linux-kernel - Re: [PATCH] ftrace: Allow WITH_ARGS flavour of graph tracer with shadow call stack

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Message-ID: <Y5NI2TKtGbDKyt53@FVFF77S0Q05N>
Date:   Fri, 9 Dec 2022 14:40:25 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        will@...nel.org, rostedt@...dmis.org, samitolvanen@...gle.com,
        keescook@...omium.org, mhiramat@...nel.org
Subject: Re: [PATCH] ftrace: Allow WITH_ARGS flavour of graph tracer with
 shadow call stack

On Fri, Dec 09, 2022 at 03:34:02PM +0100, Ard Biesheuvel wrote:
> The recent switch on arm64 from DYNAMIC_FTRACE_WITH_REGS to
> DYNAMIC_FTRACE_WITH_ARGS failed to take into account that we currently
> require the former in order to allow the function graph tracer to be
> enabled in combination with shadow call stacks. This means that this is
> no longer permitted at all, in spite of the fact that either flavour of
> ftrace works perfectly fine in this combination.
> 
> Given that arm64 is the only arch that implements shadow call stacks in
> the first place, let's update the condition to just reflect the arm64
> change. When other architectures adopt shadow call stack support, this
> can be revisited if needed.
> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>

My bad; sorry about this, and thanks for the fix!

Acked-by: Mark Rutland <mark.rutland@....com>

We should probably also add:

Fixes: 26299b3f6ba26bfc ("ftrace: arm64: move from REGS to ARGS")

Mark.

> ---
>  arch/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 072a1b39e3afd0d1..683f365b5e31c856 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -635,7 +635,7 @@ config ARCH_SUPPORTS_SHADOW_CALL_STACK
>  config SHADOW_CALL_STACK
>  	bool "Shadow Call Stack"
>  	depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
> -	depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
> +	depends on DYNAMIC_FTRACE_WITH_ARGS || !FUNCTION_GRAPH_TRACER
>  	help
>  	  This option enables the compiler's Shadow Call Stack, which
>  	  uses a shadow stack to protect function return addresses from
> -- 
> 2.35.1
>