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From:   Marco Elver <elver@google.com>
Date:   Fri, 29 May 2020 16:56:09 +0200
Message-ID: <CANpmjNPr5MrwPFOW10pRkUgxwktXNiUweNj+pGJMunoZKi7Cdw@mail.gmail.com>
Subject: Re: [PATCH] kasan: fix clang compilation warning due to stack protector
To:     Andrey Konovalov <andreyknvl@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, Qian Cai <cai@lca.pw>
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On Thu, 28 May 2020 at 19:20, 'Andrey Konovalov' via kasan-dev
<kasan-dev@googlegroups.com> wrote:
>
> KASAN uses a single cc-option invocation to disable both conserve-stack
> and stack-protector flags. The former flag is not present in Clang, which
> causes cc-option to fail, and results in stack-protector being enabled.
>
> Fix by using separate cc-option calls for each flag. Also collect all
> flags in a variable to avoid calling cc-option multiple times for
> different files.
>
> Reported-by: Qian Cai <cai@lca.pw>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---

Thank you! I was about to send an almost identical patch, as I
encountered this when using clang.

Reviewed-by: Marco Elver <elver@google.com>

>  mm/kasan/Makefile | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
> index de3121848ddf..bf6f7b1f6b18 100644
> --- a/mm/kasan/Makefile
> +++ b/mm/kasan/Makefile
> @@ -15,14 +15,19 @@ CFLAGS_REMOVE_tags_report.o = $(CC_FLAGS_FTRACE)
>
>  # Function splitter causes unnecessary splits in __asan_load1/__asan_store1
>  # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
> -CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> -CFLAGS_generic.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> -CFLAGS_generic_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> -CFLAGS_init.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> -CFLAGS_quarantine.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> -CFLAGS_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> -CFLAGS_tags.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> -CFLAGS_tags_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
> +CC_FLAGS_KASAN_CONFLICT := $(call cc-option, -fno-conserve-stack)
> +CC_FLAGS_KASAN_CONFLICT += $(call cc-option, -fno-stack-protector)
> +# Disable branch tracing to avoid recursion.
> +CC_FLAGS_KASAN_CONFLICT += -DDISABLE_BRANCH_PROFILING

Note that maybe CC_FLAGS_KASAN_RUNTIME could be a better name, because
other flags added in future might not be conflict-related. But until
that future, it doesn't really matter.

> +CFLAGS_common.o := $(CC_FLAGS_KASAN_CONFLICT)
> +CFLAGS_generic.o := $(CC_FLAGS_KASAN_CONFLICT)
> +CFLAGS_generic_report.o := $(CC_FLAGS_KASAN_CONFLICT)
> +CFLAGS_init.o := $(CC_FLAGS_KASAN_CONFLICT)
> +CFLAGS_quarantine.o := $(CC_FLAGS_KASAN_CONFLICT)
> +CFLAGS_report.o := $(CC_FLAGS_KASAN_CONFLICT)
> +CFLAGS_tags.o := $(CC_FLAGS_KASAN_CONFLICT)
> +CFLAGS_tags_report.o := $(CC_FLAGS_KASAN_CONFLICT)
>
>  obj-$(CONFIG_KASAN) := common.o init.o report.o
>  obj-$(CONFIG_KASAN_GENERIC) += generic.o generic_report.o quarantine.o
> --
> 2.27.0.rc0.183.gde8f92d652-goog
>
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