linux-kernel - Re: [PATCH] kasan: remove hwasan-kernel-mem-intrinsic-prefix=1 for clang-14

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Message-Id: <24ebf857-b70d-4d94-8870-e41b91649dd1@app.fastmail.com>
Date:   Fri, 14 Apr 2023 20:53:49 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Nathan Chancellor" <nathan@...nel.org>,
        "Arnd Bergmann" <arnd@...nel.org>
Cc:     "Andrey Ryabinin" <ryabinin.a.a@...il.com>,
        "Masahiro Yamada" <masahiroy@...nel.org>,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Marco Elver" <elver@...gle.com>,
        "Nicolas Schier" <nicolas@...sle.eu>,
        "Alexander Potapenko" <glider@...gle.com>,
        "Andrey Konovalov" <andreyknvl@...il.com>,
        "Dmitry Vyukov" <dvyukov@...gle.com>,
        "Vincenzo Frascino" <vincenzo.frascino@....com>,
        "Tom Rix" <trix@...hat.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        "Peter Zijlstra" <peterz@...radead.org>,
        linux-kbuild@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] kasan: remove hwasan-kernel-mem-intrinsic-prefix=1 for clang-14

On Fri, Apr 14, 2023, at 18:26, Nathan Chancellor wrote:
> On Fri, Apr 14, 2023 at 10:29:27AM +0200, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@...db.de>
>> 
>> Unknown -mllvm options don't cause an error to be returned by clang, so
>> the cc-option helper adds the unknown hwasan-kernel-mem-intrinsic-prefix=1
>> flag to CFLAGS with compilers that are new enough for hwasan but too
>
> Hmmm, how did a change like commit 0e1aa5b62160 ("kcsan: Restrict
> supported compilers") work if cc-option does not work with unknown
> '-mllvm' flags (or did it)? That definitely seems like a problem, as I
> see a few different places where '-mllvm' options are used with
> cc-option. I guess I will leave that up to the sanitizer folks to
> comment on that further, one small comment below.

That one adds both "-fsanitize=thread" and "-mllvm
-tsan-distinguish-volatile=1". If the first one is missing in the
compiler, neither will be set. If only the second one fails, I assume
you'd get the same result I see with hwasan-kernel-mem-intrinsic-prefix=1.

>>  # Instrument memcpy/memset/memmove calls by using instrumented __hwasan_mem*().
>> +ifeq ($(call clang-min-version, 150000),y)
>>  CFLAGS_KASAN += $(call cc-param,hwasan-kernel-mem-intrinsic-prefix=1)
>> +endif
>> +ifeq ($(call gcc-min-version, 130000),y)
>> +CFLAGS_KASAN += $(call cc-param,hwasan-kernel-mem-intrinsic-prefix=1)
>> +endif
>
> I do not think you need to duplicate this block, I think
>
>   ifeq ($(call clang-min-version, 150000)$(call gcc-min-version, 130000),y)
>   CFLAGS_KASAN += $(call cc-param,hwasan-kernel-mem-intrinsic-prefix=1)
>   endif
>
> would work, as only one of those conditions can be true at a time.

Are you sure that clang-min-version evaluates to an empty string
rather than "n" or something else? I haven't found a documentation
that says anything about it other than it returning "y" if the condition
is true.

      Arnd