Messages in this thread | | | Date | Wed, 16 Dec 2020 10:58:55 -0600 | From | Josh Poimboeuf <> | Subject | Re: New objtool warning.. |
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On Wed, Dec 16, 2020 at 10:46:31AM +0000, David Laight wrote: > From: Josh Poimboeuf > > Sent: 16 December 2020 04:49 > > > > On Tue, Dec 15, 2020 at 08:22:23PM -0800, Linus Torvalds wrote: > > > I only see this on my laptop, but that's probably because my desktop > > > is built using clang. So it's a gcc code generation interaction, I > > > suspect.. > > > > > > Anyway, the new warning is > > > > > > drivers/gpu/drm/drm_edid.o: warning: objtool: do_cvt_mode() falls > > > through to next function drm_mode_detailed.isra.0() > > > > > > and googling around a bit I see that 0day ended up reporting it on the > > > linux-next lists, and blames commit 991fcb77f490 ("drm/edid: Fix > > > uninitialized variable in drm_cvt_modes()"). > > > > > > That presumably then makes gcc generate that odd code. > > > > > > That "unreachable()" is because the compiler isn't smart enough to see > > > that yes, there really are case statements for every single possible > > > case. Oh well. Maybe the code should just make one of the possible > > > cases also be the "default:" case, and that might fix it. > > > > > > But maybe this is worth looking into for objtool too? > > > > > > Anyway, I see it with gcc-10.2.1 as per current F32. Holler if you > > > can't reproduce it, I can send the object file around. > > > > I can't recreate with my compiler, but I think I've seen one like this > > before. I suspect s/unreachable()/BUG()/ would fix it? > > Then a smart(er) compiler will report that the BUG() is unreachable.
It shouldn't, BUG() already has unreachable().
-- Josh
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