linux-kernel - Re: 2.6.24-rc1-82798a1 compile failure (x86

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Date:	Sun, 4 Nov 2007 11:04:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Adrian Bunk <bunk@...nel.org>
Cc:	Sam Ravnborg <sam@...nborg.org>,
	Thomas Bächler <thomas@...hlinux.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: 2.6.24-rc1-82798a1 compile failure (x86_64)


* Adrian Bunk <bunk@...nel.org> wrote:

> On Sat, Nov 03, 2007 at 01:11:49PM +0100, Sam Ravnborg wrote:
> > On Sat, Nov 03, 2007 at 11:04:36AM +0100, Thomas Bächler wrote:
> > > Thomas Bächler schrieb:
> > > > 
> > > > I just remembered, a friend of mine got it to compile with the exact
> > > > same toolchain, but with a different configuration (which I don't have).
> > > > He used a snapshot tarball from yesterday though, not the git tree.
> > > > 
> > > 
> > > I found the problem and eliminated it. While this is my own fault, it is
> > > still a bug in either the kernel or the build system: I had CFLAGS set
> > > to "-Wall -O3 -march=native -pipe". I always thought the kernel would
> > > ignore those and set its own CFLAGS, but I was wrong. Either the -O3 or
> > > the -march=native break the build process on gcc 4.2.2.
> > > 
> > The kernel will now honour the users CFLAGS setting as you just discovered.
> > The flags will be appended to the flags specified by the kernel.
> >...
> 
> I think this should be changed:
> 
> I also have CFLAGS set on some computers in my environments since for 
> packages using GNU autoconf that's the correct way to set the compiler 
> flags.
> 
> The kernel already sets all flags correctly, and a user wanting to 
> change the flags for the kernel is an exception with very special 
> needs (I'd even claim so special that he could simply edit the 
> Makefile...).
> 
> Using the *FLAGS automatically in the kernel doesn't sound right, can 
> we prefix all environment variables the kernel honours with KERNEL_ ?

this _must_ be changed before v2.6.24 is released. Thomas Bächler, 
Thomas Gleixner and me already wasted hours on this problem, and these 
kinds of issues will reoccur again and again - in perhaps even more 
spurious ways.

Picking up randon environment details during build reduces 
reproducability (i couldnt reproduce the problem using the exact same 
toolchain) and might break various existing setups and distro builds as 
well.

At minimum the extra CFLAGS needs to be put into the .config - but 
that's not a too nice solution either. How about just adding an 
extra-CFLAGS option to .config and perhaps a 'make configpickupCFLAGS' 
pass for anyone who wants to propagate the environment CFLAGS into the 
kernel build.

	Ingo
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