22,\22a\22,@note" +module asm " .p2align 3" +module asm " .long 1f - 0f" +module asm " .long 4f - 1f" +module asm " .long 5" +module asm "0: .asciz \22GNU\22" +module asm "1: .p2align 3" +module asm " .long 0xc0008002" +module asm " .long 3f - 2f" +module asm "2: .long ((1U << 0) | 0 | 0 | 0)" +module asm "3: .p2align 3" +module asm "4:" +module asm " .popsection" + +!llvm.module.flags = !{!0, !1} + +!0 = !{i32 4, !"cf-protection-return", i32 1} +!1 = !{i32 4, !"cf-protection-branch", i32 1} + +; CHECK: Type: NT_GNU_PROPERTY_TYPE_0 +; CHECK-NEXT: Property [ +; CHECK-NEXT: x86 feature: IBT, SHSTK +; CHECK-NEXT: ] +; CHECK: Type: NT_GNU_PROPERTY_TYPE_0 +; CHECK-NEXT: Property [ +; CHECK-NEXT: x86 ISA needed: x86-64-baseline +; CHECK-NEXT: ] 

[MaskRay]

Thanks for the patch. LGTM. I think a better place for the test is llvm/test/CodeGen/X86/note-cet-property-*.ll

The problem is that codegen should not end the section, not on the MCAsmParser side.