buflib: Add crc field protecting buflib cookie integrity

This should catch the case of buffer misuse which results
in corrupted cookie of next allocation. The check is performed
on move_block() so it may be a bit late.

There is buflib_check_valid() provided which checks the
integrity of all cookies for given context.
On DEBUG build with --sdl-thread this check is carried out
for core_ctx on every context switch to catch problems earlier.

Change-Id: I999d4576084592394e3dbd3bdf0f32935ff5f601
Reviewed-on: http://gerrit.rockbox.org/711
Reviewed-by: Thomas Martitz <kugel@rockbox.org>

firmware/include/buflib.h

@@ -40,6 +40,7 @@ union buflib_data
     struct buflib_callbacks* ops;
     char* alloc;
     union buflib_data *handle;
+    uint32_t crc;
 };
 
 struct buflib_context
@@ -346,4 +347,9 @@ int buflib_get_num_blocks(struct buflib_context *ctx);
  */
 void buflib_print_block_at(struct buflib_context *ctx, int block_num,
                             char* buf, size_t bufsize);
+
+/**
+ * Check integrity of given buflib context
+ */
+void buflib_check_valid(struct buflib_context *ctx);
 #endif

firmware/include/core_alloc.h

@@ -17,6 +17,9 @@ bool core_shrink(int handle, void* new_start, size_t new_size);
 int core_free(int handle);
 size_t core_available(void);
 size_t core_allocatable(void);
+#ifdef DEBUG
+void core_check_valid(void);
+#endif
 
 /* DO NOT ADD wrappers for buflib_buffer_out/in. They do not call
  * the move callbacks and are therefore unsafe in the core */

firmware/include/crc32.h

@@ -18,10 +18,12 @@
  * KIND, either express or implied.
  *
  ****************************************************************************/
+#include <stdint.h>
+
 #ifndef _CRC32_H
 #define _CRC32_H
 
-unsigned crc_32(const void *src, unsigned len, unsigned crc32);
+uint32_t crc_32(const void *src, uint32_t len, uint32_t crc32);
 
 #endif