linux-kernel - Re: [PATCH v7 23/36] function_graph: Add a new exit handler with parent_ip and ftrace

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Date: Sun, 18 Feb 2024 11:53:28 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, 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 v7 23/36] function_graph: Add a new exit handler with
 parent_ip and ftrace_regs

On Fri, 16 Feb 2024 17:51:08 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> > > @@ -798,10 +798,6 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
> > >  
> > >  	*index += FGRAPH_RET_INDEX;
> > >  	*ret = ret_stack->ret;
> > > -	trace->func = ret_stack->func;
> > > -	trace->calltime = ret_stack->calltime;
> > > -	trace->overrun = atomic_read(&current->trace_overrun);
> > > -	trace->depth = current->curr_ret_depth;
> > 
> > There's a lot of information stored in the trace structure. Why not pass
> > that to the new retregfunc?
> > 
> > Then you don't need to separate this code out.
> 
> Sorry, I couldn't catch what you meant, Would you mean to call
> ftrace_pop_return_trace() before calling retregfunc()?? because some of the
> information are found from ret_stack, which is poped from shadow stack.

Ah, sorry I got what you said. I think this `trace` is not usable for the new
interface. Most of the information is only used for the function-graph tracer.
For example, trace->calltime and trace->overrun, trace->depth are used only
for the function-graph tracer, but not for the other tracers.

But yeah, this idea is considerable. It also allows us to just update
entryfunc() and retfunc() to pass fgraph_regs and return address.

Thank you!

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