Re: [patch] Cleanup: don't call free(NULL) unnecessarily

[Thomas Schwinge <thomas at codesourcery dot com>]

Hi!

On Tue, 05 Mar 2013 11:18:01 -0800, Paul Pluzhnikov <ppluzhnikov@google.com> wrote:
> This patch eliminates calls to free(NULL) from within vfprintf.
> 
> This is desirable because e.g. fprintf(stderr, ...) is often called from
> signal handlers, and while technically illegal, this tends to work.
> 
> Glibc free(NULL) also works in signal context, but end user could supply
> his own malloc/free, which may not.
> 
> The same check was already done on e.g. line 1648.

> --- a/stdio-common/vfprintf.c
> +++ b/stdio-common/vfprintf.c
> @@ -1691,7 +1691,8 @@ do_positional:
>      /* Just a counter.  */
>      size_t cnt;
>  
> -    free (workstart);
> +    if (__builtin_expect (workstart != NULL, 0))
> +      free (workstart);

Given that in the past, for example, in commits
62605cbfcb3d2f118c9f64ce049220b82928e6d4 and
72e6cdfa2cd95240439c72705ab28a2eebb7d04e (ChangeLog in commit
0726cdf7dbdccdf0f99d910d5e7799d902a1ec38) such checks have been removed,
does this (and likewise for other cases) warrant a comment being added,
or some other form of (user-accessible) documentation update what this
change achieves?


GrÃÃe,
 Thomas

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