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Date: Thu, 27 Aug 2009 17:38:56 -0700
From: Josh Stone <jistone@redhat.com>
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To: Frederic Weisbecker <fweisbec@gmail.com>
CC: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Li Zefan <lizf@cn.fujitsu.com>, Steven Rostedt <srostedt@redhat.com>,
       Jason Baron <jbaron@redhat.com>
Subject: Re: [PATCH] tracing: Fix double CPP substitution in TRACE_EVENT_FN
References: <tip-97419875865859fd2403e66266c02ce028e2f5ab@git.kernel.org> <1251413406-6704-1-git-send-email-fweisbec@gmail.com>
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On 08/27/2009 03:50 PM, Frederic Weisbecker wrote:
> TRACE_EVENT_FN relays on TRACE_EVENT by reprocessing its parameters
> into the ftrace events CPP macro. This leads to a double substitution
> in some cases.
> 
> For example, a bad consequence is a format always prefixed by
> "%s, %s\n" for every TRACE_EVENT_FN based events.
> 
> Eg:
> 	cat /debug/tracing/events/syscalls/sys_enter/format
> 	[...]
> 	print fmt: "%s, %s\n", "\"NR %ld (%lx, %lx, %lx, %lx, %lx, %lx)\"",\
> 	"REC->id, REC->args[0], REC->args[1], REC->args[2], REC->args[3],\
> 	REC->args[4], REC->args[5]"
> 
> This creates a failure in post-processing tools such as perf trace or
> trace-cmd.

Fun - I didn't think about TP_printk and friends doing anything beside
passing their contents along.

> 
> Then drop this double substitution and replace it by a new __cpparg()
> macro that relays CPP arguments containing commas.

Looks good to me.

> 
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Josh Stone <jistone@redhat.com>
> Cc: Li Zefan <lizf@cn.fujitsu.com>
> Cc: Steven Rostedt <srostedt@redhat.com>
> Cc: Jason Baron <jbaron@redhat.com>

Reviewed-by: Josh Stone <jistone@redhat.com>