linux-kernel - Re: [PATCH 15/16] tracing: Add fields format definition for syscall events

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Message-ID: <20090819173734.GG4972@nowhere>
Date:	Wed, 19 Aug 2009 19:37:35 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Jiaying Zhang <jiayingz@...gle.com>,
	Martin Bligh <mbligh@...gle.com>,
	Li Zefan <lizf@...fujitsu.com>, Jason Baron <jbaron@...hat.com>
Subject: Re: [PATCH 15/16] tracing: Add fields format definition for
	syscall events

On Wed, Aug 19, 2009 at 01:12:48PM -0400, Masami Hiramatsu wrote:
> Frederic Weisbecker wrote:
> > Define the format of the syscall trace fields to parse the binary
> > values from a raw trace using the syscall events "format" file.
> > 
> > This is defined dynamically using the syscalls metadata.
> > It prepares the export of syscall event raw records to perf
> > counters.
> > 
> > Example:
> > 
> > $ cat /debug/tracing/events/syscalls/sys_enter_sched_getparam/format
> > name: sys_enter_sched_getparam
> > ID: 39
> > format:
> > 	field:unsigned short common_type;	offset:0;	size:2;
> > 	field:unsigned char common_flags;	offset:2;	size:1;
> > 	field:unsigned char common_preempt_count;	offset:3;	size:1;
> > 	field:int common_pid;	offset:4;	size:4;
> > 	field:int common_tgid;	offset:8;	size:4;
> > 
> > 	field:pid_t pid;	offset:12;	size:8;
> > 	field:struct sched_param * param;	offset:20;	size:8;
> > 
> > print fmt: "pid: 0x%08lx, param: 0x%08lx", ((unsigned long)(REC->pid)), ((unsigned long)(REC->param))
> 
> Hi Frederic,
> 
> I've found that the formats of some syscall events were too big.
> 
> ---
> $ for i in sys_enter* ;do grep name $i/format > /dev/null || echo $i has broken format. ; done sys_enter_getegid has broken format.
> sys_enter_geteuid has broken format.
> sys_enter_getgid has broken format.
> sys_enter_getpgrp has broken format.
> sys_enter_getpid has broken format.
> sys_enter_getppid has broken format.
> sys_enter_gettid has broken format.
> sys_enter_getuid has broken format.
> sys_enter_inotify_init has broken format.
> sys_enter_munlockall has broken format.
> sys_enter_pause has broken format.
> sys_enter_restart_syscall has broken format.
> sys_enter_sched_yield has broken format.
> sys_enter_setsid has broken format.
> sys_enter_sync has broken format.
> sys_enter_vhangup has broken format.
> 
> $ cat sys_enter_getegid/format
> FORMAT TOO BIG
> ---
> 
> And it causes an error on ./perf trace.
> 
> ---
> $ ./perf record -R -e syscalls:sys_enter_read -a -f  cat libperf.a > /dev/null
> 
> $ ./perf trace
>   Fatal: Error: expected 'name' but read 'FORMAT'
> version = 0.5
> ---
> 
> Thank you,


Yeah, I have yet to fix this, that because syscalls that have no parameters
raise a small bug in the return value of trace_seq_printf() while printing
their format, returning 0 as if the buffer was full and lost some bits.

However, It's possible that the last patches from Li fix this, since he did
a total/better refactoring of the format definition for syscall events.

I'll check this,
Thanks!

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