linux-kernel - Re: [PATCH] tracing: Fix to use unused attribute

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Date:	Thu, 29 Oct 2009 08:57:35 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Li Zefan <lizf@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: Fix to use unused attribute


* Li Zefan <lizf@...fujitsu.com> wrote:

> ____ftrace_check_##name() is used for compile-time check
> on F_printk() only, so it should be marked as __unused
> instead of __used.
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
> 
> I'm thinking about introducing __always_unused, comparing
> to __maybe_unused.
> 
> ---
>  kernel/trace/trace_export.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_export.c b/kernel/trace/trace_export.c
> index 934d81f..85309fc 100644
> --- a/kernel/trace/trace_export.c
> +++ b/kernel/trace/trace_export.c
> @@ -48,11 +48,12 @@
>  struct ____ftrace_##name {					\
>  	tstruct							\
>  };								\
> -static void __used ____ftrace_check_##name(void)		\
> +static void __attribute__((unused))				\
> +____ftrace_check_##name(void)					\
>  {								\
>  	struct ____ftrace_##name *__entry = NULL;		\
>  								\
> -	/* force cmpile-time check on F_printk() */		\
> +	/* force compile-time check on F_printk() */		\
>  	printk(print);						\
>  }

Hm, open-coding __attribute__()'s is not good.

These tags are somewhat of a mess:

 #if __GNUC_MINOR__ >= 3
 # define __used                 __attribute__((__used__))
 #else
 # define __used                 __attribute__((__unused__))
 #endif

I've Cc:-ed Linus and Andrew, to solicite feedback on __always_unused. I 
think we should add it.

	Ingo
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