[MC] Make .note.GNU-stack explicit for the trampoline case #151754
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llvmbot added backend:AArch64 backend:RISC-V llvm:codegen llvm:mc 
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| @llvm/pr-subscribers-mc @llvm/pr-subscribers-backend-aarch64 Author: None (ssijaric-nv) ChangesIn the presence of trampolines, the .note.GNU-stack section is not emitted. The The GNU ld 2.43 on x86 machines, for example, issues the following: missing .note.GNU-stack section implies executable stack On one of the ARM machines, the absence of .note.GNU-stack results in the stack STACK off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**4 This change just emits the explicit .note.GNU-stack and marks it executable if required. Full diff: https://github.com/llvm/llvm-project/pull/151754.diff 6 Files Affected:
diff --git a/llvm/include/llvm/MC/MCAsmInfo.h b/llvm/include/llvm/MC/MCAsmInfo.h index 6c12cd347901a..1e87ce23b158b 100644 --- a/llvm/include/llvm/MC/MCAsmInfo.h +++ b/llvm/include/llvm/MC/MCAsmInfo.h @@ -471,6 +471,12 @@ class LLVM_ABI MCAsmInfo { return nullptr; } + /// Targets can implement this method to specify a section to switch to if the + /// translation has trampolines that require an executable stack. + virtual MCSection *getExecutableStackSection(MCContext &Ctx) const { + return nullptr; + } + virtual const MCExpr *getExprForPersonalitySymbol(const MCSymbol *Sym, unsigned Encoding, MCStreamer &Streamer) const; diff --git a/llvm/include/llvm/MC/MCAsmInfoELF.h b/llvm/include/llvm/MC/MCAsmInfoELF.h index c05e4ad78ecd1..c5dff900227fd 100644 --- a/llvm/include/llvm/MC/MCAsmInfoELF.h +++ b/llvm/include/llvm/MC/MCAsmInfoELF.h @@ -16,6 +16,7 @@ namespace llvm { class MCAsmInfoELF : public MCAsmInfo { virtual void anchor(); MCSection *getNonexecutableStackSection(MCContext &Ctx) const final; + MCSection *getExecutableStackSection(MCContext &Ctx) const final; void printSwitchToSection(const MCSection &, uint32_t, const Triple &, raw_ostream &) const final; bool useCodeAlign(const MCSection &Sec) const final; diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp index 1641c3eb535a9..cb697cd64d199 100644 --- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp +++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp @@ -2840,9 +2840,13 @@ bool AsmPrinter::doFinalization(Module &M) { // If we don't have any trampolines, then we don't require stack memory // to be executable. Some targets have a directive to declare this. Function *InitTrampolineIntrinsic = M.getFunction("llvm.init.trampoline"); + MCSection *S = nullptr; if (!InitTrampolineIntrinsic || InitTrampolineIntrinsic->use_empty()) - if (MCSection *S = MAI->getNonexecutableStackSection(OutContext)) - OutStreamer->switchSection(S); + S = MAI->getNonexecutableStackSection(OutContext); + else + S = MAI->getExecutableStackSection(OutContext); + if (S) + OutStreamer->switchSection(S); if (TM.Options.EmitAddrsig) { // Emit address-significance attributes for all globals. diff --git a/llvm/lib/MC/MCAsmInfoELF.cpp b/llvm/lib/MC/MCAsmInfoELF.cpp index cdae9d7860f33..495343a2c89d2 100644 --- a/llvm/lib/MC/MCAsmInfoELF.cpp +++ b/llvm/lib/MC/MCAsmInfoELF.cpp @@ -35,6 +35,14 @@ MCSection *MCAsmInfoELF::getNonexecutableStackSection(MCContext &Ctx) const { return Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0); } +MCSection *MCAsmInfoELF::getExecutableStackSection(MCContext &Ctx) const { + MCSectionELF *section = + static_cast<MCSectionELF *>(getNonexecutableStackSection(Ctx)); + if (section) + section->setFlags(section->getFlags() | ELF::SHF_EXECINSTR); + return section; +} + bool MCAsmInfoELF::useCodeAlign(const MCSection &Sec) const { return static_cast<const MCSectionELF &>(Sec).getFlags() & ELF::SHF_EXECINSTR; } diff --git a/llvm/test/CodeGen/AArch64/trampoline.ll b/llvm/test/CodeGen/AArch64/trampoline.ll index 0e682704afbf8..6689425bf5832 100644 --- a/llvm/test/CodeGen/AArch64/trampoline.ll +++ b/llvm/test/CodeGen/AArch64/trampoline.ll @@ -263,3 +263,4 @@ define i64 @func2() { %fp = call ptr @llvm.adjust.trampoline(ptr @trampg) ret i64 0 } +; CHECK-LINUX: .section ".note.GNU-stack","x",@progbits diff --git a/llvm/test/CodeGen/RISCV/rv64-trampoline.ll b/llvm/test/CodeGen/RISCV/rv64-trampoline.ll index 34d46579518ea..69c905002032d 100644 --- a/llvm/test/CodeGen/RISCV/rv64-trampoline.ll +++ b/llvm/test/CodeGen/RISCV/rv64-trampoline.ll @@ -71,6 +71,7 @@ define i64 @test0(i64 %n, ptr %p) nounwind { ; RV64-LINUX-NEXT: ld ra, 56(sp) # 8-byte Folded Reload ; RV64-LINUX-NEXT: addi sp, sp, 64 ; RV64-LINUX-NEXT: ret +; RV64-LINUX: .section ".note.GNU-stack","x",@progbits %alloca = alloca [32 x i8], align 8 call void @llvm.init.trampoline(ptr %alloca, ptr @f, ptr %p) %tramp = call ptr @llvm.adjust.trampoline(ptr %alloca) |
jrtc27 requested changes Aug 14, 2025
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To quote the top of this file:
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5 You need ; UTC_ARGS: --disable before this to mark a region that UTC should not be managing. Maybe also best to put an enable back after it.
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Thank you, @jrtc27. I'll update the test cases.
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- Same as AArch64, this is a UTC file
- This belongs outside the function
- Does non-Linux not need this too?
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Thank you, @jrtc27. I updated the test cases.
MaskRay requested changes Aug 15, 2025
llvm/include/llvm/MC/MCAsmInfo.h Outdated
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We should add a bool parameter to getNonexecutableStackSection and rename it to getStackSection.
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Thank you, @MaskRay. I renamed the getNonexecutableStackSection.
MaskRay reviewed Sep 3, 2025
llvm/tools/llvm-mc/llvm-mc.cpp Outdated
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Canonical way (preferred by clang-tidy) /*Exec=*/false. ditto above
ssijaric-nv force-pushed the trampoline_exec_stack branch from 30b44ed to 6050654 Compare ssijaric-nv force-pushed the trampoline_exec_stack branch from 6050654 to 5f5a54b Compare MaskRay approved these changes Sep 26, 2025
In the presence of trampolines, the .note.GNU-stack section is not emitted. The absence of .note.GNU-stack results in the stack marked executable by some linkers. But others require an explict .note.GNU-stack section. The GNU ld 2.43 on x86 machines, for example, issues the following: missing .note.GNU-stack section implies executable stack NOTE: This behaviour is deprecated and will be removed in a future version of the linker On one of the ARM machines, the absence of .note.GNU-stack results in the stack marked as non-executable: STACK off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**4 filesz 0x0000000000000000 memsz 0x0000000000000000 flags rw- This change just emits the explicit .note.GNU-stack and marks it executable.
ssijaric-nv force-pushed the trampoline_exec_stack branch from 5f5a54b to 1309d6a Compare 
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| LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/88/builds/16788 Here is the relevant piece of the build log for the reference |
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| This is breaking the Mac build: |
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| Thank you for letting me know, @arsenm. Is there a link to the buildbot log? I thought I removed all the traces of 'getNonexecutableStackSection'. I can revert while I investigate. |
aokblast pushed a commit to aokblast/llvm-project that referenced this pull request Oct 6, 2025
In the presence of trampolines, the .note.GNU-stack section is not emitted. The absence of .note.GNU-stack results in the stack marked executable by some linkers. But others require an explict .note.GNU-stack section. The GNU ld 2.43 on x86 machines, for example, issues the following: missing .note.GNU-stack section implies executable stack NOTE: This behaviour is deprecated and will be removed in a future version of the linker On one of the ARM machines, the absence of .note.GNU-stack results in the stack marked as non-executable: STACK off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**4 filesz 0x0000000000000000 memsz 0x0000000000000000 flags rw- This change just emits the explicit .note.GNU-stack and marks it executable if required.
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Not sure there' a bot, we have fairly poor macOS bot coverage. touching those targets MCTargetDesc seems to have worked, so maybe there's a cmake issue somewhere? |
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In the presence of trampolines, the .note.GNU-stack section is not emitted. The
absence of .note.GNU-stack results in the stack marked executable by some
linkers. But others require an explict .note.GNU-stack section.
The GNU ld 2.43 on x86 machines, for example, issues the following:
missing .note.GNU-stack section implies executable stack
NOTE: This behaviour is deprecated and will be removed in a future version of the linker
On one of the ARM machines, the absence of .note.GNU-stack results in the stack
marked as non-executable:
STACK off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**4
filesz 0x0000000000000000 memsz 0x0000000000000000 flags rw-
This change just emits the explicit .note.GNU-stack and marks it executable if required.