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

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Message-Id: <20150107153006.60ed354e3458f402e6819b9e@linux-foundation.org>
Date:	Wed, 7 Jan 2015 15:30:06 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jiri Kosina <jkosina@...e.cz>
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 Thu, 8 Jan 2015 00:01:02 +0100 (CET) Jiri Kosina <jkosina@...e.cz> wrote:

> 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.

um, what's so special about this patchset that it gets to be the first
code in the history of the kernel which breaks allmodconfig?

Please find a way to fix it.  Copying CONFIG_CC_STACKPROTECTOR is one way.

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