[PATCH] D46300: [Clang] Implement function attribute no_stack_protector.

[Manoj Gupta via Phabricator via cfe-commits]

manojgupta created this revision.
manojgupta added reviewers: aaron.ballman, rsmith, rnk, void.

This attribute tells clang to skip this function from stack protector
when -stack-protector option is passed.
GCC option for this is:
__attribute__((__optimize__("no-stack-protector"))) and the
equivalent clang syntax would be: __attribute__((no_stack_protector))

This is used in Linux kernel to selectively disable stack protector
in certain functions.


Repository:
  rC Clang

https://reviews.llvm.org/D46300

Files:
  include/clang/Basic/Attr.td
  lib/CodeGen/CodeGenModule.cpp
  lib/Sema/SemaDeclAttr.cpp
  test/CodeGen/stack-protector.c


Index: test/CodeGen/stack-protector.c
===================================================================
--- test/CodeGen/stack-protector.c
+++ test/CodeGen/stack-protector.c
@@ -22,6 +22,14 @@
   printf("%s\n", a);
 }
 
+// DEF: define {{.*}}void @test2(i8* %msg) #[[B:.*]] {
+__attribute__((no_stack_protector))
+void test2(const char *msg) {
+  char a[strlen(msg) + 1];
+  strcpy(a, msg);
+  printf("%s\n", a);
+}
+
 // NOSSP-NOT: attributes #[[A]] = {{.*}} ssp
 // SSP: attributes #[[A]] = {{.*}} ssp{{ }}
 // SSPSTRONG: attributes #[[A]] = {{.*}} sspstrong
@@ -33,3 +41,15 @@
 // SAFESTACK-SSP: attributes #[[A]] = {{.*}} safestack ssp{{ }}
 // SAFESTACK-SSPSTRONG: attributes #[[A]] = {{.*}} safestack sspstrong
 // SAFESTACK-SSPREQ: attributes #[[A]] = {{.*}} safestack sspreq
+
+// NOSSP-NOT: attributes #[[B]] = {{.*}} ssp
+// SSP-NOT: attributes #[[B]] = {{.*}} ssp{{ }}
+// SSPSTRONG-NOT: attributes #[[B]] = {{.*}} sspstrong
+// SSPREQ-NOT: attributes #[[B]] = {{.*}} sspreq
+
+// SAFESTACK-SSP: attributes #[[B]] = {{.*}} safestack
+// SAFESTACK-SSP-NOT: attributes #[[B]] = {{.*}} safestack ssp{{ }}
+// SAFESTACK-SSPSTRONG: attributes #[[B]] = {{.*}} safestack
+// SAFESTACK-SSPSTRONG-NOT: attributes #[[B]] = {{.*}} safestack sspstrong
+// SAFESTACK-SSPREQ: attributes #[[B]] = {{.*}} safestack
+// SAFESTACK-SSPREQ-NOT: attributes #[[B]] = {{.*}} safestack sspreq
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -6230,6 +6230,10 @@
   case AttributeList::AT_NoInstrumentFunction: // Interacts with -pg.
     handleSimpleAttribute<NoInstrumentFunctionAttr>(S, D, AL);
     break;
+  case AttributeList::AT_NoStackProtector:
+    // Interacts with -fstack-protector options.
+    handleSimpleAttribute<NoStackProtectorAttr>(S, D, AL);
+    break;
   case AttributeList::AT_StdCall:
   case AttributeList::AT_CDecl:
   case AttributeList::AT_FastCall:
Index: lib/CodeGen/CodeGenModule.cpp
===================================================================
--- lib/CodeGen/CodeGenModule.cpp
+++ lib/CodeGen/CodeGenModule.cpp
@@ -1142,12 +1142,14 @@
   if (!hasUnwindExceptions(LangOpts))
     B.addAttribute(llvm::Attribute::NoUnwind);
 
-  if (LangOpts.getStackProtector() == LangOptions::SSPOn)
-    B.addAttribute(llvm::Attribute::StackProtect);
-  else if (LangOpts.getStackProtector() == LangOptions::SSPStrong)
-    B.addAttribute(llvm::Attribute::StackProtectStrong);
-  else if (LangOpts.getStackProtector() == LangOptions::SSPReq)
-    B.addAttribute(llvm::Attribute::StackProtectReq);
+  if (!D || !D->hasAttr<NoStackProtectorAttr>()) {
+    if (LangOpts.getStackProtector() == LangOptions::SSPOn)
+      B.addAttribute(llvm::Attribute::StackProtect);
+    else if (LangOpts.getStackProtector() == LangOptions::SSPStrong)
+      B.addAttribute(llvm::Attribute::StackProtectStrong);
+    else if (LangOpts.getStackProtector() == LangOptions::SSPReq)
+      B.addAttribute(llvm::Attribute::StackProtectReq);
+  }
 
   if (!D) {
     // If we don't have a declaration to control inlining, the function isn't
Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -1490,6 +1490,12 @@
   let Documentation = [NotTailCalledDocs];
 }
 
+def NoStackProtector : InheritableAttr {
+  let Spellings = [GCC<"no_stack_protector">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [Undocumented];
+}
+
 def NoThrow : InheritableAttr {
   let Spellings = [GCC<"nothrow">, Declspec<"nothrow">];
   let Subjects = SubjectList<[Function]>;


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