Re: [PATCH] Handle NULL input to malloc_usable_size [BZ #28506]

[Florian Weimer <fweimer@redhat.com>]

* Siddhesh Poyarekar via Libc-alpha:

>  size_t
>  __malloc_usable_size (void *m)
>  {
> +  size_t result = 0;
>  
> +  if (m != NULL)
> +    result = musable (m);
>    return result;
>  }

Is there a reason for not writing it this way?

size_t
__malloc_usable_size (void *m)
{
  if (m == NULL)
    return 0;
  return musable (m);
}

The extra variable seems a bit … unnecessary?

> diff --git a/malloc/tst-malloc-usable.c b/malloc/tst-malloc-usable.c
> index a1074b782a..cd5c27cfcd 100644
> --- a/malloc/tst-malloc-usable.c
> +++ b/malloc/tst-malloc-usable.c
> @@ -21,29 +21,24 @@
>  #include <malloc.h>
>  #include <string.h>
>  #include <stdio.h>
> +#include <support/support.h>
> +#include <support/check.h>
>  
>  static int
>  do_test (void)
>  {
>    size_t usable_size;
>    void *p = malloc (7);
>  
> +  TEST_VERIFY_EXIT (p != NULL);
>    usable_size = malloc_usable_size (p);
> +  TEST_VERIFY_EXIT (usable_size == 7);

You can use TEST_COMPARE here.

>    memset (p, 0, usable_size);
>    free (p);
> +
> +  TEST_VERIFY_EXIT (malloc_usable_size (NULL) == 0);

And here.

Thanks,
Florian