[patch, ia64] Fix unaligned accesses on IA64 from dwarf2out.c

[Pedro Alves]

On Wednesday 10 August 2011 01:02:50, Steve Ellcey wrote:
> On Tue, 2011-08-09 at 16:50 -0700, Richard Henderson wrote:
> > > 
> > > I think I like using a union to ensure the alignment of checksum better.
> > > In dwarf2out.c we are always using one md5_ctx structure and one
> > > checksum buffer but in fold-const.c there are routines where we use one
> > > md5_ctx structure with 4 (fold_build2_stat_loc) or 6
> > > (fold_build3_stat_loc) different checksum buffers.
> > 
> > I'm not keen on this.
> > 
> > Yes, it does happen to work, but only accidentally.  The CTX
> > object and the CHECKSUM object have overlapping lifetimes
> > within md5_read_ctx.
> > 
> > 
> > r~
> 
> I am not proposing we put the CTX object and the CHECKSUM object into
> one union.  I am proposing we leave the CTX object alone and put the
> CHECKSUM object in a union with a dummy variable of type md5_uint32 in
> order to ensure that the CHECKSUM object has the correct alignment.
> 
> So the usage would be:
> 
> union md5_resbuf
> {
>   md5_uint32 dummy;                     /* Unused variable used to ensure alignment */
>   unsigned char resbuf[16];             /* The buffer we are using in md5_finish_ctx */
> };

Or even

union md5_resbuf
{
  md5_uint32 ui32[4];
  unsigned char ui8[16];
};

and put it in include/md5.h instead, so that all clients
can use it instead of cooking up the same themselves.
liberty's md5.c itself internaly could be make to use the
union instead of the casts?

*looks for users of md5*

but then, gold does:

  unsigned char* ov = of->get_output_view(this->build_id_note_->offset(),
                                          this->build_id_note_->data_size());

  const char* style = parameters->options().build_id();
  if (strcmp(style, "sha1") == 0)
    {
      sha1_ctx ctx;
      sha1_init_ctx(&ctx);
      sha1_process_bytes(iv, this->output_file_size_, &ctx);
      sha1_finish_ctx(&ctx, ov);
    }
  else if (strcmp(style, "md5") == 0)
    {
      md5_ctx ctx;
      md5_init_ctx(&ctx);
      md5_process_bytes(iv, this->output_file_size_, &ctx);
      md5_finish_ctx(&ctx, ov);

which makes me wonder if the right fix isn't to change
libiberty internally to not rely on the alignment.

libiberty's sha1 routines seem to have the same issue
(though they don't appear used in gcc.  gold uses them, as
seen above).

-- 
Pedro Alves