On Thu, Jul 25, 2019 at 08:41:25AM -0700, Stephen Boyd wrote: > Quoting Nathan Chancellor (2019-07-24 22:18:57) > > Hi Stephen, > > > > Was the second Kbuild in the subject line supposed to be Kconfig? > > Sure. I'll change it to Kconfig. > > > > > On Wed, Jul 24, 2019 at 04:50:30PM -0700, Stephen Boyd wrote: > > > If the particular version of clang a user has doesn't enable > > > -Werror=unknown-warning-option by default, even though it is the > > > default[1], then make sure to pass the option to the Kconfig cc-option > > > > Hmmm interesting, I did not even know that was possible... Is that a > > clang configuration option or an out of tree patch? Looks like it has > > been on by default since clang 3.2: https://godbolt.org/z/mOmusu > > I asked and it turns out that we force this flag off in the ChromeOS > toolchain so that we can compile the multitude of packages in our system > that assume various GCC specific warning flags. I guess this is easier > than patching all the Makefiles out there. Ah, that makes sense. I forget that most versions of clang have to compile thousands of packages and such. > > > > > > command so that testing options from Kconfig files works properly. > > > Otherwise, depending on the default values setup in the clang toolchain > > > we will silently assume options such as -Wmaybe-uninitialized are > > > supported by clang, when they really aren't. > > > > > > This issue only started happening for me once commit 589834b3a009 > > > ("kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS") was > > > applied on top of commit b303c6df80c9 ("kbuild: compute false-positive > > > -Wmaybe-uninitialized cases in Kconfig"). This leads kbuild to try and > > > > Prior to 589834b3a009, how did cc-option work at all if > > -Wunknown-warning-option wasn't enabled by default? I assume that clang > > would just eat any unknown flags while returning zero so it looked like > > the flag was supported? > > Yes. But just warning options? > > > > > > test for the existence of the -Wmaybe-uninitialized flag with the > > > cc-option command in scripts/Kconfig.include, and it doesn't see an > > > error returned from the option test so it sets the config value to Y. > > > > It might be worth explicitly saying somewhere in here that clang will > > not error on unknown flags without -Werror + -Wunknown-warning-option. > > I think it warns on unknown flags, just not unknown warning options > (-Wfoo), so I didn't mention this. Ah right, duh (it's in the name of the option...), sorry wasn't thinking. > > > > > > Then the makefile tries to pass the unknown option on the command line > > > and -Werror=unknown-warning-option catches the invalid option and breaks > > > the build. > > > > > > Note: this doesn't change the cc-option tests in Makefiles, because > > > those use a different rule that includes KBUILD_CFLAGS by default, and > > > the KBUILD_CFLAGS already has -Werror=unknown-warning-option. Thanks to > > > Doug for pointing out the different rule. > > > > > > [1] https://clang.llvm.org/docs/DiagnosticsReference.html#wunknown-warning-option > > > Cc: Peter Smith <peter.smith@xxxxxxxxxx> > > > Cc: Nathan Chancellor <natechancellor@xxxxxxxxx> > > > Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > > Cc: Douglas Anderson <dianders@xxxxxxxxxxxx> > > > Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx> > > > > > > Change-Id: I3bb69d45bb062d1306acbf19bc0adfb60f706442 > > > > I assume that shouldn't be there? > > > > Overall, seems okay to me (took me a sec to understand the bug, > > certainly a very specific one). It might make sense to explicitly add > > somewhere in the commit message that this syncs cc-option behavior > > between Kconfig and Kbuild as a whole, as I didn't understand that at > > first. Thanks for the triage and sorry for the breakage! > > > > Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx> > > I reworded the commit text a bit now and I'll resend it soon. Thanks for > the review. > Cheers, Nathan
