[PATCH] kbuild: add some extra warning flags unconditionally

[Masahiro Yamada]

These flags are documented in the GCC 4.6 manual, and recognized by
Clang as well. Let's rip off the cc-option / cc-disable-warning switches.

Signed-off-by: Masahiro Yamada <yamada....@socionext.com>
---

scripts/Makefile.extrawarn | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 523c4cafe2dc..3ab8d1a303cd 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -23,15 +23,16 @@ warning- := $(empty)
warning-1 := -Wextra -Wunused -Wno-unused-parameter
warning-1 += -Wmissing-declarations
warning-1 += -Wmissing-format-attribute
-warning-1 += $(call cc-option, -Wmissing-prototypes)
+warning-1 += -Wmissing-prototypes
warning-1 += -Wold-style-definition
-warning-1 += $(call cc-option, -Wmissing-include-dirs)
+warning-1 += -Wmissing-include-dirs
warning-1 += $(call cc-option, -Wunused-but-set-variable)
warning-1 += $(call cc-option, -Wunused-const-variable)
warning-1 += $(call cc-option, -Wpacked-not-aligned)
warning-1 += $(call cc-option, -Wstringop-truncation)
-warning-1 += $(call cc-disable-warning, missing-field-initializers)
-warning-1 += $(call cc-disable-warning, sign-compare)
+# The following turn off the warnings enabled by -Wextra
+warning-1 += -Wno-missing-field-initializers
+warning-1 += -Wno-sign-compare

warning-2 := -Waggregate-return
warning-2 += -Wcast-align
@@ -39,8 +40,8 @@ warning-2 += -Wdisabled-optimization
warning-2 += -Wnested-externs
warning-2 += -Wshadow
warning-2 += $(call cc-option, -Wlogical-op)
-warning-2 += $(call cc-option, -Wmissing-field-initializers)
-warning-2 += $(call cc-option, -Wsign-compare)
+warning-2 += -Wmissing-field-initializers
+warning-2 += -Wsign-compare
warning-2 += $(call cc-option, -Wmaybe-uninitialized)
warning-2 += $(call cc-option, -Wunused-macros)

--
2.17.1

[Sedat Dilek]

On Thu, May 9, 2019 at 8:47 AM Masahiro Yamada
<yamada....@socionext.com> wrote:
>
> These flags are documented in the GCC 4.6 manual, and recognized by
> Clang as well. Let's rip off the cc-option / cc-disable-warning switches.
>

BTW, is this a speedup when doing CC/LD FLAGS etc checks unconditionally?
Asking in general - do you have any numbers :-)?

- Sedat -

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[Masahiro Yamada]

On Thu, May 9, 2019 at 4:11 PM Sedat Dilek <sedat...@gmail.com> wrote:
>
> On Thu, May 9, 2019 at 8:47 AM Masahiro Yamada
> <yamada....@socionext.com> wrote:
> >
> > These flags are documented in the GCC 4.6 manual, and recognized by
> > Clang as well. Let's rip off the cc-option / cc-disable-warning switches.
> >
>
> BTW, is this a speedup when doing CC/LD FLAGS etc checks unconditionally?

Yes.
cc-option is somewhat costly because it invoked the compiler to
check if the given flag is supported.

So, I want to get rid of as many cc-option calls as possible.

> Asking in general - do you have any numbers :-)?

Removing a couple of cc-options does not make
a measurable difference in general use-cases.

But, this might be more beneficial for chrome OS
because $(CC) is a wrapper and invoking it is much more expensive.

--
Best Regards
Masahiro Yamada

[Nathan Chancellor]

On Thu, May 09, 2019 at 03:46:35PM +0900, Masahiro Yamada wrote:
> These flags are documented in the GCC 4.6 manual, and recognized by
> Clang as well. Let's rip off the cc-option / cc-disable-warning switches.
>
> Signed-off-by: Masahiro Yamada <yamada....@socionext.com>

Reviewed-by: Nathan Chancellor <natecha...@gmail.com>

[Nick Desaulniers]

From: Masahiro Yamada <yamada....@socionext.com>

> On Thu, May 9, 2019 at 4:11 PM Sedat Dilek <sedat...@gmail.com> wrote:
> > BTW, is this a speedup when doing CC/LD FLAGS etc checks unconditionally?
>
> Yes.
> cc-option is somewhat costly because it invoked the compiler to
> check if the given flag is supported.
>
> So, I want to get rid of as many cc-option calls as possible.
>
>
> > Asking in general - do you have any numbers :-)?
>
> Removing a couple of cc-options does not make
> a measurable difference in general use-cases.
>
> But, this might be more beneficial for chrome OS
> because $(CC) is a wrapper and invoking it is much more expensive.

Android does too, which we plan on removing as we recently measured
the performance cost of 5% for having a Python wrapper to aid in
bisection.

Anyways, I checked these options with clang 4 and gcc 4.6.4 in godbolt.
Tested-by: Nick Desaulniers <ndesau...@google.com>
--
Thanks,
~Nick Desaulniers

[Masahiro Yamada]

Applied to linux-kbuild.