Fwd: [libiberty] problem with unaligned pointers when using md5_process_bytes

[<piervit at pvittet dot com>]

Hello,

I request your help on the following problem:
Recently, I used the libiberty md5_process_bytes function (for some 
MELT code) and got a problem with it:

I don't know why but on some systems (debian i686) I got some 
unaligned pointers (only when using MELT, I could not reproduce 
elsewhere, so that might come from me or from MELT). Normally, even 
with unaligned pointers, this should works as the function 
md5_process_bytes handles this case:

#if !_STRING_ARCH_unaligned
/* To check alignment gcc has an appropriate operator.  Other
 compilers don't.  */
# if __GNUC__ >= 2
#  define UNALIGNED_P(p) (((md5_uintptr) p) % __alignof__ (md5_uint32) 
!= 0)
# else
#  define UNALIGNED_P(p) (((md5_uintptr) p) % sizeof (md5_uint32) != 
0)
# endif
	len --;
    if (UNALIGNED_P (buffer))
      while (len > 64)
        {
			memcpy (ctx->buffer, buffer, 64);
          md5_process_block (ctx->buffer, 64, ctx);
          buffer = (const char *) buffer + 64;
          len -= 64;
        }
    else
#endif
    md5_process_block (buffer, len & ~63, ctx);
    buffer = (const void *) ((const char *) buffer + (len & ~63));
    len &= 63;
  }

However the handling looks quite strange to me, if UNALIGNED_P 
(buffer) (as this is the case for me) is true, we normally travel the 
while, but then, we execute a new time the line "buffer = (const void 
*) ((const char *) buffer + (len & ~63));", which appear to shift the 
buffer a new time (for more detail, you can have a look at my given gdb 
trace).

I was able to fully compile GCC MELT branch by only adding a pair of 
braces as you can see on the given diff file. I guess this is a bug in 
libiberty (even if I can't understand why my pointer is not aligned).

So can you confirm (or no) that there is a bug in this function (I can 
post to gcc-patches if you think it is a bug), and give me informations 
about how to explain the fact that I get unaligned pointers.

Thanks a lot for your help!

Pierre Vittet

Attachment: md5_process_bytes-gdb_trace.log
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Attachment: md5_process_bytes_works_with_unaligned_ptr-178851.diff
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