Re: [PATCH 07/17] Regex: Additional memory management checks.

[Paul Eggert]

On 12/08/2017 01:16 AM in 
<https://sourceware.org/ml/libc-alpha/2017-12/msg00242.html> Arnold 
Robbins wrote:
> +  /* some malloc()-checkers don't like zero allocations */
> +  if (preg->re_nsub > 0)
>     dfa->subexp_map = re_malloc (int, preg->re_nsub);
> +  else
> +    dfa->subexp_map = NULL;

Which checkers are these? Can they be told that 'malloc (0)' is OK? 
Since the code here is fine (i.e. it will work even if 'malloc (0)' 
succeeds and returns NULL) it may be better to leave the code alone and 
to fix the checkers instead.

> +   * ADR: valgrind says size can be 0, which then doesn't
> +   * free the block of size 0.  Harumph. This seems
> +   * to work ok, though.
> +   */
> +  if (size == 0)
> +    {
> +       memset(set, 0, sizeof(*set));
> +       return REG_NOERROR;
> +    }
>     set->alloc = size;
>     set->nelem = 0;
>     set->elems = re_malloc (int, size);

For this, how about if we use the corresponding Gnulib fix instead? An 
advantage of the Gnulib fix is that it doesn't introduce runtime 
overhead when glibc is used. Here is a URL:

https://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=bbf0d723ed2335add96bcc0f842885d8a5d8b6da

> diff --git a/posix/regexec.c b/posix/regexec.c
> index 2d2bc46..8573765 100644
> --- a/posix/regexec.c
> +++ b/posix/regexec.c
> @@ -605,7 +605,7 @@ re_search_internal (const regex_t *preg, const char 
> *string, int length,
>     nmatch -= extra_nmatch;
>   
>     /* Check if the DFA haven't been compiled.  */
> -  if (BE (preg->used == 0 || dfa->init_state == NULL
> +  if (BE (preg->used == 0 || dfa == NULL || dfa->init_state == NULL
>           || dfa->init_state_word == NULL || dfa->init_state_nl == NULL
>           || dfa->init_state_begbuf == NULL, 0))
>       return REG_NOMATCH;

Why is this change needed? I couldn't see a code path that would trigger 
it. Obviously I'm missing something. I suggest mentioning the reason in 
the comment.