[PATCH v1] Remove 'restrict' from 'nptr' in strtol(3)-like functions

[Alejandro Colomar]

Hi,

On Fri, Jul 05, 2024 at 06:30:50PM GMT, Martin Uecker wrote:
> Am Freitag, dem 05.07.2024 um 17:24 +0100 schrieb Jonathan Wakely:
> > On Fri, 5 Jul 2024 at 17:02, Xi Ruoyao via Gcc <gcc@gcc.gnu.org> wrote:
> > > 
> > > On Fri, 2024-07-05 at 17:53 +0200, Alejandro Colomar wrote:
> > > > At least, I hope there's consensus that while current GCC doesn't warn
> > > > about this, ideally it should, which means it should warn for valid uses
> > > > of strtol(3), which means strtol(3) should be fixed, in all of ISO,
> > > > POSIX, and glibc.
> > > 
> > > It **shouldn't**.  strtol will only violate restrict if it's wrongly
> > > implemented, or something dumb is done like "strtol((const char*) &p,
> > > &p, 0)".
> > > 
> > > See my previous reply.

That's not right.  See my reply to yours, Xi.  The restrict in

	char **endptr

already prevents calls such as strtol(x, x, 0).

The restrict in

	const char *nptr

provides nothing.

> > 
> > Right, is there a valid use of strtol where a warning would be justified?

Is there any valid reason to have restrict in the _first_ parameter of
strtol(3)?  Other than "ISO C says so"?  I'll take my beef with ISO C to
WG14, and hopefully get that fixed.  Can we please discuss this
technically, ignoring the existence of ISO C, for the time being?

> > Showing that you can contrive a case where a const char* restrict and
> > char** restrict can alias doesn't mean there's a problem with strtol.
> 
> I think his point is that a const char* restrict and something which
> is stored in a char* whose address is then passed can alias and there
> a warning would make sense in other situations.   

Indeed.

> But I am also not convinced removing restrict would be an improvement.
> It would make more sense to have an annotation that indicates that
> endptr is only used as output.

What is the benefit of keeping restrict there?  It doesn't provide any
benefits, AFAICS.

I've prepared a paper for wg14.  I'll ask for a number, but will attach
it here already.  I also attach the man(7) source code for it.

Cheers,
Alex

-- 
<https://www.alejandro-colomar.es/>
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