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Re: PRecord sets memory even when it says it did not


On Mon, Sep 14, 2009 at 11:36 AM, Pedro Alves <pedro@codesourcery.com> wrote:
> Hmmm. ?On a less quicker look, how about if we get rid of the
> dcache_xfer_memory and dcache_update calls in memory_xfer_partial,
>
> (excuse the pseudo-patch-written-in-email)
>
> target.c:memory_xfer_partial
>
> - ?inf = find_inferior_pid (ptid_get_pid (inferior_ptid));
> -
> - ?if (inf != NULL
> - ? ? ?&& (region->attrib.cache
> - ? ? ? ? || (stack_cache_enabled_p && object == TARGET_OBJECT_STACK_MEMORY)))
> - ? ?{
> - ? ? ?if (readbuf != NULL)
> - ? ? ? res = dcache_xfer_memory (ops, target_dcache, memaddr, readbuf,
> - ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? reg_len, 0);
> - ? ? ?else
> - ? ? ? /* FIXME drow/2006-08-09: If we're going to preserve const
> - ? ? ? ? ?correctness dcache_xfer_memory should take readbuf and
> - ? ? ? ? ?writebuf. ?*/
> - ? ? ? res = dcache_xfer_memory (ops, target_dcache, memaddr,
> - ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? (void *) writebuf,
> - ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? reg_len, 1);
> - ? ? ?if (res <= 0)
> - ? ? ? return -1;
> - ? ? ?else
> - ? ? ? {
> - ? ? ? ? if (readbuf && !show_memory_breakpoints)
> - ? ? ? ? ? breakpoint_restore_shadows (readbuf, memaddr, reg_len);
> - ? ? ? ? return res;
> - ? ? ? }
> - ? ?}
> -
> - ?/* Make sure the cache gets updated no matter what - if we are writing
> - ? ? to the stack, even if this write is not tagged as such, we still need
> - ? ? to update the cache. */
> -
> - ?if (inf != NULL
> - ? ? ?&& readbuf == NULL
> - ? ? ?&& !region->attrib.cache
> - ? ? ?&& stack_cache_enabled_p
> - ? ? ?&& object != TARGET_OBJECT_STACK_MEMORY)
> - ? ?{
> - ? ? ?dcache_update (target_dcache, memaddr, (void *) writebuf, reg_len);
> - ? ?}
>
>
> and replaced this call below, something like so:
>
> ?do
> ? ?{
> - ? ? ?res = ops->to_xfer_partial (ops, TARGET_OBJECT_MEMORY, NULL,
> - ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? readbuf, writebuf, memaddr, reg_len);
> + ? ? ?res = dcache_xfer_partial (ops, TARGET_OBJECT_MEMORY, NULL,
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? readbuf, writebuf, memaddr, reg_len);
>
>
> ? ? ?if (res > 0)
> ? ? ? ?break;
>
> ? ? ?/* We want to continue past core files to executables, but not
> ? ? ? ? past a running target's memory. ?*/
> ? ? ?if (ops->to_has_all_memory (ops))
> ? ? ? ?break;
>
> ? ? ?ops = ops->beneath;
> ? ?}
> ?while (ops != NULL);
>
> ... by a dcache_xfer_memory call, but tweak its interface to pass it
> the object type? ?Things would be tidier and dcache_xfer_memory
> would then handle all this dcache updating/invalidating itself.
>
> On the plus side, when the dcache is in effect, with that change,
> we'd again walk the whole target stack, which isn't true currently
> (and looks like a possible design flaw).

OTOH, its nice having memory_xfer_partial do the region attribute processing.

It seems like what's needed is to move

  /* Make sure the cache gets updated no matter what - if we are
writing
     to the stack, even if this write is not tagged as such, we still
need
     to update the cache. */

  if (inf != NULL
      && readbuf == NULL
      && !region->attrib.cache
      && stack_cache_enabled_p
      && object != TARGET_OBJECT_STACK_MEMORY)
    {
      dcache_update (target_dcache, memaddr, (void *) writebuf, reg_len);
    }

to after the call

      res = ops->to_xfer_partial (ops, TARGET_OBJECT_MEMORY, NULL,
                                  readbuf, writebuf, memaddr, reg_len);

predicated on res > 0.

[dcache.c does the write first, and then updates the cache if it
succeeded, we just need to do that here too, methinks]


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