Fix __attribute__((force_align_arg_pointer)) misalignment bug

The force_align_arg_pointer attribute was using a hardcoded 16-byte
alignment value which in combination with -mstack-alignment=32 (or
larger) would produce a misaligned stack which could result in crashes
when accessing stack buffers using aligned AVX load/store instructions.

Fix the issue by using the "stackrealign" function attribute instead
of using a hardcoded 16-byte alignment.

Patch By: Gramner

Differential Revision: https://reviews.llvm.org/D45812

llvm-svn: 330331

2 files changed, 7 insertions, 22 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index f98faeb7ee6..5e842fabbf8 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -1941,13 +1941,8 @@ void X86_32TargetCodeGenInfo::setTargetAttributes(
     return;
   if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D)) {
     if (FD->hasAttr<X86ForceAlignArgPointerAttr>()) {
-      // Get the LLVM function.
       llvm::Function *Fn = cast<llvm::Function>(GV);
-
-      // Now add the 'alignstack' attribute with a value of 16.
-      llvm::AttrBuilder B;
-      B.addStackAlignmentAttr(16);
-      Fn->addAttributes(llvm::AttributeList::FunctionIndex, B);
+      Fn->addFnAttr("stackrealign");
     }
     if (FD->hasAttr<AnyX86InterruptAttr>()) {
       llvm::Function *Fn = cast<llvm::Function>(GV);
@@ -2299,13 +2294,8 @@ public:
       return;
     if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D)) {
       if (FD->hasAttr<X86ForceAlignArgPointerAttr>()) {
-        // Get the LLVM function.
-        auto *Fn = cast<llvm::Function>(GV);
-
-        // Now add the 'alignstack' attribute with a value of 16.
-        llvm::AttrBuilder B;
-        B.addStackAlignmentAttr(16);
-        Fn->addAttributes(llvm::AttributeList::FunctionIndex, B);
+        llvm::Function *Fn = cast<llvm::Function>(GV);
+        Fn->addFnAttr("stackrealign");
       }
       if (FD->hasAttr<AnyX86InterruptAttr>()) {
         llvm::Function *Fn = cast<llvm::Function>(GV);
@@ -2431,13 +2421,8 @@ void WinX86_64TargetCodeGenInfo::setTargetAttributes(
     return;
   if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D)) {
     if (FD->hasAttr<X86ForceAlignArgPointerAttr>()) {
-      // Get the LLVM function.
-      auto *Fn = cast<llvm::Function>(GV);
-
-      // Now add the 'alignstack' attribute with a value of 16.
-      llvm::AttrBuilder B;
-      B.addStackAlignmentAttr(16);
-      Fn->addAttributes(llvm::AttributeList::FunctionIndex, B);
+      llvm::Function *Fn = cast<llvm::Function>(GV);
+      Fn->addFnAttr("stackrealign");
     }
     if (FD->hasAttr<AnyX86InterruptAttr>()) {
       llvm::Function *Fn = cast<llvm::Function>(GV);
diff --git a/clang/test/CodeGen/function-attributes.c b/clang/test/CodeGen/function-attributes.c
index e1439744010..9174b8785d9 100644
--- a/clang/test/CodeGen/function-attributes.c
+++ b/clang/test/CodeGen/function-attributes.c
@@ -71,7 +71,7 @@ void f15(void) {
 
 // PR5254
 // CHECK-LABEL: define void @f16
-// CHECK: [[ALIGN:#[0-9]+]]
+// CHECK: [[SR:#[0-9]+]]
 // CHECK: {
 void __attribute__((force_align_arg_pointer)) f16(void) {
 }
@@ -112,7 +112,7 @@ void f20(void) {
 // CHECK: attributes [[NUW]] = { nounwind optsize{{.*}} }
 // CHECK: attributes [[AI]] = { alwaysinline nounwind optsize{{.*}} }
 // CHECK: attributes [[NUW_OS_RN]] = { nounwind optsize readnone{{.*}} }
-// CHECK: attributes [[ALIGN]] = { nounwind optsize alignstack=16{{.*}} }
+// CHECK: attributes [[SR]] = { nounwind optsize{{.*}} "stackrealign"{{.*}} }
 // CHECK: attributes [[RT]] = { nounwind optsize returns_twice{{.*}} }
 // CHECK: attributes [[NR]] = { noreturn optsize }
 // CHECK: attributes [[NUW_RN]] = { nounwind optsize readnone }