On Mon, Nov 30, 2020 at 2:41 PM Toke Høiland-Jørgensen [off-list ref] wrote:

Andrii Nakryiko [off-list ref] writes:

quoted

On Mon, Nov 30, 2020 at 7:42 AM Toke Høiland-Jørgensen [off-list ref] wrote:

quoted

The kernel feature probing results in 'errno' being set if the probing
fails (as is often the case). This can stick around and leak to the caller,
which can lead to confusion later. So let's make sure we always reset errno
after calling a probe function.

What specifically is the problem and what sort of confusion we are
talking about here? You are not supposed to check errno, unless the
function returned -1 or other error result.

In some cases, you have to reset errno manually just to avoid
confusion (see how strtol() is used, as an example).

I.e., I don't see the problem here, any printf() technically can set
errno to <0, we don't reset errno after each printf call though,
right?

Well yeah, technically things work fine in the common case. But this

It works fine in all cases. Assuming "errno != 0 means last
libc/syscall failed" is just wrong.

errno thing sent me on quite the wild goose chase when trying to find
the root cause of the pinning issue I also sent a patch for...

So since reseting errno doesn't hurt either I figured I'd save others
ending up in similar trouble. If it's not to your taste feel free to
just drop the patch :)

Yep, let's just drop it, no need to create a bad precedent.

-Toke