| From 8eeb9da6d017761037bf757780ea544dfeabbad8 Mon Sep 17 00:00:00 2001 |
| From: Mike Frysinger <vapier@gentoo.org> |
| Date: Tue, 31 Jul 2012 09:02:35 +0000 |
| Subject: [PATCH] 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. |
| --- |
| libiberty/ChangeLog | 5 +++++ |
| libiberty/md5.c | 12 ++++++++---- |
| 2 files changed, 13 insertions(+), 4 deletions(-) |
| |
| 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. |
| |
| diff --git a/libiberty/md5.c b/libiberty/md5.c |
| index 0db8fc8..8cc0cb5 100644 |
| --- a/src/md5.c |
| +++ b/src/md5.c |
| @@ -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); |
| -- |
| 1.8.2.1 |
| |