Address code review comments for Wstrncat-size warning (r161440).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@161527 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/DiagnosticSemaKinds.td

@@ -373,9 +373,11 @@ def note_strlcpycat_wrong_size : Note<
   
 def warn_strncat_large_size : Warning<
   "the value of the size argument in 'strncat' is too large, might lead to a " 
-  "buffer overflow">, InGroup<StrncatSize>, DefaultWarnNoWerror;
+  "buffer overflow">, InGroup<StrncatSize>;
 def warn_strncat_src_size : Warning<"size argument in 'strncat' call appears " 
-  "to be size of the source">, InGroup<StrncatSize>, DefaultWarnNoWerror;
+  "to be size of the source">, InGroup<StrncatSize>;
+def warn_strncat_wrong_size : Warning<
+  "the value of the size argument to 'strncat' is wrong">, InGroup<StrncatSize>;
 def note_strncat_wrong_size : Note<
   "change the argument to be the free space in the destination buffer minus " 
   "the terminating null byte">;

lib/Sema/SemaChecking.cpp

@@ -3101,6 +3101,19 @@ static const Expr *ignoreLiteralAdditions(const Expr *Ex, ASTContext &Ctx) {
   return Ex;
 }
 
+static bool isConstantSizeArrayWithMoreThanOneElement(QualType Ty,
+                                                      ASTContext &Context) {
+  // Only handle constant-sized or VLAs, but not flexible members.
+  if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(Ty)) {
+    // Only issue the FIXIT for arrays of size > 1.
+    if (CAT->getSize().getSExtValue() <= 1)
+      return false;
+  } else if (!Ty->isVariableArrayType()) {
+    return false;
+  }
+  return true;
+}
+
 // Warn if the user has made the 'size' argument to strlcpy or strlcat
 // be the size of the source, instead of the destination.
 void Sema::CheckStrlcpycatArguments(const CallExpr *Call,
@@ -3151,16 +3164,8 @@ void Sema::CheckStrlcpycatArguments(const CallExpr *Call,
   // pointers if we know the actual size, like if DstArg is 'array+2'
   // we could say 'sizeof(array)-2'.
   const Expr *DstArg = Call->getArg(0)->IgnoreParenImpCasts();
-  QualType DstArgTy = DstArg->getType();
-  
-  // Only handle constant-sized or VLAs, but not flexible members.
-  if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(DstArgTy)) {
-    // Only issue the FIXIT for arrays of size > 1.
-    if (CAT->getSize().getSExtValue() <= 1)
-      return;
-  } else if (!DstArgTy->isVariableArrayType()) {
+  if (!isConstantSizeArrayWithMoreThanOneElement(DstArg->getType(), Context))
     return;
-  }
 
   SmallString<128> sizeString;
   llvm::raw_svector_ostream OS(sizeString);
@@ -3242,26 +3247,23 @@ void Sema::CheckStrncatArguments(const CallExpr *CE,
                      SM.getSpellingLoc(SR.getEnd()));
   }
 
+  // Check if the destination is an array (rather than a pointer to an array).
+  QualType DstTy = DstArg->getType();
+  bool isKnownSizeArray = isConstantSizeArrayWithMoreThanOneElement(DstTy,
+                                                                    Context);
+  if (!isKnownSizeArray) {
+    if (PatternType == 1)
+      Diag(SL, diag::warn_strncat_wrong_size) << SR;
+    else
+      Diag(SL, diag::warn_strncat_src_size) << SR;
+    return;
+  }
+
   if (PatternType == 1)
     Diag(SL, diag::warn_strncat_large_size) << SR;
   else
     Diag(SL, diag::warn_strncat_src_size) << SR;
 
-  // Output a FIXIT hint if the destination is an array (rather than a
-  // pointer to an array).  This could be enhanced to handle some
-  // pointers if we know the actual size, like if DstArg is 'array+2'
-  // we could say 'sizeof(array)-2'.
-  QualType DstArgTy = DstArg->getType();
-
-  // Only handle constant-sized or VLAs, but not flexible members.
-  if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(DstArgTy)) {
-    // Only issue the FIXIT for arrays of size > 1.
-    if (CAT->getSize().getSExtValue() <= 1)
-      return;
-  } else if (!DstArgTy->isVariableArrayType()) {
-    return;
-  }
-
   SmallString<128> sizeString;
   llvm::raw_svector_ostream OS(sizeString);
   OS << "sizeof(";

test/Sema/warn-strncat-size.c

@@ -59,7 +59,7 @@ void size_1() {
   char z[1];
   char str[] = "hi";
 
-  strncat(z, str, sizeof(z)); // expected-warning{{the value of the size argument in 'strncat' is too large, might lead to a buffer overflow}}
+  strncat(z, str, sizeof(z)); // expected-warning{{the value of the size argument to 'strncat' is wrong}}
 }
 
 // Support VLAs.
@@ -69,3 +69,8 @@ void vlas(int size) {
 
   strncat(z, str, sizeof(str)); // expected-warning {{size argument in 'strncat' call appears to be size of the source}} expected-note {{change the argument to be the free space in the destination buffer minus the terminating null byte}}
 }
+
+// Non-array type gets a different error message.
+void f(char* s, char* d) {
+  strncat(d, s, sizeof(d)); // expected-warning {{the value of the size argument to 'strncat' is wrong}}
+}