linux-kernel - Re: livepatching tree for linux-next

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Message-ID: <alpine.LNX.2.00.1501072346400.15299@pobox.suse.cz>
Date:	Thu, 8 Jan 2015 00:01:02 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	linux-next@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: livepatching tree for linux-next

On Wed, 7 Jan 2015, Andrew Morton wrote:

> > OK, I have added this from today
> 
> My x86_64 allmodconfig broke.
> 
> In file included from include/linux/livepatch.h:29,
>                  from kernel/livepatch/core.c:30:
> ./arch/x86/include/asm/livepatch.h:29:2: error: #error Your compiler must support -mfentry for live patching to work

[ adding Steven and Masami to CC, as this in some sense is related in 
  both to ftrace regs caller, and to IPMODIFY users in general ]

Well, if your gcc is too old (which is a fact detemined during build time, 
so there is no way to express this in Kconfig language in form of 
dependencies), we have to introduce build-time failure, as there is no way 
for this to work on compilers that don't support fentry on x86_64.

The only remaining option is to let the code build, pretend that 
everything is working, but do something like

#ifndef CC_USING_FENTRY
	printk("The compiler you used to compile your kernel was ancient "
		"there is no way for you to make use of this feature\n");
	return -EINVAL;
#endif

or so ... which I personally detest even more.

-- 
Jiri Kosina
SUSE Labs
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