Re: AC_FUNC_MMAP test fails on AIX for MAP_FIXED: who's at fault?

On 2024-07-31 11:05, Zack Weinberg wrote:
> I'd like to ask everyone who reads this message to run
> the test program on operating systems not listed above, and on older
> versions of operating systems that*are* listed above.

I just now tried running it on CheriBSD Morello (cfarm240.cfarm.net) and 
MacOSX 12.6 21.6.0 (cfarm104.cfarm.net) and got OKs straight across. 
(The macOS platform pagesize was 16 KiB rather than the usual 4 KiB.)

One other detail that may trip people up. AIX over-allocates unless you 
set PSALLOC=early in the environment[1], and this can affect how and 
whether mmap works as expected. This is why IBM's POSIX conformance 
statement[2] says you need to have both XPG_SUS_ENV=ON and PSALLOC=early 
in your environment.

Linux over-allocates by default, though you can disable this by fiddling 
with /proc/sys/vm/overcommit*. I don't know how other systems address 
the issue.

[1]: 
https://www.ibm.com/docs/en/aix/7.3?topic=space-configuring-psalloc-environment-variable-early-allocation-mode
[2]: https://www.opengroup.org/csq/repository/RID=ibm%252FXY1%252F2.html