linux-kernel - Re: [PATCH v2 3/4] tracing/kprobes: Don't pass addr=ip to perf_trace_buf

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Date:	Mon, 1 Jul 2013 21:45:55 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] tracing/kprobes: Don't pass addr=ip to
	perf_trace_buf_submit()

On 07/01, Steven Rostedt wrote:
>
> On Thu, 2013-06-20 at 19:38 +0200, Oleg Nesterov wrote:
> > kprobe_perf_func() and kretprobe_perf_func() pass addr=ip to
> > perf_trace_buf_submit() for no reason.
> >
> > This sets perf_sample_data->addr for PERF_SAMPLE_ADDR, we already
> > have perf_sample_data->ip initialized if PERF_SAMPLE_IP.
>
> This change log is confusing. I have no idea what this is trying to fix.
> Can you explain what is the issue here and what this change fixes.

Sorry for confusion, this fixes nothing.

Just there is no reason to pass "addr = kp.addr", we report it in entry.

Note also that kprobes is the last user perf_trace_buf_submit(addr != 0),
perhaps we can kill this arg and __perf_addr().

See also 32520b2c6 "Don't pass addr=ip to perf_trace_buf_submit()".

> Thanks,
> 
> -- Steve
> 
> > 
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> > ---
> >  kernel/trace/trace_kprobe.c |    6 ++----
> >  1 files changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index 3432652..141c682 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -1163,8 +1163,7 @@ kprobe_perf_func(struct trace_probe *tp, struct pt_regs *regs)
> >  	entry->ip = (unsigned long)tp->rp.kp.addr;
> >  	memset(&entry[1], 0, dsize);
> >  	store_trace_args(sizeof(*entry), tp, regs, (u8 *)&entry[1], dsize);
> > -	perf_trace_buf_submit(entry, size, rctx,
> > -					entry->ip, 1, regs, head, NULL);
> > +	perf_trace_buf_submit(entry, size, rctx, 0, 1, regs, head, NULL);
> >  }
> >  
> >  /* Kretprobe profile handler */
> > @@ -1197,8 +1196,7 @@ kretprobe_perf_func(struct trace_probe *tp, struct kretprobe_instance *ri,
> >  	entry->func = (unsigned long)tp->rp.kp.addr;
> >  	entry->ret_ip = (unsigned long)ri->ret_addr;
> >  	store_trace_args(sizeof(*entry), tp, regs, (u8 *)&entry[1], dsize);
> > -	perf_trace_buf_submit(entry, size, rctx,
> > -					entry->ret_ip, 1, regs, head, NULL);
> > +	perf_trace_buf_submit(entry, size, rctx, 0, 1, regs, head, NULL);
> >  }
> >  #endif	/* CONFIG_PERF_EVENTS */
> >  
> 
> 

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