Re: [C PATCH]: Add Walloc-type to warn about insufficient size in allocations

[Qing Zhao <qing.zhao@oracle.com>]

> On Aug 1, 2023, at 10:31 AM, Martin Uecker <uecker@tugraz.at> wrote:
> 
> Am Dienstag, dem 01.08.2023 um 13:27 +0000 schrieb Qing Zhao:
>> 
>>> On Aug 1, 2023, at 3:51 AM, Martin Uecker via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>>> 
> 
> ....
>>>> Hi Martin,
>>>> Just wondering if it'd be a good idea perhaps to warn if alloc size is
>>>> not a multiple of TYPE_SIZE_UNIT instead of just less-than ?
>>>> So it can catch cases like:
>>>> int *p = malloc (sizeof (int) + 2); // probably intended malloc
>>>> (sizeof (int) * 2)
>>>> 
>>>> FWIW, this is caught using -fanalyzer:
>>>> f.c: In function 'f':
>>>> f.c:3:12: warning: allocated buffer size is not a multiple of the
>>>> pointee's size [CWE-131] [-Wanalyzer-allocation-size]
>>>>    3 |   int *p = __builtin_malloc (sizeof(int) + 2);
>>>>      |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>> 
>>>> Thanks,
>>>> Prathamesh
>>> 
>>> Yes, this is probably a good idea.  It might need special
>>> logic for flexible array members then...
>> 
>> Why special logic for FAM on such warning? (Not a multiple of TYPE_SIZE_UNIT for the element).
>> 
> 
> For
> 
> struct { int n; char buf[]; } *p = malloc(sizeof *p + n);
> p->n = n;
> 
> the size would not be a multiple.

But n is still a multiple of sizeof (char), right? Do I miss anything here?

Qing
> 
> Martin
> 
> 
> 
>