Re: include/linux/thread_info.h:259:25: error: call to '__bad_copy_to' declared with attribute error: copy destination size is too small

[Elizabeth Figura <zfigura@codeweavers.com>]

On Friday, 7 February 2025 06:11:47 CST kernel test robot wrote:
>    In file included from include/linux/spinlock.h:60,
>                     from include/linux/wait.h:9,
>                     from include/linux/wait_bit.h:8,
>                     from include/linux/fs.h:6,
>                     from drivers/misc/ntsync.c:11:
>    In function 'check_copy_size',
>        inlined from 'copy_from_user' at include/linux/uaccess.h:207:7,
>        inlined from 'setup_wait' at drivers/misc/ntsync.c:888:6:
> >> include/linux/thread_info.h:259:25: error: call to '__bad_copy_to' declared with attribute error: copy destination size is too small
>      259 |                         __bad_copy_to();
>          |                         ^~~~~~~~~~~~~~~

This was caught before and mentioned in [1]. The suggestion there of changing "args->count" to "count" doesn't help.

Somehow gcc 12 thinks that the array_size(count, sizeof(*fds)) parameter is constant, although it's finnicky and depends on exactly where __builtin_constant_p() is evaluated.

The bug goes away with gcc 13. Is this worth trying to work around? I don't have any ideas for how to do so.

[1] https://lore.kernel.org/all/21811752-06d3-44cd-b3e6-f8124676df87@app.fastmail.com/