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

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;

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;

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.

llvm/lib/MC/MCAsmInfoELF.cpp

@@ -35,6 +35,13 @@ 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));
+  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;
 }

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

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)