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From: Florian Weimer <fweimer@redhat.com>
To: Siddhesh Poyarekar via Libc-alpha <libc-alpha@sourceware.org>
Cc: Siddhesh Poyarekar <siddhesh@sourceware.org>
Subject: Re: [PATCH] Handle NULL input to malloc_usable_size [BZ #28506]
References: <20211029031802.254600-1-siddhesh@sourceware.org>
Date: Fri, 29 Oct 2021 10:30:46 +0200
In-Reply-To: <20211029031802.254600-1-siddhesh@sourceware.org> (Siddhesh
 Poyarekar via Libc-alpha's message of "Fri, 29 Oct 2021 08:48:02
 +0530")
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* Siddhesh Poyarekar via Libc-alpha:

>  size_t
>  __malloc_usable_size (void *m)
>  {
> +  size_t result =3D 0;
> =20
> +  if (m !=3D NULL)
> +    result =3D musable (m);
>    return result;
>  }

Is there a reason for not writing it this way?

size_t
__malloc_usable_size (void *m)
{
  if (m =3D=3D NULL)
    return 0;
  return musable (m);
}

The extra variable seems a bit =E2=80=A6 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>
> =20
>  static int
>  do_test (void)
>  {
>    size_t usable_size;
>    void *p =3D malloc (7);
> =20
> +  TEST_VERIFY_EXIT (p !=3D NULL);
>    usable_size =3D malloc_usable_size (p);
> +  TEST_VERIFY_EXIT (usable_size =3D=3D 7);

You can use TEST_COMPARE here.

>    memset (p, 0, usable_size);
>    free (p);
> +
> +  TEST_VERIFY_EXIT (malloc_usable_size (NULL) =3D=3D 0);

And here.

Thanks,
Florian