Add a new attribute, fortify_stdlib

This attribute applies to declarations of C stdlib functions
(sprintf, memcpy...) that have known fortified variants
(__sprintf_chk, __memcpy_chk, ...). When applied, clang will emit
calls to the fortified variant functions instead of calls to the
defaults.

In GCC, this is done by adding gnu_inline-style wrapper functions,
but that doesn't work for us for variadic functions because we don't
support __builtin_va_arg_pack (and have no intention to).

This attribute takes two arguments, the first is 'type' argument
passed through to __builtin_object_size, and the second is a flag
argument that gets passed through to the variadic checking variants.

rdar://47905754

Differential revision: https://reviews.llvm.org/D57918

llvm-svn: 353765

1 files changed, 29 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index bb69070b264..7f0ccdc6e75 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -6419,6 +6419,31 @@ static void handleObjCExternallyRetainedAttr(Sema &S, Decl *D,
   handleSimpleAttribute<ObjCExternallyRetainedAttr>(S, D, AL);
 }
 
+static void handleFortifyStdLib(Sema &S, Decl *D, const ParsedAttr &AL) {
+  auto *FD = cast<FunctionDecl>(D);
+  unsigned VariantID = Builtin::getFortifiedVariantFunction(FD->getBuiltinID());
+  if (VariantID == 0) {
+    S.Diag(D->getLocation(), diag::err_fortify_std_lib_bad_decl);
+    return;
+  }
+
+  uint32_t BOSType, Flag;
+  if (!checkUInt32Argument(S, AL, AL.getArgAsExpr(0), BOSType, 0, true) ||
+      !checkUInt32Argument(S, AL, AL.getArgAsExpr(1), Flag, 1, true))
+    return;
+
+  if (BOSType > 3) {
+    S.Diag(AL.getArgAsExpr(0)->getBeginLoc(),
+           diag::err_attribute_argument_outof_range)
+        << AL << 0 << 3;
+    return;
+  }
+
+  D->addAttr(::new (S.getASTContext()) FortifyStdLibAttr(
+      AL.getLoc(), S.getASTContext(), BOSType, Flag,
+      AL.getAttributeSpellingListIndex()));
+}
+
 //===----------------------------------------------------------------------===//
 // Top Level Sema Entry Points
 //===----------------------------------------------------------------------===//
@@ -7148,6 +7173,10 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_ObjCExternallyRetained:
     handleObjCExternallyRetainedAttr(S, D, AL);
     break;
+
+  case ParsedAttr::AT_FortifyStdLib:
+    handleFortifyStdLib(S, D, AL);
+    break;
   }
 }