mac: Suppress partial availability warnings.

util/stdlib/strnlen.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 #include "util/stdlib/strnlen.h"
 
+#if defined(OS_MACOSX) && \
+    MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_7 && \
+    MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_7
+// Forward declare a method only available on OSX 10.7+ so that

[Mark Mentovai, 2015/04/29 00:33:52]

There’s nothing really “forward” about this, it’s just your own declaration.

[erikchen, 2015/04/30 00:34:42]

Right. Updated the comment.

+// -Wpartial-availability does not emit a warning.
+size_t strnlen(const char*, size_t);

[Mark Mentovai, 2015/04/29 00:33:52]

The parameters should be named, and this ought to be in an extern "C" block.
(Did you test this?)

[erikchen, 2015/04/30 00:34:42]

I've done as you suggested. The extern "C" seems to have no effect on the final
product. (tests passes both with and without, dyldinfo shows the same symbol as
well)

+#endif
+
 namespace crashpad {
 
 #if defined(OS_MACOSX) && MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_7

[Mark Mentovai, 2015/04/29 00:33:52]

We should be sharing this #ifdef. You can move it outside of namespace crashpad.

[erikchen, 2015/04/30 00:34:42]

Done.

 size_t strnlen(const char* string, size_t max_length) {
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_7
   if (::strnlen) {

[Mark Mentovai, 2015/04/29 00:33:52]

This is a check to see whether the symbol exists at runtime, and relies on weak
import of strnlen. Does the redeclaration impact weak import?

[erikchen, 2015/04/30 00:34:42]

It does not.

$
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/dyldinfo
-bind ~/projects/chromium_official/src/out_static/Release/crashpad_handler  |
grep strnlen
__DATA  __got            0x10004C118    pointer      0 libSystem        _strnlen
(weak import)

     return ::strnlen(string, max_length);
   }
 #endif
 
   for (size_t index = 0; index < max_length; ++index) {
     if (string[index] == '\0') {
       return index;
     }
   }
 
   return max_length;
 }
 #endif
 
 }  // namespace crashpad