Current libiberty md5 code triggers these warnings with gcc-4.7.1 for me: libiberty/md5.c: In function ‘md5_finish_ctx’: libiberty/md5.c:117:3: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] libiberty/md5.c:118:3: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
The change below fixes things for me. The optimized output (-O2) is the same
before/after my change on x86_64-linux. I imagine it'll be the same for most
targets. It seems simpler than using a union on the md5_ctx buffer since these
are the only two locations in the code where this occurs.
2012-07-27 Mike Frysinger <vap...@gentoo.org>
* md5.c (md5_finish_ctx): Declare swap_bytes. Assign SWAP() output
to swap_bytes, and then call memcpy to move it to ctx->buffer.
--- a/libiberty/md5.c
+++ b/libiberty/md5.c
@@ -102,7 +102,7 @@
md5_finish_ctx (struct md5_ctx *ctx, void *resbuf)
{
/* Take yet unprocessed bytes into account. */
- md5_uint32 bytes = ctx->buflen;
+ md5_uint32 swap_bytes, bytes = ctx->buflen;
size_t pad;
/* Now count remaining bytes. */
@@ -113,10 +113,13 @@
pad = bytes >= 56 ? 64 + 56 - bytes : 56 - bytes;
memcpy (&ctx->buffer[bytes], fillbuf, pad);
- /* Put the 64-bit file length in *bits* at the end of the buffer. */
- *(md5_uint32 *) &ctx->buffer[bytes + pad] = SWAP (ctx->total[0] << 3);
- *(md5_uint32 *) &ctx->buffer[bytes + pad + 4] = SWAP ((ctx->total[1] << 3) |
- (ctx->total[0] >> 29));
+ /* Put the 64-bit file length in *bits* at the end of the buffer.
+ Use memcpy to avoid aliasing problems. On most systems, this
+ will be optimized away to the same code. */
+ swap_bytes = SWAP (ctx->total[0] << 3);
+ memcpy (&ctx->buffer[bytes + pad], &swap_bytes, sizeof (swap_bytes));
+ swap_bytes = SWAP ((ctx->total[1] << 3) | (ctx->total[0] >> 29));
+ memcpy (&ctx->buffer[bytes + pad + 4], &swap_bytes, sizeof (swap_bytes));
/* Process last bytes. */
md5_process_block (ctx->buffer, bytes + pad + 8, ctx);
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