linux-kernel - Re: [PATCH/RFC 2/3] ftrace: introduce nohotpatch function attribute

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Message-ID: <20150126093701.699763dc@gandalf.local.home>
Date:	Mon, 26 Jan 2015 09:37:01 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Masami Hiramatsu <maasami.hiramatsu.pt@...achi.com>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Jiri Kosina <jkosina@...e.cz>, Jiri Slaby <jslaby@...e.cz>,
	Andreas Krebbel <krebbel@...ux.vnet.ibm.com>,
	Dominik Vogt <vogt@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC 2/3] ftrace: introduce nohotpatch function attribute

On Mon, 26 Jan 2015 13:54:53 +0100
Heiko Carstens <heiko.carstens@...ibm.com> wrote:

> gcc supports an s390 specific function attribute called "hotpatch".
> It can be used to specify the number of halfwords that shall be added before
> and after a function that shall be filled with nops for runtime patching.
> 
> s390 will use the hotpatch attribute for function tracing, therefore
> introduce a nohotpatch define, depending on CC_USING_HOTPATCH, and add it
> to the existing notrace define.

Are the two mutually exclusive? That is, can you have -pg and hotpatch
together? Reason why I ask is, if you have either -pg or hotpatch, then
we only need "no_instrument_function" or "hotpatch" in the notrace
define, not both. But I could be wrong.

-- Steve

> 
> Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
> ---
>  include/linux/compiler.h | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index b4fd7013c9f4..b4ab98e0e10b 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -54,7 +54,13 @@ extern void __chk_io_ptr(const volatile void __iomem *);
>  #include <linux/compiler-gcc.h>
>  #endif
>  
> -#define notrace __attribute__((no_instrument_function))
> +#ifdef CC_USING_HOTPATCH
> +#define nohotpatch __attribute__((hotpatch(0,0)))
> +#else
> +#define nohotpatch
> +#endif
> +
> +#define notrace __attribute__((no_instrument_function)) nohotpatch
>  
>  /* Intel compiler defines __GNUC__. So we will overwrite implementations
>   * coming from above header files here

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