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

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Date: Fri, 24 May 2024 10:37:54 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.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 Thu, 23 May 2024 19:14:59 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> 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.

But what about rbx and r1*? Only regs->cs should be care for pt_regs?
Or, did you mean "the ftrace_regs is valid"?

> And x86_32 does support ftrace_regs, it just doesn't support
> having a subset of it.

Oh, thanks. I'll update the comment about x86_32.

Thank you,

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


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>