linux-kernel - Re: [PATCH 2/2 v2] tracing/syscalls: support for syscalls tracing on x86-64

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Message-ID: <20090315160538.GE5105@nowhere>
Date:	Sun, 15 Mar 2009 17:05:40 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>, tglx@...utronix.de,
	Jason Baron <jbaron@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Jiaying Zhang <jiayingz@...gle.com>,
	Michael Rubin <mrubin@...gle.com>,
	Martin Bligh <mbligh@...gle.com>,
	Michael Davidson <md@...gle.com>
Subject: Re: [PATCH 2/2 v2] tracing/syscalls: support for syscalls tracing
	on x86-64

On Sun, Mar 15, 2009 at 06:30:18AM +0100, Ingo Molnar wrote:
> 
> * Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Fri, 13 Mar 2009 15:42:12 +0100 Frederic Weisbecker <fweisbec@...il.com> wrote:
> > 
> > > +static struct syscall_metadata *find_syscall_meta(unsigned long *syscall)
> > > +{
> > > +	struct syscall_metadata *start;
> > > +	struct syscall_metadata *stop;
> > > +	char str[KSYM_SYMBOL_LEN];
> > > +
> > > +
> > > +	start = (struct syscall_metadata *)__start_syscalls_metadata;
> > > +	stop = (struct syscall_metadata *)__stop_syscalls_metadata;
> > > +	kallsyms_lookup((unsigned long) syscall, NULL, NULL, NULL, str);
> > > +
> > > +	for ( ; start < stop; start++) {
> > > +		if (start->name && !strcmp(start->name, str))
> > > +			return start;
> > > +	}
> > > +	return NULL;
> > > +}
> > 
> > afacit this feature can be enabled when CONFIG_KALLSYMS=n.  
> > Does that make sense?
> 
> It does not make much sense - the function will return NULL and 
> we wont do any tracing. Frederic: FTRACE_SYSCALLS should either 
> select KALLSYMS in kernel/trace/Kconfig, like the STACK_TRACER 
> and FUNCTION_TRACER already does. Or perhaps, for really 
> puritane tracing, we should emit simplified, non-symbolic trace 
> data in the !KALLSYMS case.
> 
> 	Ingo

You're right. But it would be somewhat pointless to trace the syscalls
without their names.
I will make it select KALLSYMS, it seems to me a sane way to fix it.

Thanks.

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