Re: [patch] only update dcache after write succeeds

[Michael Snyder <msnyder at vmware dot com>]

Doug Evans wrote:
> Hi.
>
> Marc, Greg: Can you see if this patch fixes things for you?

Hey Doug,

I tested this change, and it does indeed seem to fix the problem
with target record -- but.   ;-)

Part of the reason that it works is that record_xfer_partial
calls error() instead of returning -1.  If I change it so that
it returns -1, things get more complicated.

The do-while loop that used to follow and now preceeds this code
calls target-beneath, which in our case results in several different
target methods being called, one of which eventually returns > 0.

That just means that in the present case, calling error is correct.
But I worry about some of the other cases where the target method
returns -1, and whether badness might occur in some other cases.

Michael


> 2009-09-14  Doug Evans  <dje@google.com>
>
> 	* target.c (memory_xfer_partial): Only update dcache after we know
> 	the write succeeded.
>
> Index: target.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/target.c,v
> retrieving revision 1.223
> diff -u -p -r1.223 target.c
> --- target.c	8 Sep 2009 23:52:45 -0000	1.223
> +++ target.c	14 Sep 2009 19:11:38 -0000
> @@ -1289,19 +1289,6 @@ memory_xfer_partial (struct target_ops *
>  	}
>      }
>  
> -  /* 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);
> -    }
> -
>    /* If none of those methods found the memory we wanted, fall back
>       to a target partial transfer.  Normally a single call to
>       to_xfer_partial is enough; if it doesn't recognize an object
> @@ -1331,6 +1318,20 @@ memory_xfer_partial (struct target_ops *
>    if (readbuf && !show_memory_breakpoints)
>      breakpoint_restore_shadows (readbuf, memaddr, reg_len);
>  
> +  /* 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 (res > 0
> +      && inf != NULL
> +      && writebuf != NULL
> +      && !region->attrib.cache
> +      && stack_cache_enabled_p
> +      && object != TARGET_OBJECT_STACK_MEMORY)
> +    {
> +      dcache_update (target_dcache, memaddr, (void *) writebuf, reg_len);
> +    }
> +
>    /* If we still haven't got anything, return the last error.  We
>       give up.  */
>    return res;