Re: [PATCH] err_ptr.h: introduce ERR_PTR_SAFE()

[Amir Goldstein]

On Sat, May 16, 2026 at 10:42 AM David Laight
<david.laight.linux@xxxxxxxxx> wrote:
>
> On Fri, 15 May 2026 21:26:04 +0200
> Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> > On Fri, May 15, 2026 at 8:30 PM David Laight
> > <david.laight.linux@xxxxxxxxx> wrote:
> > >
> > > On Thu, 14 May 2026 22:01:29 +0200
> > > Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> > >
> ...
> > >
> > > The object code bloat would be noticeable if this were used everywhere.
> > > But you could make it a bit simpler:
> > >         if (__builtin_constant_p(__e))
> > >                 BUILD_BUG_ON(__e && !IS_ERR_VALUE(__e));
> > >         else if WARN_ON(__e && !IS_ERR_VALUE(__e))
> > >                 __e = -MAX_ERRNO; // Or maybe -EINVAL to stop and other boundary errors
> > >         (void *)__e;
> >
> > Yeh that's nicer thanks.
>
> Actually this might be better still (or just more succinct):
>         void *__e = (void *)error;
>         BUILD_BUG_ON(!statically_true(IS_ERR_OR_NULL(__e));

This condition is wrong but also my compiler does not evaluate
__builtin_constant_p(IS_ERR_OR_NULL(__e)) as true.

This works
BUILD_BUG_ON(statically_true(!IS_ERR_VALUE(__e)));

I think it is enough to statically assert on ERR_PTR(EINVAL)
and no need to bother with ERR_PTR(0)

>         if (WARN_ON(!IS_ERR_OR_NULL(__e))
>                 __e = (void *)-EINVAL;

Oh, anything but EINVAL please - the most overloaded error value
My choice of meaningful error value would be EFAULT
because without the safe helper we would be returning an address
which is in most likelihood bad, so better be explicit about it.

>         __e;
>
> The WARN_ON() will be optimised away (valid) constants.
>

Yeh this looks nice I'll use this:

#define ERR_PTR_SAFE(error) ({                                  \
        void *__e = (void *)(long)(error);                      \
        BUILD_BUG_ON(statically_true(!IS_ERR_VALUE(__e)));      \
        if (WARN_ON(!IS_ERR_OR_NULL(__e)))                      \
                __e = (void *)(long)-EFAULT;                    \
        __e;                                                    \
})


Thanks!
Amir.