Re: AC_FUNC_MMAP lacks <unistd.h> include?

[Florian Weimer]

* Paul Eggert:

> On 2023-05-17 11:14, Florian Weimer wrote:
> +#ifndef getpagesize
>>> +# ifdef _SC_PAGESIZE
>>> +#  define getpagesize() sysconf (_SC_PAGESIZE)
>>> +# elif defined _SC_PAGE_SIZE
>>> +#  define getpagesize() sysconf (_SC_PAGE_SIZE)
>>> +# elif HAVE_GETPAGESIZE
>>> +int getpagesize ();
>> Isn't this a bit weird?  Why can't we rely on the HAVE_GETPAGESIZE
>> check?
>
> POSIX has standardized on sysconf; it no longer specifies
> getpagesize. Also, getpagesize doesn't work for page sizes greater
> than INT_MAX. For both reasons, it's better to prefer sysconf to
> getpagesize nowadays. I installed the attached patch to try to make
> this clearer.

But then HAVE_GETPAGESIZE probably should not succeed spuriously because
of an implicit function declaration.

I still suspect there is something peculiar to libgtop that triggers
this, such as some late -D_XOPEN_SOURCE somewhere, or conditional
execution of the HAVE_UNISTD_H check.

Thanks,
Florian