linux-kernel - Re: [PATCH] Documentation/ABI: Document the non-ABI status of Kconfig and symbols

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Date:	Thu, 24 Oct 2013 10:08:30 +0100
From:	Josh Triplett <josh@...htriplett.org>
To:	Richard Weinberger <richard.weinberger@...il.com>
Cc:	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rob Landley <rob@...dley.net>, Tao Ma <boyu.mt@...bao.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] Documentation/ABI: Document the non-ABI status of
 Kconfig and symbols

On Thu, Oct 24, 2013 at 10:57:11AM +0200, Richard Weinberger wrote:
> On Thu, Oct 24, 2013 at 10:41 AM, Josh Triplett <josh@...htriplett.org> wrote:
> > Discussion at Kernel Summit made it clear that the presence or absence
> > of specific Kconfig symbols are not considered ABI, and that no
> > userspace (or bootloader, etc) should rely on them.
> >
> > In addition, kernel-internal symbols are well established as non-ABI,
> > per Documentation/stable_api_nonsense.txt.
> >
> > Document both of these in Documentation/ABI/README, in a new section for
> > notable bits of non-ABI.
> >
> > Signed-off-by: Josh Triplett <josh@...htriplett.org>
> > ---
> >  Documentation/ABI/README | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/Documentation/ABI/README b/Documentation/ABI/README
> > index 1006982..1fafc4b 100644
> > --- a/Documentation/ABI/README
> > +++ b/Documentation/ABI/README
> > @@ -72,3 +72,16 @@ kernel tree without going through the obsolete state first.
> >
> >  It's up to the developer to place their interfaces in the category they
> >  wish for it to start out in.
> > +
> > +
> > +Notable bits of non-ABI, which should not under any circumstances be considered
> > +stable:
> > +
> > +- Kconfig.  Userspace should not rely on the presence or absence of any
> > +  particular Kconfig symbol, in /proc/config.gz, in the copy of .config
> > +  commonly installed to /boot, or in any invocation of the kernel build
> > +  process.
> > +
> > +- Kernel-internal symbols.  Do not rely on the presence, absence, location, or
> > +  type of any kernel symbol, either in System.map files or the kernel binary
> > +  itself.  See Documentation/stable_api_nonsense.txt.
> 
> And what about the kernel make "interface", is it considered also as non-ABI?
> 
> E.g.
> Before ffee0de (x86: Default to ARCH=x86 to avoid overriding CONFIG_64BIT)
> "make defconfig ARCH=x86" produced a i386 defconfig. Now it produces a
> x86_64 defconfig.
> I'm sure some build scripted failed badly.

I seriously considered including that, but I could imagine that some
parts of that interface might be considered more stable than others (the
names of targets, for instance), and I wanted to stick to completely
uncontroversial items.  If there's consensus that part or all of the
invocation of "make" to build the kernel is non-ABI, we can easily
enough add that to the non-ABI list, but let's start with Kconfig and
symbols.

- Josh Triplett
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