linux-kernel - Re: [PATCH v8 6/8] Implement kernel live patching for ppc64le (ABIv2)

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Date:	Thu, 11 Feb 2016 10:01:54 +0100 (CET)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Torsten Duwe <duwe@....de>
cc:	Michael Ellerman <mpe@...erman.id.au>,
	Jiri Kosina <jkosina@...e.cz>, Petr Mladek <pmladek@...e.com>,
	Jessica Yu <jeyu@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org
Subject: Re: [PATCH v8 6/8] Implement kernel live patching for ppc64le
 (ABIv2)

On Wed, 10 Feb 2016, Torsten Duwe wrote:

> diff --git a/arch/powerpc/include/asm/livepatch.h b/arch/powerpc/include/asm/livepatch.h
> new file mode 100644
> index 0000000..44e8a2d
> --- /dev/null
> +++ b/arch/powerpc/include/asm/livepatch.h
> @@ -0,0 +1,45 @@
> +/*
> + * livepatch.h - powerpc-specific Kernel Live Patching Core
> + *
> + * Copyright (C) 2015 SUSE
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +#ifndef _ASM_POWERPC64_LIVEPATCH_H
> +#define _ASM_POWERPC64_LIVEPATCH_H
> +
> +#include <linux/module.h>
> +#include <linux/ftrace.h>
> +
> +#ifdef CONFIG_LIVEPATCH
> +static inline int klp_check_compiler_support(void)
> +{
> +#if !defined(_CALL_ELF) || _CALL_ELF != 2 || !defined(CC_USING_MPROFILE_KERNEL)
> +	return 1;
> +#endif
> +	return 0;
> +}
> +
> +extern int klp_write_module_reloc(struct module *mod, unsigned long type,
> +				   unsigned long loc, unsigned long value);

It would be better to make this one static inline and move 'return 
-ENOSYS;' here. Thus there would be no arch/powerpc/kernel/livepatch.c. 
See s390 code for reference.

> +static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
> +{
> +	regs->nip = ip;
> +}
> +#else
> +#error Live patching support is disabled; check CONFIG_LIVEPATCH

Change the error to

#error Include linux/livepatch.h, not asm/livepatch.h

please. See 383bf44d1a8b ("livepatch: change the error message in 
asm/livepatch.h header files").

Thanks Torsten,
Miroslav