linux-kernel - Re: [PATCH v2 3/3] Kconfig: add ARCH_WANTS_NO_INSTR+CC_HAS_NO_PROFILE_FN

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Message-ID: <YNGQhgKd9Ruti5qZ@hirez.programming.kicks-ass.net>
Date:   Tue, 22 Jun 2021 09:25:58 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>, Bill Wendling <wcw@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        x86@...nel.org, Borislav Petkov <bp@...en8.de>,
        Martin Liska <mliska@...e.cz>, Marco Elver <elver@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Fangrui Song <maskray@...gle.com>, linux-doc@...r.kernel.org,
        linux-kbuild@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
        johannes.berg@...el.com, linux-toolchains@...r.kernel.org,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-s390@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v2 3/3] Kconfig: add
 ARCH_WANTS_NO_INSTR+CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO

On Mon, Jun 21, 2021 at 04:18:22PM -0700, Nick Desaulniers wrote:
> We don't want compiler instrumentation to touch noinstr functions, which
> are annotated with the no_profile_instrument_function function
> attribute. Add a Kconfig test for this and make PGO and GCOV depend on
> it.
> 
> If an architecture is using noinstr, it should denote that via this
> Kconfig value. That makes Kconfigs that depend on noinstr able to
> express dependencies in an architecturally agnostic way.
> 
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: Peter Oberparleiter <oberpar@...ux.ibm.com>
> Link: https://lore.kernel.org/lkml/YMTn9yjuemKFLbws@hirez.programming.kicks-ass.net/
> Link: https://lore.kernel.org/lkml/YMcssV%2Fn5IBGv4f0@hirez.programming.kicks-ass.net/
> Suggested-by: Nathan Chancellor <nathan@...nel.org>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
> Changes V1 -> V2:
> * Add ARCH_WANTS_NO_INSTR
> * Change depdendencies to be !ARCH_WANTS_NO_INSTR || CC_HAS_NO_PROFILE_FN_ATTR
>   rather than list architectures explicitly, as per Nathan.
> * s/no_profile/no_profile_instrument_function/
> 
>  arch/Kconfig        | 7 +++++++
>  arch/arm64/Kconfig  | 1 +
>  arch/s390/Kconfig   | 1 +
>  arch/x86/Kconfig    | 1 +
>  init/Kconfig        | 3 +++
>  kernel/gcov/Kconfig | 1 +
>  kernel/pgo/Kconfig  | 3 ++-
>  7 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 2b4109b0edee..2113c6b3b801 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -285,6 +285,13 @@ config ARCH_THREAD_STACK_ALLOCATOR
>  config ARCH_WANTS_DYNAMIC_TASK_STRUCT
>  	bool
>  
> +config ARCH_WANTS_NO_INSTR
> +	bool
> +	help
> +	  An architecure should select this if the noinstr macro is being used on
> +	  functions to denote that the toolchain should avoid instrumenting such
> +	  functions and is required for correctness.
> +
>  config ARCH_32BIT_OFF_T
>  	bool
>  	depends on !64BIT

There's also CC_HAS_WORKING_NOSANITIZE_ADDRESS in lib/Kconfig.kasan that
might want to be hooked into this, but that can be done separately I
suppose.