[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.