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

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Date:	Mon, 26 Jan 2015 16:03:19 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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, Jan 26, 2015 at 09:37:01AM -0500, Steven Rostedt wrote:
> 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.

Actually they should be mutually exclusive. I just merged them "just in case".

So something like this

#ifdef CC_USING_HOTPATCH
#define notrace __attribute__((hotpatch(0,0)))
#else
#define notrace __attribute__((no_instrument_function))
#endif

will work as well (just tested).

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