Re: [PATCH] c: Split -Wcalloc-transposed-args warning from -Walloc-size, -Walloc-size fixes

[Martin Uecker <uecker@tugraz.at>]

Am Dienstag, dem 19.12.2023 um 09:47 +0100 schrieb Jakub Jelinek:
> On Tue, Dec 19, 2023 at 08:11:11AM +0100, Martin Uecker wrote:
> > Am Montag, dem 18.12.2023 um 20:14 +0100 schrieb Jakub Jelinek:
> > > Hi!
> > > 
> > > The following patch changes -Walloc-size warning to no longer warn
> > > about int *p = calloc (1, sizeof (int));, because as discussed earlier,
> > > the size is IMNSHO sufficient in that case, for alloc_size with 2
> > > arguments warns if the product of the 2 arguments is insufficiently small.
> > > 
> > > Also, it warns also for explicit casts of malloc/calloc etc. calls
> > > rather than just implicit, so not just
> > >   int *p = malloc (1);
> > > but also
> > >   int *p = (int *) malloc (1);
> > > 
> > > It also fixes some ICEs where the code didn't verify the alloc_size
> > > arguments properly (Walloc-size-5.c testcase ICEs with vanilla trunk).
> > > 
> > > And lastly, it introduces a coding style warning, -Wcalloc-transposed-args
> > > to warn for calloc (sizeof (struct S), 1) and similar calls (regardless
> > > of what they are cast to, warning whenever first argument is sizeof and
> > > the second is not).
> > 
> > I would generally see function arguments that are swapped relative
> > to the documented ABI as more than a coding style issue even in 
> > cases where it can be expected to make no difference.
> 
> If you have suggestions how to reword the documentation, would that be
> sufficient for you?  

Maybe simple remove "This is a coding style warning." ?

> I still don't see why given correct alignment one can't
> store struct S into sizeof (struct S) sized heap char array, but if the
> documentation explain reasons why should one write it one way and not the
> other except for coding style, sure.

I do not think we need to argue one way or the other in
the documentation.  

> 
> > > Ok for trunk if this passes bootstrap/regtest?
> > 
> > I wonder whether we could turn on -Walloc-size for -Wall with this change?
> 
> I think that is a possibility, yes.
> 
> BTW, the patch passed bootstrap/regtest on x86_64-linux and i686-linux.
> 
> 	Jakub

Anyway, thank you for fixing / improving this warning!

Martin