linux-kernel - Re: [PATCH] Makefile: remove stale cc-option checks

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Date:   Sat, 14 Aug 2021 10:33:01 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Vitor Massaru Iha <vitor@...saru.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Daniel Latypov <dlatypov@...gle.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] Makefile: remove stale cc-option checks

On Wed, Aug 11, 2021 at 8:01 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> On Tue, Aug 10, 2021 at 01:42:37PM -0700, Nick Desaulniers wrote:
> > cc-option, cc-option-yn, and cc-disable-warning all invoke the compiler
> > during build time, and can slow down the build when these checks become
> > stale for our supported compilers, whose minimally supported versions
> > increases over time. See Documentation/process/changes.rst for the
> > current supported minimal versions (GCC 4.9+, clang 10.0.1+). Compiler
> > version support for these flags may be verified on godbolt.org.
> >
> > The following flags are GCC only and supported since at least GCC 4.9.
> > Remove cc-option and cc-disable-warning tests.
> > * -fno-tree-loop-im
> > * -Wno-maybe-uninitialized
> > * -fno-reorder-blocks
> > * -fno-ipa-cp-clone
> > * -fno-partial-inlining
> > * -femit-struct-debug-baseonly
> > * -fno-inline-functions-called-once
> > * -fconserve-stack
> >
> > The following flags are supported by all supported versions of GCC and
> > Clang. Remove their cc-option, cc-option-yn, and cc-disable-warning tests.
> > * -fno-delete-null-pointer-checks
> > * -fno-var-tracking
> > * -mfentry
> > * -Wno-array-bounds
> >
> > The following configs are made dependent on GCC, since they use GCC
> > specific flags.
> > * READABLE_ASM
> > * DEBUG_SECTION_MISMATCH
> >
> > --param=allow-store-data-races=0 was renamed to --allow-store-data-races
> > in the GCC 10 release.
> >
> > Also, base RETPOLINE_CFLAGS and RETPOLINE_VDSO_CFLAGS on CONFIC_CC_IS_*
> > then remove cc-option tests for Clang.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1436
> > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
>
> Fewer pointless calls to the compiler is always a good thing :)
>
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
>
> Small comments inline.
>
> > ---
> > Note: It may be preferred to move the test for
> > -fno-inline-functions-called-once for DEBUG_SECTION_MISMATCH into
> > Kconfig. That one does seem relatively more reasonable to implement in
> > Clang.
> >
> >  Makefile          | 55 ++++++++++++++++++++++++++---------------------
> >  lib/Kconfig.debug |  2 ++
> >  2 files changed, 33 insertions(+), 24 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 027fdf2a14fe..3e3fb4affba1 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -730,9 +730,10 @@ endif # KBUILD_EXTMOD
> >  # Defaults to vmlinux, but the arch makefile usually adds further targets
> >  all: vmlinux
> >
> > -CFLAGS_GCOV  := -fprofile-arcs -ftest-coverage \
> > -     $(call cc-option,-fno-tree-loop-im) \
> > -     $(call cc-disable-warning,maybe-uninitialized,)
> > +CFLAGS_GCOV  := -fprofile-arcs -ftest-coverage
> > +ifdef CONFIG_CC_IS_GCC
> > +CFLAGS_GCOV  += -fno-tree-loop-im
> > +endif
>
> Eliminating -Wno-maybe-uninitialized might warrant a comment in the
> commit message as I was initially confused then I realized that it is
> unconditionally added later.


Indeed.

Commit 78a5255ffb6a1af189a83e493d916ba1c54d8c75
could have removed -Wno-maybe-initialized
from CFLAGS_GCOV as well, but somehow it has been
left over here...


Comments in the commit log, or perhaps
splitting this as 1/2 will be less confusing.





-- 
Best Regards
Masahiro Yamada