add support for FreeBSD's format(printf0,x,y) attribute; allows null format string.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@78276 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 46 insertions, 3 deletions

diff --git a/lib/Sema/Sema.h b/lib/Sema/Sema.h
index 0a4086fe3e..63ecdcb108 100644
--- a/lib/Sema/Sema.h
+++ b/lib/Sema/Sema.h
@@ -3308,6 +3308,7 @@ private:
   Action::OwningExprResult CheckBlockCall(NamedDecl *NDecl, CallExpr *TheCall);
   SourceLocation getLocationOfStringLiteralByte(const StringLiteral *SL,
                                                 unsigned ByteNo) const;
+  bool CheckablePrintfAttr(const FormatAttr *Format, CallExpr *TheCall);
   bool CheckObjCString(Expr *Arg);
   bool SemaBuiltinVAStart(CallExpr *TheCall);
   bool SemaBuiltinUnorderedCompare(CallExpr *TheCall);
diff --git a/lib/Sema/SemaChecking.cpp b/lib/Sema/SemaChecking.cpp
index d6095fc2ae..949c33dfff 100644
--- a/lib/Sema/SemaChecking.cpp
+++ b/lib/Sema/SemaChecking.cpp
@@ -84,6 +84,21 @@ SourceLocation Sema::getLocationOfStringLiteralByte(const StringLiteral *SL,
   }
 }
 
+/// CheckablePrintfAttr - does a function call have a "printf" attribute
+/// and arguments that merit checking?
+bool Sema::CheckablePrintfAttr(const FormatAttr *Format, CallExpr *TheCall) {
+  if (Format->getType() == "printf") return true;
+  if (Format->getType() == "printf0") {
+    // printf0 allows null "format" string; if so don't check format/args
+    unsigned format_idx = Format->getFormatIdx() - 1;
+    if (format_idx < TheCall->getNumArgs()) {
+      Expr *Format = TheCall->getArg(format_idx)->IgnoreParenCasts();
+      if (!Format->isNullPointerConstant(Context))
+        return true;
+    }
+  }
+  return false;
+}
 
 /// CheckFunctionCall - Check a direct function call for various correctness
 /// and safety properties not strictly enforced by the C type system.
@@ -167,7 +182,7 @@ Sema::CheckFunctionCall(FunctionDecl *FDecl, CallExpr *TheCall) {
 
   // Printf checking.
   if (const FormatAttr *Format = FDecl->getAttr<FormatAttr>()) {
-    if (Format->getType() == "printf") {
+    if (CheckablePrintfAttr(Format, TheCall)) {
       bool HasVAListArg = Format->getFirstArg() == 0;
       if (!HasVAListArg) {
         if (const FunctionProtoType *Proto 
@@ -201,7 +216,7 @@ Sema::CheckBlockCall(NamedDecl *NDecl, CallExpr *TheCall) {
   QualType Ty = V->getType();
   if (!Ty->isBlockPointerType())
     return move(TheCallResult);
-  if (Format->getType() == "printf") {
+  if (CheckablePrintfAttr(Format, TheCall)) {
       bool HasVAListArg = Format->getFirstArg() == 0;
       if (!HasVAListArg) {
         const FunctionType *FT = 
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 239f9951c5..3523000590 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -1212,7 +1212,8 @@ static void HandleFormatAttr(Decl *d, const AttributeList &Attr, Sema &S) {
   default: break;
   case 5: Supported = !memcmp(Format, "scanf", 5); break;
   case 6: Supported = !memcmp(Format, "printf", 6); break;
-  case 7: Supported = !memcmp(Format, "strfmon", 7); break;
+  case 7: Supported = !memcmp(Format, "printf0", 7) ||
+                      !memcmp(Format, "strfmon", 7); break;
   case 8:
     Supported = (is_strftime = !memcmp(Format, "strftime", 8)) ||
                 (is_NSString = !memcmp(Format, "NSString", 8)) ||
diff --git a/test/Sema/format-attribute-printf0.c b/test/Sema/format-attribute-printf0.c
new file mode 100644
index 0000000000..fa7eafd52f
--- /dev/null
+++ b/test/Sema/format-attribute-printf0.c
@@ -0,0 +1,26 @@
+//RUN: clang-cc -fsyntax-only -verify %s
+
+#include <stdarg.h>
+
+// same as format(printf(...))...
+void a2(const char *a, ...)    __attribute__((format(printf0, 1,2))); // no-error
+void b2(const char *a, ...)    __attribute__((format(printf0, 1,1))); // expected-error {{'format' attribute parameter 3 is out of bounds}}
+void c2(const char *a, ...)    __attribute__((format(printf0, 0,2))); // expected-error {{'format' attribute parameter 2 is out of bounds}}
+void d2(const char *a, int c)  __attribute__((format(printf0, 1,2))); // expected-error {{format attribute requires variadic function}}
+void e2(char *str, int c, ...) __attribute__((format(printf0, 2,3))); // expected-error {{format argument not a string type}}
+
+// FreeBSD usage
+#define __printf0like(fmt,va) __attribute__((__format__(__printf0__,fmt,va)))
+void null(int i, const char *a, ...) __printf0like(2,0); // no-error
+void null(int i, const char *a, ...) {
+  if (a)
+    (void)0/* vprintf(...) would go here */;
+}
+
+void callnull(void){
+  null(0,        0); // no error
+  null(0, (char*)0); // no error
+  null(0, (void*)0); // no error
+  null(0,  (int*)0); // expected-warning {{incompatible pointer types}}
+}
+