linux-kernel - Re: [PATCH v6 3/5] samples: ftrace: Save required argument registers in sample trampolines

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Date:   Wed, 5 Apr 2023 16:40:24 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Florent Revest <revest@...omium.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org,
        catalin.marinas@....com, will@...nel.org, mhiramat@...nel.org,
        mark.rutland@....com, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kpsingh@...nel.org, jolsa@...nel.org,
        xukuohai@...weicloud.com, lihuafei1@...wei.com
Subject: Re: [PATCH v6 3/5] samples: ftrace: Save required argument
 registers in sample trampolines

On Wed,  5 Apr 2023 20:02:48 +0200
Florent Revest <revest@...omium.org> wrote:

> The ftrace-direct-too sample traces the handle_mm_fault function whose
> signature changed since the introduction of the sample. Since:
> commit bce617edecad ("mm: do page fault accounting in handle_mm_fault")
> handle_mm_fault now has 4 arguments. Therefore, the sample trampoline
> should save 4 argument registers.
> 
> s390 saves all argument registers already so it does not need a change
> but x86_64 needs an extra push and pop.
> 
> This also evolves the signature of the tracing function to make it
> mirror the signature of the traced function.
>

Should probably add:

Cc: stable@...r.kernel.org
Fixes: bce617edecad ("mm: do page fault accounting in handle_mm_fault")

Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>

-- Steve