linux-kernel - Re: [RFC PATCH 0/2] libtraceevent/perf: Add support for trace-cmd plugins

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Date:	Tue, 19 Jun 2012 09:45:40 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	rostedt@...dmis.org, acme@...stprotocols.net,
	linux-kernel@...r.kernel.org, weisbec@...il.com,
	namhyung.kim@....com, mingo@...nel.org, peterz@...radead.org
Subject: Re: [RFC PATCH 0/2] libtraceevent/perf: Add support for trace-cmd plugins

On Mon, 18 Jun 2012 08:38:20 -0600, David Ahern wrote:
> Hi Namhyung:
>

Hi David,


> On 6/18/12 2:35 AM, Namhyung Kim wrote:
>> And for this particular case in patch 2/2, it seems that format of the
>> kvm_emulate_insn event is broken already and should be fixed anyway.
>> Further improvement in this area can be addressed in perf kvm or other
>> users if needed.
>
> kvm tracepoints are fine; perf just doesn't handle their (advanced)
> formatting.
>

Yeah, I think it's a libtraceevent's issue, not perf's. Please see
below:

TRACE_EVENT(kvm_emulate_insn,
        ...
	TP_printk("%x:%llx:%s (%s)%s",
		  __entry->csbase, __entry->rip,
		  __print_insn(__entry->insn, __entry->len),
		  __print_symbolic(__entry->flags,
				   kvm_trace_symbol_emul_flags),
		  __entry->failed ? " failed" : ""
		)
	);

And __print_insn is defined as:

#define __print_insn(insn, ilen) ({		                 \
	int i;							 \
	const char *ret = p->buffer + p->len;			 \
								 \
	for (i = 0; i < ilen; ++i)				 \
		trace_seq_printf(p, " %02x", insn[i]);		 \
	trace_seq_printf(p, "%c", 0);				 \
	ret;							 \
	})

The parse error is occurred at the beginning of the compound statment:

  Warning: bad op token {
  Warning: failed to read event print fmt for kvm_emulate_insn

I don't think we can handle this kind of compound statments easily. So I
just said it *seems* broken. :) Btw, calling trace_seq_printf() here also
looks like a problem and I have no idea where the 'p' came from.

Thanks,
Namhyung


> Note that I am referring to kvm:* tracepoints, not perf-kvm which has
> its own issues that need to be fixed.
>
> David
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