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libiberty/md5: fix strict alias warnings

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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.
This commit is contained in:
Mike Frysinger 2012-07-31 09:02:35 +00:00
parent 4a2608e354
commit 902e433550
2 changed files with 13 additions and 4 deletions
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5
libiberty/ChangeLog
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@ -1,3 +1,8 @@
2012-07-31 Mike Frysinger <vapier@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.
2012-07-26 Kazu Hirata <kazu@codesourcery.com>
Sandra Loosemore <sandra@codesourcery.com>

12
libiberty/md5.c
View File

@ -103,6 +103,7 @@ md5_finish_ctx (struct md5_ctx *ctx, void *resbuf)
{
/* Take yet unprocessed bytes into account. */
md5_uint32 bytes = ctx->buflen;
md5_uint32 swap_bytes;
size_t pad;
/* Now count remaining bytes. */
@ -113,10 +114,13 @@ md5_finish_ctx (struct md5_ctx *ctx, void *resbuf)
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);