Re: [PATCH v2 3/3] Kconfig: add ARCH_WANTS_NO_INSTR+CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO

From: Peter Zijlstra <peterz@infradead.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Kees Cook <keescook@chromium.org>, Bill Wendling <wcw@google.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	Peter Oberparleiter <oberpar@linux.ibm.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
	Ard Biesheuvel <ardb@kernel.org>, Will Deacon <will@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
	x86@kernel.org, Borislav Petkov <bp@alien8.de>,
	Martin Liska <mliska@suse.cz>, Marco Elver <elver@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Fangrui Song <maskray@google.com>,
	linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org,
	Dmitry Vyukov <dvyukov@google.com>,
	johannes.berg@intel.com, linux-toolchains@vger.kernel.org,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	linux-s390@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	Catalin Marinas <catalin.marinas@arm.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
Date: Tue, 22 Jun 2021 09:25:58 +0200	[thread overview]
Message-ID: <YNGQhgKd9Ruti5qZ@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210621231822.2848305-4-ndesaulniers@google.com>

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@kernel.org>
> Cc: Peter Oberparleiter <oberpar@linux.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@kernel.org>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.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.