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? But yeah, it _might_ be possible to make objtool a little smarter here. Gimme the .o file and I can take a look tomorrow. -- Josh