Am Sonntag, dem 07.07.2024 um 13:07 +0200 schrieb Alejandro Colomar via Gcc:
> Hi Martin,
>
> On Sun, Jul 07, 2024 at 09:15:23AM GMT, Martin Uecker wrote:
> >
> > Hi Alejandro,
> >
> > if in caller it is known that endptr has access mode "write_only"
> > then it can conclude that the content of *endptr has access mode
> > "none", couldn't it?
>
> Hmmmm. I think you're correct. I'll incorporate that and see how it
> affects the caller.
>
> At first glance, I think it would result in
>
> nptr access(read_only) alias *endptr
> endptr access(write_only) unique
> errno access(read_write) unique
> *endptr access(none) alias nptr
>
> Which is actually having perfect information, regardless of 'restrict'
> on nptr. :-)
Yes, but my point is that even with "restrict" a smarter
compiler could then also be smart enough not to warn even
when *endptr aliases nptr.
>
> > You also need to discuss backwards compatibility. Changing
> > the type of those functions can break valid programs.
>
> I might be forgetting about other possibilities, but the only one I had
> in mind that could break API would be function pointers. However, a
> small experiment seems to say it doesn't:
Right, the outermost qualifiers are ignored, so this is not a
compatibility problem. So I think this is not an issue, but
it is worth pointing it out.
Martin
>
> $ cat strtolp.c
> #include <stdlib.h>
>
> long
> alx_strtol(const char *nptr, char **restrict endptr, int base)
> {
> return strtol(nptr, endptr, base);
> }
>
> typedef long (*strtolp_t)(const char *restrict nptr,
> char **restrict endptr, int base);
> typedef long (*strtolpnr_t)(const char *nptr,
> char **restrict endptr, int base);
>
> int
> main(void)
> {
> [[maybe_unused]] strtolp_t a = &strtol;
> [[maybe_unused]] strtolpnr_t b = &strtol;
> [[maybe_unused]] strtolp_t c = &alx_strtol;
> [[maybe_unused]] strtolpnr_t d = &alx_strtol;
> }
>
> $ cc -Wall -Wextra strtolp.c
> $
>
> Anyway, I'll say that it doesn't seem to break API.
>
> > You would
> > need to make a case that this is unlikely to affect any real
> > world program.
>
> If you have something else in mind that could break API, please let me
> know, and I'll add it to the experiments.
>
> Thanks!
>
> Have a lovely day!
> Alex
>
