Re: "Bad or missing .orc_unwind table. Disabling unwinder." Clang 19 problem? 6.12.8 problem?

[Josh Poimboeuf <jpoimboe@kernel.org>]

On Mon, Jan 13, 2025 at 01:41:24PM -0800, Josh Poimboeuf wrote:
> On Mon, Jan 13, 2025 at 06:29:10PM +0100, Klaus Kusche wrote:
> > 
> > Hello,
> > 
> > I've submitted a bug report to kernel bugzilla,
> > but it was closed with a hint that I should contact
> > the maintainers and LKML.
> > 
> > https://bugzilla.kernel.org/show_bug.cgi?id=219685
> > 
> > You are listed as the maintainers for x86 stack unwinding.
> > Any ideas about that problem before I submit it to LKML?
> > 
> > Is it possibly related to 
> > 
> > https://bugzilla.kernel.org/show_bug.cgi?id=219686
> > 
> > which appeared at the same time?
> > Should it go to the clang maintainers?
> 
> Hi Klaus,
> 
> Thanks for reporting it.  Indeed it's probably related to the build
> warning:
> 
>   vmlinux.o: warning: objtool: start_unlink_intr+0xb7: can't find switch jump table
> 
> It's probably a kernel bug, possibly triggered by the new compiler.
> I'll see if I can recreate.

[adding some folks]

Nathan, I think this is a Clang 19 issue, where one of the jump table
entries is pointing past the end of the function.  When we saw this in
the past I think it was due to some leftover optimization, where the
jump table entry ended up unused so it was harmless.  Are you aware of
any recent bugs in that area?

Maybe objtool should just ignore such entries?

-- 
Josh