linux-kernel - Re: [PATCH v8 8/8] livepatch: Detect offset for the ftrace location during build

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Date:	Tue, 16 Feb 2016 09:23:02 +0100
From:	Torsten Duwe <duwe@....de>
To:	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
Cc:	Petr Mladek <pmladek@...e.com>,
	Balbir Singh <bsingharora@...il.com>,
	Jessica Yu <jeyu@...hat.com>, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Jiri Kosina <jkosina@...e.cz>, live-patching@...r.kernel.org,
	Miroslav Benes <mbenes@...e.cz>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v8 8/8] livepatch: Detect offset for the ftrace
	location during build

On Tue, Feb 16, 2016 at 11:17:02AM +0530, Kamalesh Babulal wrote:
> * Petr Mladek <pmladek@...e.com> [2016-02-12 17:45:17]:
> >  int test(int a)
> >  {
> > +	printk("%d\n", a);
> >  	return ++a;
> >  }
> 
> Thanks. This workaround, helped to load sample livepatch module.

N.b.: if you try to livepatch/trace such a leaf function without
global dependencies, it will crash if that function got called with
a different TOC value. Hence this whole testing.

You may alternatively try my gcc patch ;-)

Another caveat is functions with stack arguments (>8 args, varargs).
My code needs special precautions then because of the return helper.

	Torsten