C bindings: Fix signed comparsion.

mojo/public/c/bindings/lib/type_descriptor.c

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/public/c/bindings/lib/type_descriptor.h"
 
 #include <assert.h>
+#include <stddef.h>
 
 #include "mojo/public/c/bindings/array.h"
 #include "mojo/public/c/bindings/interface.h"
 #include "mojo/public/c/bindings/lib/util.h"
 #include "mojo/public/c/bindings/map.h"
 #include "mojo/public/c/bindings/struct.h"
 #include "mojo/public/c/bindings/union.h"
 
 const struct MojomTypeDescriptorArray g_mojom_string_type_description = {
     MOJOM_TYPE_DESCRIPTOR_TYPE_POD,  // elem_type
@@ skipping 60 matching lines @@
       break;
   }
   return size;
 }
 
 static void encode_pointer(union MojomPointer* pointer, uint32_t max_offset) {
   if (pointer->ptr == NULL) {
     pointer->offset = 0;
   } else {
     assert((char*)pointer->ptr > (char*)pointer);
-    assert((char*)pointer->ptr - (char*)pointer < max_offset);
+    assert((char*)pointer->ptr - (char*)pointer < (ptrdiff_t)max_offset);

[viettrungluu, 2016/08/02 20:10:29]

Hmmm. So if ptrdiff_t is 32-bit, and max_offset is big, you might have a
problem.

But since you already asserted the pointer->ptr > pointer on the previous line,
you know that the LHS is positive.

So maybe cast all of the LHS to a size_t instead?

[vardhan, 2016/08/02 20:28:30]

Done.

     pointer->offset = (char*)(pointer->ptr) - (char*)pointer;
   }
 }
 
 static void decode_pointer(union MojomPointer* pointer) {
   if (pointer->offset == 0) {
     pointer->ptr = NULL;
   } else {
     pointer->ptr = (char*)pointer + pointer->offset;
   }
@@ skipping 293 matching lines @@
       return validate_handle(*(const MojoHandle*)in_buf, in_num_handles,
                              in_nullable, inout_context);
     case MOJOM_TYPE_DESCRIPTOR_TYPE_INTERFACE:
       return validate_handle(((const struct MojomInterfaceData*)in_buf)->handle,
                              in_num_handles, in_nullable, inout_context);
     case MOJOM_TYPE_DESCRIPTOR_TYPE_POD:
       break;
   }
   return MOJOM_VALIDATION_ERROR_NONE;
 }