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

[Martin Uecker <uecker@tugraz.at>]

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.

Martin