Re: [PATCH] Add build time guard to detect off_t mismatch

[Richard Weinberger <richard@nod.at>]

----- Ursprüngliche Mail -----
> Von: "Jan Kiszka" <jan.kiszka@siemens.com>
> An: "richard" <richard@nod.at>, "xenomai" <xenomai@lists.linux.dev>
> Gesendet: Donnerstag, 7. Mai 2026 14:26:37
> Betreff: Re: [PATCH] Add build time guard to detect off_t mismatch

> On 07.05.26 14:23, Richard Weinberger wrote:
>> When Xenomai is built without _FILE_OFFSET_BITS=64 on a 32 bit system,
>> which is the default, but the Xenomai application itself is built later
>> with _FILE_OFFSET_BITS=64, we get a nasty ABI mismatch. Since only very
>> few cobalt syscalls use off_t, the mismatch goes undiscovered for a
>> surprisingly long time. In my case it surfaced only after a realtime
>> application which uses mmap() failed sometimes at mmap() depending on
>> what functions it called before mmap(). In the good cases it used to
>> work by chance since the extra bytes used for off_t on the stack were
>> zero.
>> 
>> To save the next person in the same situation a lot of time, compute
>> the size of off_t at configure time and compare it against the
>> application's sizeof(off_t) via a static assertion in a new generated
>> header, which is included when building Xenomai applications.
>> 
> 
> This should have been resolved (but apparently we missed most of it) by
> 0bb6608b6fa7129de1ff4213ddf31298616cbf23. Can you name some of the
> remaining mismatches?

In my case it was just mmap(). But wouldn't it hurt at any function
or data structure exposed by Xenomai which uses off_t?

So, I suggest applying my change as safeguard mechanism.

Thanks,
//richard