On Mon, Nov 30, 2020 at 2:41 PM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: > > > On Mon, Nov 30, 2020 at 7:42 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > >> > >> 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 >
