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

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Date:   Fri, 14 Apr 2023 09:26:05 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     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>, Arnd Bergmann <arnd@...db.de>,
        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 (Intel)" <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 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.

> old for this option. This causes a rather unreadable build failure:
> 
> fixdep: error opening file: scripts/mod/.empty.o.d: No such file or directory
> make[4]: *** [/home/arnd/arm-soc/scripts/Makefile.build:252: scripts/mod/empty.o] Error 2
> fixdep: error opening file: scripts/mod/.devicetable-offsets.s.d: No such file or directory
> make[4]: *** [/home/arnd/arm-soc/scripts/Makefile.build:114: scripts/mod/devicetable-offsets.s] Error 2
> 
> Add a version check to only allow this option with clang-15, gcc-13
> or later versions.
> 
> Fixes: 51287dcb00cc ("kasan: emit different calls for instrumentable memintrinsics")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> There is probably a better way to do this than to add version checks,
> but I could not figure it out.
> ---
>  scripts/Makefile.kasan | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
> index c186110ffa20..2cea0592e343 100644
> --- a/scripts/Makefile.kasan
> +++ b/scripts/Makefile.kasan
> @@ -69,7 +69,12 @@ CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
>  		$(instrumentation_flags)
>  
>  # Instrument memcpy/memset/memmove calls by using instrumented __hwasan_mem*().
> +ifeq ($(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.

Cheers,
Nathan