linux-kernel - Re: [PATCH 2/2] kbuild: move CFLAGS_{KASAN,UBSAN,KCSAN} exports to relevant Makefiles

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Date:   Thu, 10 Sep 2020 16:12:01 +0200
From:   Marco Elver <elver@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH 2/2] kbuild: move CFLAGS_{KASAN,UBSAN,KCSAN} exports to
 relevant Makefiles

On Thu, 10 Sep 2020 at 15:45, Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> Move CFLAGS_KASAN*, CFLAGS_UBSAN, CFLAGS_KCSAN to Makefile.kasan,
> Makefile.ubsan, Makefile.kcsan, respectively.
>
> This commit also avoids the same -fsanitize=* flags being added to
> CFLAGS_UBSAN multiple times.
>
> Prior to this commit, the ubsan flags were appended by the '+='
> operator, without any initialization. Some build targets such as
> 'make bindeb-pkg' recurses to the top Makefile, and ended up with
> adding the same flags to CFLAGS_UBSAN twice.
>
> Clear CFLAGS_UBSAN with ':=' to make it a simply expanded variable.
> This is better than a recursively expanded variable, which evaluates
> $(call cc-option, ...) multiple times before Kbuild starts descending
> to subdirectories.
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
>  Makefile               | 1 -
>  scripts/Makefile.kasan | 2 ++
>  scripts/Makefile.kcsan | 2 +-
>  scripts/Makefile.ubsan | 3 +++
>  4 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index ec2330ce0fc5..4b5a305e30d2 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -517,7 +517,6 @@ export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
>
>  export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
>  export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
> -export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN CFLAGS_KCSAN
>  export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
>  export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
>  export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
> diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
> index 1532f1a41a8f..1e000cc2e7b4 100644
> --- a/scripts/Makefile.kasan
> +++ b/scripts/Makefile.kasan
> @@ -47,3 +47,5 @@ CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
>                 $(instrumentation_flags)
>
>  endif # CONFIG_KASAN_SW_TAGS
> +
> +export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE
> diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan
> index c50f27b3ac56..cec50d74e0d0 100644
> --- a/scripts/Makefile.kcsan
> +++ b/scripts/Makefile.kcsan
> @@ -9,7 +9,7 @@ endif
>
>  # Keep most options here optional, to allow enabling more compilers if absence
>  # of some options does not break KCSAN nor causes false positive reports.
> -CFLAGS_KCSAN := -fsanitize=thread \
> +export CFLAGS_KCSAN := -fsanitize=thread \
>         $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) \
>         $(call cc-option,$(call cc-param,tsan-instrument-read-before-write=1)) \
>         $(call cc-param,tsan-distinguish-volatile=1)

This doesn't apply to -next, which has some KCSAN changes for the next
merge window. Although it seems git-merge figures out the resolution
for the conflict automatically.

Other than that,

Acked-by: Marco Elver <elver@...gle.com>

Thank you!

> diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
> index 27348029b2b8..c661484ee01f 100644
> --- a/scripts/Makefile.ubsan
> +++ b/scripts/Makefile.ubsan
> @@ -1,4 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0
> +
> +export CFLAGS_UBSAN :=
> +
>  ifdef CONFIG_UBSAN_ALIGNMENT
>        CFLAGS_UBSAN += $(call cc-option, -fsanitize=alignment)
>  endif
> --
> 2.25.1
>