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

[Peter Zijlstra]

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@xxxxxxxxxx>
> Cc: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/YMTn9yjuemKFLbws@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> Link: https://lore.kernel.org/lkml/YMcssV%2Fn5IBGv4f0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> Suggested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> ---
> 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.