bug#716: Bug in buffer-swap-text

[Jason Rumney <jasonr@f2s.com>]

Stefan Monnier wrote:
> Your analysis sounds right, thank you.  I'd suggest to use another
> r_alloc primitve, something like r_alloc_reset_variable, so you could do
>
>   r_alloc_reset_variable(&current_buffer->own_text.beg);
>   r_alloc_reset_variable(&other_buffer->own_text.beg);
>
> after the swap.  It could use the untested patch below.  WDYT?
>
>
> === modified file 'src/ralloc.c'
> --- src/ralloc.c	2008-11-21 19:14:07 +0000
> +++ src/ralloc.c	2008-12-23 17:23:02 +0000
> @@ -402,7 +402,7 @@
>  
>    while (p != NIL_BLOC)
>      {
> -      if (p->variable == ptr && p->data == *ptr)
> +      if (p->data == *ptr)
>  	return p;
>  
>        p = p->next;
>   
This removes the consistency check, without which we would have taken 
much longer to find this problem, as Emacs would not have aborted when 
no bloc could be found, and the problem would have been memory 
corruption later when that bloc of memory was moved and the wrong 
pointer updated.