Messages in this thread | | | From | Masahiro Yamada <> | Date | Thu, 21 Feb 2019 18:45:05 +0900 | Subject | Re: [PATCH] kbuild: compute false-positive -Wmaybe-uninitialized cases in Kconfig |
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On Thu, Feb 21, 2019 at 6:23 PM Arnd Bergmann <arnd@arndb.de> wrote: > > On Thu, Feb 21, 2019 at 5:14 AM Masahiro Yamada > <yamada.masahiro@socionext.com> wrote: > > > > Since -Wmaybe-uninitialized was introduced by GCC 4.7, we have patched > > various false positives: > > > > - commit e74fc973b6e5 ("Turn off -Wmaybe-uninitialized when building > > with -Os") turned off this option for -Os. > > > > - commit 815eb71e7149 ("Kbuild: disable 'maybe-uninitialized' warning > > for CONFIG_PROFILE_ALL_BRANCHES") turned off this option for > > CONFIG_PROFILE_ALL_BRANCHES > > > > - commit a76bcf557ef4 ("Kbuild: enable -Wmaybe-uninitialized warning > > for "make W=1"") turned off this option for GCC < 4.9 > > Arnd provided more explanation in https://lkml.org/lkml/2017/3/14/903 > > > > I think this looks better by shifting the logic from Makefile to Kconfig. > > > > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> > > I like how this cleans up the logic and documents it better. > I've had my own plans to move this (and most other conditional warning > options) into a header file using the KBUILD_WARN() infrastructure, but > never got around to doing that. I still think that's what we want eventually, > but in the meantime your patch seems fine as well. > > Also, I see that your patch keeps the existing logic, which is good, > but we may want to refine this a little afterwards: > > - we may want to turn off -Wuninitialized for gcc-4.6 and gcc-4.7 > instead of turning off -Wmaybe-uninitialized as we do in the later > compilers.
Ah, right.
I can do that if it is worthwhile.
But, I'd rather want to raise the minimum compiler version than taking care of old compilers. (We will do it eventually.)
> - the proposed CC_OPTIMIZE_FOR_DEBUGGING may need the > same workaround as CC_OPTIMZE_FOR_SIZE.
I know this.
First, my patch took care of CC_OPTIMIZE_FOR_DEBUGGING as well. But, CC_OPTIMIZE_FOR_DEBUGGING was rejected. (https://patchwork.kernel.org/patch/10744541/)
So, I dropped this.
> - For clang, we may want to /not/ turn off -Wmaybe-uninitialized > in all cases. I haven't tried build with with 'clang -Oz > -Wmaybe-uninitialized', but if the number of false positives is small > enough, we could decide to just leave that on.
Does clang recognize -Wmaybe-uninitialized?
I am using Clang I built a few days ago.
masahiro@pug:~$ clang --version clang version 9.0.0 (http://llvm.org/git/clang.git b492883ea31e2046d5725126318911465bc1374f) (http://llvm.org/git/llvm.git 03a15eec9ef44798cd5c57b4ed6a63e62b2c1db6) Target: x86_64-unknown-linux-gnu Thread model: posix InstalledDir: /home/masahiro/toolchains/clang-latest/bin
masahiro@pug:~$ clang -x c /dev/null -Wmaybe-uninitialized -c -o /dev/null warning: unknown warning option '-Wmaybe-uninitialized'; did you mean '-Wuninitialized'? [-Wunknown-warning-option] 1 warning generated.
> Arnd
-- Best Regards Masahiro Yamada
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