linux-kernel - Re: [PATCH 2/4] ARM: add IPI tracepoints

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Date:	Fri, 18 Jul 2014 16:55:42 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Ingo Molnar <mingo@...hat.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH 2/4] ARM: add IPI tracepoints

On Fri, 18 Jul 2014, Steven Rostedt wrote:

> On Fri, 18 Jul 2014 01:18:53 -0400
> Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> 
>   
> > -#ifdef CONFIG_IRQ_WORK
> > -void arch_irq_work_raise(void)
> > -{
> > -	if (is_smp())
> > -		smp_cross_call(cpumask_of(smp_processor_id()), IPI_IRQ_WORK);
> > -}
> > +static const char *ipi_types[NR_IPI]
> > +#ifdef CONFIG_TRACING
> > +__tracepoint_string
> >  #endif
> 
> Oh, this is ugly. I should probably add a define when !CONFIG_TRACING
> is set. Something like:
> 
> #ifdef CONFIG_TRACING
> ...
> #else
> # define __tracepoint_string
> #endif
> 
> Such that users of __tracepoint_string don't need to add ugly ifdefs in
> the code.
> 
> If you want to add that to ftrace_event.h to this series, I'll ack it.

Here's the patch I have at the head of the series now, with the above
ugliness changed to an unconditional __tracepoint_string attribute.

From: Nicolas Pitre <nicolas.pitre@...aro.org>
Date: Fri, 18 Jul 2014 16:34:39 -0400
Subject: [PATCH] trace: don't refer __tracepoint_string to an undefined linker section

When CONFIG_TRACING is not set, the linker script doesn't specify any
__tracepoint_str section.  Let those __tracepoint_string marked strings
live in the default rodata section in that case.

Signed-off-by: Nicolas Pitre <nico@...aro.org>

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index cff3106ffe..d6346607e4 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -606,7 +606,11 @@ do {									\
 		static const char *___tp_str __tracepoint_string = str; \
 		___tp_str;						\
 	})
+#ifdef CONFIG_TRACING
 #define __tracepoint_string	__attribute__((section("__tracepoint_str")))
+#else
+#define __tracepoint_string
+#endif
 
 #ifdef CONFIG_PERF_EVENTS
 struct perf_event;
--
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