On Mon, Mar 20, 2023 at 11:53:37AM -0700, Nathan Chancellor wrote: > On Mon, Mar 20, 2023 at 11:26:17AM -0700, Linus Torvalds wrote: > > On Mon, Mar 20, 2023 at 11:05 AM Nathan Chancellor <nathan@xxxxxxxxxx> wrote: > > > > > > On the clang front, I am still seeing the following warning turned error > > > for arm64 allmodconfig at least: > > > > > > drivers/gpu/host1x/dev.c:520:6: error: variable 'syncpt_irq' is uninitialized when used here [-Werror,-Wuninitialized] > > > if (syncpt_irq < 0) > > > ^~~~~~~~~~ > > > > Hmm. I do my arm64 allmodconfig builds with gcc, and I'm surprised > > that gcc doesn't warn about this. > > Perhaps these would make doing allmodconfig builds with clang more > frequently less painful for you? > > https://lore.kernel.org/llvm/20230319235619.GA18547@dev-arch.thelio-3990X/ > > > That syncpt_irq thing isn't written to anywhere, so that's pretty egregious. > > > > We use -Wno-maybe-uninitialized because gcc gets it so wrong, but > > that's different from the "-Wuninitialized" thing (without the > > "maybe"). > > > > I've seen gcc mess this up when there is one single assignment, > > because then the SSA format makes it *so* easy to just use that > > assignment out-of-order (or unconditionally), but this case looks > > unusually clear-cut. > > > > So the fact that gcc doesn't warn about it is outright odd. > > > > > If that does not come to you through other means before -rc4, could you > > > just apply it directly so that I can stop applying it to our CI? :) > > > > Bah. I took it now, there's no excuse for that thing. > > Thanks! > > > Do we have any gcc people around that could explain why gcc failed so > > miserably at this trivial case? > > Cc'ing linux-toolchains. The start of the thread is here: > > https://lore.kernel.org/CAHk-=wgSqpdkeJBb92M37JNTdRQJRnRUApraHKE8uGHTqQuu2Q@xxxxxxxxxxxxxx/ > > The problematic function before the fix is here: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/host1x/dev.c?id=3d3699bde4b043eea17993e4e76804a8128f0fdb#n487 > > I will see if I have some cycles to try and reduce something out for the > GCC folks. While setting up the reduction, I noticed that there is an instance of -Wmaybe-uninitialized at this site. Seems odd that it is not sure, I will reduce on that. ../drivers/gpu/host1x/dev.c: In function 'host1x_probe': ../drivers/gpu/host1x/dev.c:520:12: error: 'syncpt_irq' may be used uninitialized [-Werror=maybe-uninitialized] 520 | if (syncpt_irq < 0) | ^ ../drivers/gpu/host1x/dev.c:490:13: note: 'syncpt_irq' was declared here 490 | int syncpt_irq; | ^~~~~~~~~~ cc1: all warnings being treated as errors Cheers, Nathan
