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Date:   Fri, 14 Apr 2023 20:53:49 +0200
From:   "Arnd Bergmann" <arnd@arndb.de>
To:     "Nathan Chancellor" <nathan@kernel.org>,
        "Arnd Bergmann" <arnd@kernel.org>
Cc:     "Andrey Ryabinin" <ryabinin.a.a@gmail.com>,
        "Masahiro Yamada" <masahiroy@kernel.org>,
        "Nick Desaulniers" <ndesaulniers@google.com>,
        "Marco Elver" <elver@google.com>,
        "Nicolas Schier" <nicolas@fjasle.eu>,
        "Alexander Potapenko" <glider@google.com>,
        "Andrey Konovalov" <andreyknvl@gmail.com>,
        "Dmitry Vyukov" <dvyukov@google.com>,
        "Vincenzo Frascino" <vincenzo.frascino@arm.com>,
        "Tom Rix" <trix@redhat.com>,
        "Andrew Morton" <akpm@linux-foundation.org>,
        "Michael Ellerman" <mpe@ellerman.id.au>,
        "Peter Zijlstra" <peterz@infradead.org>,
        linux-kbuild@vger.kernel.org, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH] kasan: remove hwasan-kernel-mem-intrinsic-prefix=1 for clang-14
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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@arndb.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