[llvm] r257962 - [WebAssembly] Don't create a needless .note.GNU-stack section

[Dan Gohman via llvm-commits]

Author: djg
Date: Fri Jan 15 17:59:13 2016
New Revision: 257962

URL: http://llvm.org/viewvc/llvm-project?rev=257962&view=rev
Log:
[WebAssembly] Don't create a needless .note.GNU-stack section

WebAssembly's stack will never be executable by default, so it isn't
necessary to declare .note.GNU-stack sections to request a non-executable
stack.

Differential Revision: http://reviews.llvm.org/D15969

Added:
    llvm/trunk/test/CodeGen/WebAssembly/non-executable-stack.ll
Modified:
    llvm/trunk/include/llvm/MC/MCAsmInfoELF.h
    llvm/trunk/lib/MC/MCAsmInfoELF.cpp
    llvm/trunk/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCAsmInfo.cpp

Modified: llvm/trunk/include/llvm/MC/MCAsmInfoELF.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/MC/MCAsmInfoELF.h?rev=257962&r1=257961&r2=257962&view=diff
==============================================================================
--- llvm/trunk/include/llvm/MC/MCAsmInfoELF.h (original)
+++ llvm/trunk/include/llvm/MC/MCAsmInfoELF.h Fri Jan 15 17:59:13 2016
@@ -18,6 +18,10 @@ class MCAsmInfoELF : public MCAsmInfo {
   MCSection *getNonexecutableStackSection(MCContext &Ctx) const final;
 
 protected:
+  /// Targets which have non-executable stacks by default can set this to false
+  /// to disable the special section which requests a non-executable stack.
+  bool UsesNonexecutableStackSection;
+
   MCAsmInfoELF();
 };
 }

Modified: llvm/trunk/lib/MC/MCAsmInfoELF.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCAsmInfoELF.cpp?rev=257962&r1=257961&r2=257962&view=diff
==============================================================================
--- llvm/trunk/lib/MC/MCAsmInfoELF.cpp (original)
+++ llvm/trunk/lib/MC/MCAsmInfoELF.cpp Fri Jan 15 17:59:13 2016
@@ -21,6 +21,8 @@ using namespace llvm;
 void MCAsmInfoELF::anchor() { }
 
 MCSection *MCAsmInfoELF::getNonexecutableStackSection(MCContext &Ctx) const {
+  if (!UsesNonexecutableStackSection)
+    return nullptr;
   return Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0);
 }
 
@@ -29,4 +31,5 @@ MCAsmInfoELF::MCAsmInfoELF() {
   WeakRefDirective = "\t.weak\t";
   PrivateGlobalPrefix = ".L";
   PrivateLabelPrefix = ".L";
+  UsesNonexecutableStackSection = true;
 }

Modified: llvm/trunk/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCAsmInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCAsmInfo.cpp?rev=257962&r1=257961&r2=257962&view=diff
==============================================================================
--- llvm/trunk/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCAsmInfo.cpp (original)
+++ llvm/trunk/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCAsmInfo.cpp Fri Jan 15 17:59:13 2016
@@ -48,4 +48,7 @@ WebAssemblyMCAsmInfo::WebAssemblyMCAsmIn
   ExceptionsType = ExceptionHandling::None;
 
   // TODO: UseIntegratedAssembler?
+
+  // WebAssembly's stack is never executable.
+  UsesNonexecutableStackSection = false;
 }

Added: llvm/trunk/test/CodeGen/WebAssembly/non-executable-stack.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/WebAssembly/non-executable-stack.ll?rev=257962&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/non-executable-stack.ll (added)
+++ llvm/trunk/test/CodeGen/WebAssembly/non-executable-stack.ll Fri Jan 15 17:59:13 2016
@@ -0,0 +1,9 @@
+; RUN: llc < %s -asm-verbose=false | FileCheck %s
+
+; Test that we don't emit anything declaring a non-executable stack,
+; because wasm's stack is always non-executable.
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+; CHECK-NOT: .note.GNU-stack