[MC] Make .note.GNU-stack explicit for the trampoline case #151754

ssijaric-nv · 2025-08-01T19:24:57Z

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.

llvmbot · 2025-08-14T17:20:50Z

@llvm/pr-subscribers-mc

@llvm/pr-subscribers-backend-aarch64

Author: None (ssijaric-nv)

Changes

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.

Full diff: https://github.com/llvm/llvm-project/pull/151754.diff

6 Files Affected:

(modified) llvm/include/llvm/MC/MCAsmInfo.h (+6)
(modified) llvm/include/llvm/MC/MCAsmInfoELF.h (+1)
(modified) llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp (+6-2)
(modified) llvm/lib/MC/MCAsmInfoELF.cpp (+8)
(modified) llvm/test/CodeGen/AArch64/trampoline.ll (+1)
(modified) llvm/test/CodeGen/RISCV/rv64-trampoline.ll (+1)

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 · 2025-08-14T17:38:50Z

llvm/test/CodeGen/AArch64/trampoline.ll

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.

Thank you, @jrtc27. I'll update the test cases.

jrtc27 · 2025-08-14T17:39:36Z

llvm/test/CodeGen/RISCV/rv64-trampoline.ll

Same as AArch64, this is a UTC file

This belongs outside the function

Does non-Linux not need this too?

Thank you, @jrtc27. I updated the test cases.

MaskRay · 2025-08-15T16:45:02Z

llvm/include/llvm/MC/MCAsmInfo.h

We should add a bool parameter to getNonexecutableStackSection and rename it to getStackSection.

Thank you, @MaskRay. I renamed the getNonexecutableStackSection.

MaskRay · 2025-09-03T05:16:45Z

llvm/tools/llvm-mc/llvm-mc.cpp

Canonical way (preferred by clang-tidy) /*Exec=*/false. ditto above

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.

llvm-ci · 2025-10-04T22:55:30Z

LLVM Buildbot has detected a new failure on builder openmp-s390x-linux running on systemz-1 while building llvm at step 6 "test-openmp".

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

Step 6 (test-openmp) failure: test (failure)
******************** TEST 'libomp :: tasking/issue-94260-2.c' FAILED ********************
Exit Code: -11

Command Output (stdout):
--
# RUN: at line 1
/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/./bin/clang -fopenmp   -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test -L /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src  -fno-omit-frame-pointer -mbackchain -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/ompt /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/tasking/issue-94260-2.c -o /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/tasking/Output/issue-94260-2.c.tmp -lm -latomic && /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/tasking/Output/issue-94260-2.c.tmp
# executed command: /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/./bin/clang -fopenmp -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test -L /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -fno-omit-frame-pointer -mbackchain -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/ompt /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/tasking/issue-94260-2.c -o /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/tasking/Output/issue-94260-2.c.tmp -lm -latomic
# executed command: /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/tasking/Output/issue-94260-2.c.tmp
# note: command had no output on stdout or stderr
# error: command failed with exit status: -11

--

********************

arsenm · 2025-10-06T01:40:19Z

This is breaking the Mac build:

Undefined symbols for architecture arm64:
  "llvm::MCAsmInfoELF::getNonexecutableStackSection(llvm::MCContext&) const", referenced from:
      vtable for llvm::AVRMCAsmInfo in libLLVMAVRDesc.a[6](AVRMCAsmInfo.cpp.o)
      vtable for llvm::LoongArchMCAsmInfo in libLLVMLoongArchDesc.a[7](LoongArchMCAsmInfo.cpp.o)
      vtable for llvm::SparcELFMCAsmInfo in libLLVMSparcDesc.a[5](SparcMCAsmInfo.cpp.o)
      vtable for llvm::VEELFMCAsmInfo in libLLVMVEDesc.a[5](VEMCAsmInfo.cpp.o)

ssijaric-nv · 2025-10-06T05:28:11Z

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.

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.

arsenm · 2025-10-06T11:23:43Z

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.

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?

ssijaric-nv marked this pull request as ready for review August 14, 2025 17:20

ssijaric-nv requested a review from davemgreen August 14, 2025 17:20

llvmbot added backend:AArch64 backend:RISC-V llvm:codegen llvm:mc Machine (object) code labels Aug 14, 2025

jrtc27 requested changes Aug 14, 2025

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MaskRay requested changes Aug 15, 2025

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ssijaric-nv requested review from MaskRay and jrtc27 September 2, 2025 23:33

sscalpone mentioned this pull request Sep 3, 2025

[flang] Runtime segfault with valid code #156536

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MaskRay reviewed Sep 3, 2025

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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 September 3, 2025 22:00

ssijaric-nv requested a review from MaskRay September 19, 2025 21:19

ssijaric-nv force-pushed the trampoline_exec_stack branch from 6050654 to 5f5a54b Compare September 25, 2025 20:21

MaskRay approved these changes Sep 26, 2025

View reviewed changes

ssijaric-nv added 5 commits October 4, 2025 07:59

Check for a potential null section

44b430d

Fix the test cases; use getStackSection

ab84904

Change the comments to canonical form for clang-tidy

d0d67eb

Change the BPF target to use getStackSection

1309d6a

ssijaric-nv force-pushed the trampoline_exec_stack branch from 5f5a54b to 1309d6a Compare October 4, 2025 15:57

ssijaric-nv merged commit 24c1bb6 into llvm:main Oct 4, 2025
9 checks passed

[MC] Make .note.GNU-stack explicit for the trampoline case #151754

[MC] Make .note.GNU-stack explicit for the trampoline case #151754

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