Re: [PATCH 5/5] types: Add standard __ob_trap and __ob_wrap scalar types

[Justin Stitt]

Hi,

On Wed, Apr 1, 2026 at 10:38 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Wed, Apr 01, 2026 at 01:52:26PM -0700, Kees Cook wrote:
>
> > (Though I would note that GCC does _not_ refuse the jump when there is a
> > cleanup; it only see the other two uninitialized values.)
>
> Yeah.. I know, but since we also build with clang, any such issue will
> get discovered.
>
> > So that makes it not totally broken, but it does make it a bit fragile.
>
> Right.
>
> > Another concern I have is dealing with older compilers and how to
> > "hide" the label and its code. e.g. if I remove the "goto" from above:
> >
> > ../drivers/misc/lkdtm/bugs.c:1060:1: warning: label 'weird' defined but not used [-Wunused-label]
> >  1060 | weird:
> >       | ^~~~~
> >
> > Oddly, the unreachable code isn't a problem, so we could just wrap the
> > label is some macro like:
> >
> > #define force_label(x) if (0) goto x; x
> >
> > force_label(weird):
> >         pr_info("value: %lu\n", value);
> >         pr_info("outcome: %zu\n", outcome);
> >
>
> __maybe_unused also works on labels. Like:
>
> __overflow: __maybe_unused
>         dead-code-here;
>
>

Completing the loop: Here's the Clang RFC discussing obt label handler
design [1]

[1]: https://discourse.llvm.org/t/rfc-linux-kernel-discusses-overflowbehaviortypes/90486

Jusin