Re: objtool failure caused some kernel functionality not working

[Yonghong Song]

On 1/30/25 12:25 AM, Josh Poimboeuf wrote:
> On Wed, Jan 29, 2025 at 11:10:14PM -0800, Yonghong Song wrote:
> > The llvm18 does not have issues. I tried to bisect what changed in llvm19 and
> > found the following llvm patch is responsible:
> >
> > https://github.com/llvm/llvm-project/pull/96089
> >
> > Basically, the compiler might be able to create a jump target which actually
> > not possible at runtime. For example, in one of examples in the above llvm patch, something
> > like
> >     if i >= 3 goto out;  /* i unsigned */
> >     switch i, label default_unreachable:
> >       case 0:  goto label1;
> >       case 1:  goto label2;
> >       case 2:  goto label3;
> >     label1: ...; return;
> >     label2: ...; return;
> >     label3: ...; return;
> >     default_unreachable:
> >
> > I think that this should be a valid code from compiler perspective.
> >
> > Can we fix objtool to handle jump target which is immediately after the func body?Thanks, Yonghong
> I actually have a fix for that, can you try this?
>
>    https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/commit/?h=objtool/core&id=fbb454b7bb39955c324693e73a5cf7e448632553

I applied the above fix and now the kernel works fine and /sys/kernel/debug/tracing/available_filter_functions
can display tracable functions properly.

The fix is in your personal branch. Any plan to send it to upstream repo?

The fix also makes sense to me. So

Tested-by: Yonghong Song <yonghong.song@xxxxxxxxx>
Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>