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

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Date: Fri, 24 May 2024 10:31:44 -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 Fri, 24 May 2024 10:37:54 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:
> > >  
> > >  #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"?

Yeah, on x86_64 ftrace_regs uses regs.cs to denote if it is valid or not:

static __always_inline struct pt_regs *
arch_ftrace_get_regs(struct ftrace_regs *fregs)
{
	/* Only when FL_SAVE_REGS is set, cs will be non zero */
	if (!fregs->regs.cs)
		return NULL;
	return &fregs->regs;
}


-- Steve