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Date: Tue, 26 Jan 2016 13:48:53 +0100
From: Petr Mladek <pmladek@suse.com>
To: Miroslav Benes <mbenes@suse.cz>
Cc: Torsten Duwe <duwe@lst.de>, Steven Rostedt <rostedt@goodmis.org>,
 Michael Ellerman <mpe@ellerman.id.au>,
 Jiri Kosina <jkosina@suse.cz>, linuxppc-dev@lists.ozlabs.org,
 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
 live-patching@vger.kernel.org
Subject: Re: [PATCH v6 8/9] Implement kernel live patching for ppc64le (ABIv2)
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On Tue 2016-01-26 11:50:25, Miroslav Benes wrote:
> 
> [ added Petr to CC list ]
> 
> On Mon, 25 Jan 2016, Torsten Duwe wrote:
> 
> >   * create the appropriate files+functions
> >     arch/powerpc/include/asm/livepatch.h
> >         klp_check_compiler_support,
> >         klp_arch_set_pc
> >     arch/powerpc/kernel/livepatch.c with a stub for
> >         klp_write_module_reloc
> >     This is architecture-independent work in progress.
> >   * introduce a fixup in arch/powerpc/kernel/entry_64.S
> >     for local calls that are becoming global due to live patching.
> >     And of course do the main KLP thing: return to a maybe different
> >     address, possibly altered by the live patching ftrace op.
> > 
> > Signed-off-by: Torsten Duwe <duwe@suse.de>
> 
> Hi,
> 
> I have a few questions...
> 
> 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?
> 
> 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 
> change Petr's patch to make it more general and to be able to cope with 
> different prologues. This is unfortunate. Either way, please mention it 
> somewhere in a changelog.

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.

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.


Best Regards,
Petr