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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
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Current libiberty md5 code triggers these warnings with gcc-4.7.1 for me:
libiberty/md5.c: In function âmd5_finish_ctxâ:
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
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