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

[Martin Uecker <uecker@tugraz.at>]

Am Mittwoch, dem 02.08.2023 um 16:45 +0000 schrieb Qing Zhao:
> 
> > 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?

Right, for a struct with FAM we could check that it is
sizeof () plus a multiple of the element size of the FAM.
Still special logic... 

Martin


> Qing
> > 
> > Martin
> > 
> > 
> > 
> > 
> 

-- 
Univ.-Prof. Dr. rer. nat. Martin Uecker
Graz University of Technology
Institute of Biomedical Imaging