Re: WG14 paper for removing restrict from nptr in strtol(3)

[David Malcolm <dmalcolm@redhat.com>]

On Mon, 2024-07-08 at 17:01 +0200, Alejandro Colomar wrote:
> On Mon, Jul 08, 2024 at 10:30:48AM GMT, David Malcolm wrote:
> > > > Why is this change worth
> > > > making? Real-world programs do not make calls like that.
> > > 
> > > Because it makes analysis of 'restrict' more consistent.  The
> > > obvious
> > > improvement of GCC's analyzer to catch restrict violations will
> > > trigger
> > > false positives in normal uses of strtol(3).
> > 
> > Hi Alejandro
> 
> Hi Dave,
> 
> > I'm author/maintainer of GCC's -fanalyzer option, which is
> > presumably
> > why you CCed me on this.
> 
> Yup.
> 
> > One of my GSoC 2022 students (Tim Lange)
> > looked at making use of 'restrict' in -fanalyzer, see e.g. 
> > https://lists.gnu.org/archive/html/bug-gnulib/2022-07/msg00062.html
> > 
> > Based on Paul's comment here:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99860#c2 (and its
> > references) I came to the conclusion at the time that we should
> > work on
> > something else, as the meaning of 'restrict' is too ambiguous.
> 
> restrict, as of the formal definition of ISO C is useless crap.  The
> more I read it, the more I agree.

Please note that "useless crap" was your wording, not mine.

> 
> restrict, as of what -Wrestrict warns about, seems a reasonable
> thing.
> 
> How about a [[gnu::restrict()]] attribute, similar to
> [[gnu::access()]],
> which is simpler than the qualifier?  Since restrict is only
> meaningful
> in function boundaries, it would make sense to have a function
> attribute.  We don't want a qualifier that must follow discarding
> rules.

If it doesn't have the same meaning as "restrict" then perhaps call the
proposed attribute something other than "restrict"?

That said, I don't have strong opinions on any of this, except to note
that I have more than enough *other* work on improvements to GCC's
static analyzer and usability to keep me busy, so getting sucked into
discussion/implementation on 'restrict' is something I want to avoid,
and -Wanalyzer-overlapping-buffers is getting the job done for me at
the moment.

[...snip...]

Hope this is constructive; sorry again if I missed anything due to only
skimming the thread

Dave