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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Uwe Kleine-Konig <u.kleine-koenig@pengutronix.de>
Subject: Re: [PATCH] make CALLER_ADDRx overwriteable
Cc: kosaki.motohiro@jp.fujitsu.com, linux-kernel@vger.kernel.org,
       Steven Rostedt <rostedt@goodmis.org>,
       Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>
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Date: Fri, 27 Feb 2009 16:32:45 +0900 (JST)
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> The current definition of CALLER_ADDRx isn't suitable for all platforms.
> E.g. for ARM __builtin_return_address(N) doesn't work for N > 0 and
> AFAIK for powerpc there are no frame pointers needed to have a working
> __builtin_return_address.  This patch allows defining the CALLER_ADDRx
> macros in <asm/ftrace.h> and let these take precedence.
> 
> Because now <asm/ftrace.h> is included unconditionally in
> <linux/ftrace.h> all archs that don't already had this include get an
> empty one for free.

AFAIK, ia64 also doesn't work for N > 0.
thanks, good patch.



> -#ifdef CONFIG_FRAME_POINTER
> -/* TODO: need to fix this for ARM */
> -# define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
> -# define CALLER_ADDR1 ((unsigned long)__builtin_return_address(1))
> -# define CALLER_ADDR2 ((unsigned long)__builtin_return_address(2))
> -# define CALLER_ADDR3 ((unsigned long)__builtin_return_address(3))
> -# define CALLER_ADDR4 ((unsigned long)__builtin_return_address(4))
> -# define CALLER_ADDR5 ((unsigned long)__builtin_return_address(5))
> -# define CALLER_ADDR6 ((unsigned long)__builtin_return_address(6))
> -#else
> -# define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
> -# define CALLER_ADDR1 0UL
> -# define CALLER_ADDR2 0UL
> -# define CALLER_ADDR3 0UL
> -# define CALLER_ADDR4 0UL
> -# define CALLER_ADDR5 0UL
> -# define CALLER_ADDR6 0UL
> -#endif
> +#ifndef CALLER_ADDR0

but I think this "#ifndef CALLER_ADDR0" don't explain developer intention at all.
ARCH_HAS_XXXXX macro is better?

I would like to hear another developer opinions.


> +# ifdef CONFIG_FRAME_POINTER
> +#  define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
> +#  define CALLER_ADDR1 ((unsigned long)__builtin_return_address(1))
> +#  define CALLER_ADDR2 ((unsigned long)__builtin_return_address(2))
> +#  define CALLER_ADDR3 ((unsigned long)__builtin_return_address(3))
> +#  define CALLER_ADDR4 ((unsigned long)__builtin_return_address(4))
> +#  define CALLER_ADDR5 ((unsigned long)__builtin_return_address(5))
> +#  define CALLER_ADDR6 ((unsigned long)__builtin_return_address(6))
> +# else
> +#  define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
> +#  define CALLER_ADDR1 0UL
> +#  define CALLER_ADDR2 0UL
> +#  define CALLER_ADDR3 0UL
> +#  define CALLER_ADDR4 0UL
> +#  define CALLER_ADDR5 0UL
> +#  define CALLER_ADDR6 0UL
> +# endif
> +#endif /* ifndef CALLER_ADDR0 */