linux-kernel - Re: [PATCH v6 8/9] Implement kernel live patching for ppc64le (ABIv2)

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Message-ID: <20160126135621.GA28664@lst.de>
Date:	Tue, 26 Jan 2016 14:56:21 +0100
From:	Torsten Duwe <duwe@....de>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Miroslav Benes <mbenes@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Jiri Kosina <jkosina@...e.cz>, linuxppc-dev@...ts.ozlabs.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	live-patching@...r.kernel.org
Subject: Re: [PATCH v6 8/9] Implement kernel live patching for ppc64le
	(ABIv2)

On Tue, Jan 26, 2016 at 01:48:53PM +0100, Petr Mladek wrote:
> On Tue 2016-01-26 11:50:25, Miroslav Benes wrote:
> > 
> > We still need Petr's patch from [1] to make livepatch work, right? Could 
> > you, please, add it to this patch set to make it self-sufficient?

It's Petr's patch, I don't want to decide how to best tackle this, see below.
I think Michael is already aware that it is needed, too.

> > Second, what is the situation with mcount prologue between gcc < 6 and 
> > gcc-6? Are there only 12 bytes in gcc-6 prologue? If yes, we need to 

Precisely, it's commit e95d0248daced44 (in http://repo.or.cz/official-gcc.git)
or svn trunk change 222352 "No need for -mprofile-kernel to save LR to stack."
It's efficient, I like it.

> I am going to update the extra patch. There is an idea to detect the
> offset during build by scrips/recordmcount. This tool looks for the
> ftrace locations. The offset should always be a constant that depends
> on the used architecture, compiler, and compiler flags.

My first idea was to check for compiler version defines, but some vendors
are rumoured to patch their compilers ;-)

> The tool is called post build. We might need to pass the constant
> as a symbol added to the binary. The tool already adds some symbols.

That's even better.
Thanks!
	Torsten