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

On 07.05.26 14:32, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
>> Von: "Jan Kiszka" <[email protected]>
>> An: "richard" <[email protected]>, "xenomai" <[email protected]>
>> 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.
> 

mmap is supposed to be fine by now. So we need to understand why it is
not and resolve the issue - or my other patch would be pointless.

Jan

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