[PATCH] simplify expand_tcbtab/alloc_tcb

[Dmitry V. Levin]

On Tue, Jun 21, 2011 at 08:21:26PM +0200, Denys Vlasenko wrote:
> Hi,
> 
> Sometime ago expand_tcbtab/alloc_tcb were modified
> so that they never return failure (they will abort instead).
> 
> This opens up a possibility for further simplifications.
> 
> This patch is a simple one which gets rid of a few
> intermediate variables, simplifies a few expressions,
> and uses error_msg_and_die instead of more verbose
> fprintf+cleanup+exit sequence.
> 
> In alloc_tcp, I use memset to clear entire new tcp.
> This not only saves a few bytes of code, but lowers chances
> of future bugs where some data "leaks out" into new tcb's
> from old ones because we forgot to re-initialize it.
> 
> Patch should be fairly safe, but please review anyway.
> -- 
> vda
> 
> diff -d -urpN strace.6/strace.c strace.7/strace.c
> --- strace.6/strace.c	2011-06-21 20:12:03.206604267 +0200
> +++ strace.7/strace.c	2011-06-21 20:11:27.220751557 +0200
> @@ -1252,21 +1252,14 @@ expand_tcbtab(void)
>  	   callers have pointers and it would be a pain.
>  	   So tcbtab is a table of pointers.  Since we never
>  	   free the TCBs, we allocate a single chunk of many.  */
> -	struct tcb **newtab = (struct tcb **)
> -		realloc(tcbtab, 2 * tcbtabsize * sizeof tcbtab[0]);
> -	struct tcb *newtcbs = (struct tcb *) calloc(tcbtabsize,
> -						    sizeof *newtcbs);
> -	int i;
> -	if (newtab == NULL || newtcbs == NULL) {
> -		fprintf(stderr, "%s: expand_tcbtab: out of memory\n",
> -			progname);
> -		cleanup();
> -		exit(1);
> -	}
> -	for (i = tcbtabsize; i < 2 * tcbtabsize; ++i)
> -		newtab[i] = &newtcbs[i - tcbtabsize];
> +	int i = tcbtabsize;
> +	struct tcb *newtcbs = calloc(tcbtabsize, sizeof newtcbs[0]);
>  	tcbtabsize *= 2;
> -	tcbtab = newtab;
> +	tcbtab = realloc(tcbtab, tcbtabsize * sizeof tcbtab[0]);

No, this intermediate newtab is still necessary because cleanup() uses
tcbtab.  For the same reason, tcbtabsize could be changed only when
tcbtab is already updated, e.g.
	tcbtab = newtab;
	tcbtabsize = newtabsize;


-- 
ldv
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