linux-kernel - Re: [RFC][PATCH 1/2] tracing/ftrace: syscall tracing infrastructure

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Date:	Mon, 9 Mar 2009 21:40:14 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	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>
Subject: Re: [RFC][PATCH 1/2] tracing/ftrace: syscall tracing infrastructure

On Sun, Mar 08, 2009 at 05:24:44PM +0100, Ingo Molnar wrote:
> 
> * Frederic Weisbecker <fweisbec@...il.com> wrote:
> 
> > +static const struct syscall_trace_entry syscall_trace_entries[] = {
> > +	/* For open, the first argument is a string, hence the given mask */
> > +	[SYSCALL_TRACE_OPEN]	= SYS_TRACE_ENTRY(open, 3, 0x1),
> > +	[SYSCALL_TRACE_CLOSE]	= SYS_TRACE_ENTRY(close, 1, 0),
> > +	[SYSCALL_TRACE_READ]	= SYS_TRACE_ENTRY(read, 3, 0),
> > +	[SYSCALL_TRACE_WRITE]	= SYS_TRACE_ENTRY(read, 3, 0),
> > +};
> 
> s/read/write in the last entry i guess.
> 
> But i think the whole concept of duplicating the syscall table 
> is the wrong way around.
> 
> Note that we dont have to build this information at all - in 
> 2.6.29-rc1 all syscalls got wrapper macros:
> 
>  SYSCALL_DEFINE1(nice, int, increment)
>  SYSCALL_DEFINE2(sched_setparam, pid_t, pid, struct sched_param __user *, param)
>  SYSCALL_DEFINE3(sched_setaffinity, pid_t, pid, unsigned int, len,
>                  unsigned long __user *, user_mask_ptr)
> 
> We also have the syscall table itself.
> 
> So what we can do: by changing the SYSCALL_DEFINEX() macros we 
> can emit the following information into a table:
> 
>   (syscall_fn_address, syscall_name_string, #of arguments, array 
>    of argument names and type sizeof()s)
> 
> then during bootup we can match up the sys_call_table[] to the 
> secondary table we built, so that we can order the secondary 
> table based on syscall NR. 99% of the syscalls will match up 
> just fine.
> 
> 	Ingo

Yes, I didn't know the SYSCALL_DEFINEx() macro until Peter told me.
That's indeed a much better way to proceed, I will look at all that.


Thanks!

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