Re: [PATCH v3 02/10] Add mcheck tests to malloc

[Siddhesh Poyarekar <siddhesh@gotplt.org>]

On 7/6/21 8:20 PM, Stefan Liebler via Libc-alpha wrote:
> Hi Siddhesh,
> 
> starting with this commit, malloc/tst-realloc-mcheck fails if build with
> gcc 7.5 on s390x:
> Error: realloc (NULL, 0) returned NULL.
> 
> With gcc 7.5:
>   p = realloc (NULL, 0);
> realloc is really called, which is using reallochook, which always
> returns NULL:
> static void *
> reallochook (void *ptr, size_t size, const void *caller)
> {
>    if (size == 0)
>      {
>        freehook (ptr, caller);
>        return NULL;
>      }
> 
> With e.g. gcc 9.1:
> malloc(0) is called, which is using mallochook. It is using
> hdr = (struct hdr *) malloc (sizeof (struct hdr) + size + 1);
> ...
> return (void *) (hdr + 1);
> => != NULL
> 
> Can you please have a look? And perhaps also filter out this test?

Thanks, that is an mcheck bug that gcc seems to have masked.  I'll push 
a patch filter it out.  I'll also need to update my hooks patch to fix 
this bug in mcheck.

Thanks,
Siddhesh