linux-kernel - Re: [RFC PATCH -tip 1/9] ftrace: Add pt

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Date:	Fri, 01 Jun 2012 22:07:57 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [RFC PATCH -tip  1/9] ftrace: Add pt_regs acceptable trace
 callback

On Tue, 2012-05-29 at 21:48 +0900, Masami Hiramatsu wrote:

>  struct ftrace_ops {
> -	ftrace_func_t			func;
> +	union {
> +		ftrace_func_t			func;
> +		ftrace_regs_func_t		regs_func;
> +	};
>  	struct ftrace_ops		*next;
>  	unsigned long			flags;
>  	int __percpu			*disabled;
> @@ -164,6 +182,7 @@ static inline int ftrace_function_local_disabled(struct ftrace_ops *ops)
>  }

[..]

>  
>  static struct ftrace_ops global_ops = {
> -	.func			= ftrace_stub,
> +	.regs_func		= ftrace_regs_stub,
>  	.notrace_hash		= EMPTY_HASH,
>  	.filter_hash		= EMPTY_HASH,
> +	.flags			= FTRACE_OPS_FL_SAVE_REGS,
>  };
>  
>  static DEFINE_MUTEX(ftrace_regex_lock);
> @@ -3911,7 +3924,8 @@ void __init ftrace_init(void)
>  #else
>  
>  static struct ftrace_ops global_ops = {
> -	.func			= ftrace_stub,
> +	.regs_func		= ftrace_regs_stub,
> +	.flags			= FTRACE_OPS_FL_SAVE_REGS,
>  };
>  

Ug, this wont compile with some versions of gcc :-(

The one I stumbled on is gcc 4.5.1 (which I test builds against 4.5.1
and 4.6.0). Then I saw this BZ:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676

This can't be a union :-(  Then we can not initialize it.

I may go with my old approach and just change all callers to have a regs
parameter.

-- Steve


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