On 17/10/2025 11:09 am, Thomas Gleixner wrote:
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> +#define __scoped_masked_user_access(_mode, _uptr, _size, _elbl)
> \
> +for (bool ____stop = false; !____stop; ____stop = true)
> \
> + for (typeof((_uptr)) _tmpptr = __scoped_user_access_begin(_mode, _uptr,
> _size, _elbl); \
> + !____stop; ____stop = true)
> \
> + for (CLASS(masked_user_##_mode##_access, scope) (_tmpptr);
> !____stop; \
> + ____stop = true) \
> + /* Force modified pointer usage within the scope */
> \
> + for (const typeof((_uptr)) _uptr = _tmpptr; !____stop;
> ____stop = true) \
> + if (1)
> +
Truly a thing of beauty. At least the end user experience is nice.
One thing to be aware of is that:
scoped_masked_user_rw_access(ptr, efault) {
unsafe_get_user(rval, &ptr->rval, efault);
unsafe_put_user(wval, &ptr->wval, efault);
} else {
// unreachable
}
will compile. Instead, I think you want the final line of the macro to
be "if (0) {} else" to prevent this.
While we're on the subject, can we find some C standards people to lobby.
C2Y has a proposal to introduce "if (int foo =" syntax to generalise the
for() loop special case. Can we please see about fixing the restriction
of only allowing a single type per loop? This example could be a
single loop if it weren't for that restriction.
Thanks,
~Andrew
