When a struct ends with char a[1], the size of all earlier members of the struct is _not_ sizeof(st)-1; compilers add alignment. Problem spotted by rovv. Backport candidate.

svn:r16302

1 files changed, 4 insertions, 2 deletions

diff --git a/src/or/buffers.c b/src/or/buffers.c
index 17bd85eea..d013ce2ff 100644
--- a/src/or/buffers.c
+++ b/src/or/buffers.c
@@ -69,12 +69,14 @@ typedef struct chunk_t {
                 * more than one byte long. */
 } chunk_t;
 
+#define CHUNK_HEADER_LEN STRUCT_OFFSET(chunk_t, mem[0])
+
 /** Return the number of bytes needed to allocate a chunk to hold
  * <b>memlen</b> bytes. */
-#define CHUNK_ALLOC_SIZE(memlen) (sizeof(chunk_t) + (memlen) - 1)
+#define CHUNK_ALLOC_SIZE(memlen) (CHUNK_HEADER_LEN + (memlen))
 /** Return the number of usable bytes in a chunk allocated with
  * malloc(<b>memlen</b>). */
-#define CHUNK_SIZE_WITH_ALLOC(memlen) ((memlen) - sizeof(chunk_t) + 1)
+#define CHUNK_SIZE_WITH_ALLOC(memlen) ((memlen) - CHUNK_HEADER_LEN)
 
 /** Return the next character in <b>chunk</b> onto which data can be appended.
  * If the chunk is full, this might be off the end of chunk->mem. */