linux-kernel - Re: [PATCH v10 03/36] x86: tracing: Add ftrace

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Date: Thu, 23 May 2024 19:14:59 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Florent Revest
 <revest@...omium.org>, linux-trace-kernel@...r.kernel.org, LKML
 <linux-kernel@...r.kernel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,
 bpf <bpf@...r.kernel.org>, Sven Schnelle <svens@...ux.ibm.com>, Alexei
 Starovoitov <ast@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Arnaldo
 Carvalho de Melo <acme@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Alan Maguire <alan.maguire@...cle.com>, Mark Rutland
 <mark.rutland@....com>, Peter Zijlstra <peterz@...radead.org>, Thomas
 Gleixner <tglx@...utronix.de>, Guo Ren <guoren@...nel.org>
Subject: Re: [PATCH v10 03/36] x86: tracing: Add ftrace_regs definition in
 the header

On Tue,  7 May 2024 23:08:35 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> Add ftrace_regs definition for x86_64 in the ftrace header to
> clarify what register will be accessible from ftrace_regs.
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> ---
>  Changes in v3:
>   - Add rip to be saved.
>  Changes in v2:
>   - Newly added.
> ---
>  arch/x86/include/asm/ftrace.h |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> index cf88cc8cc74d..c88bf47f46da 100644
> --- a/arch/x86/include/asm/ftrace.h
> +++ b/arch/x86/include/asm/ftrace.h
> @@ -36,6 +36,12 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
>  
>  #ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
>  struct ftrace_regs {
> +	/*
> +	 * On the x86_64, the ftrace_regs saves;
> +	 * rax, rcx, rdx, rdi, rsi, r8, r9, rbp, rip and rsp.
> +	 * Also orig_ax is used for passing direct trampoline address.
> +	 * x86_32 doesn't support ftrace_regs.

Should add a comment that if fregs->regs.cs is set, then all of the pt_regs
is valid. And x86_32 does support ftrace_regs, it just doesn't support
having a subset of it.

-- Steve


> +	 */
>  	struct pt_regs		regs;
>  };
>