linux-kernel - Re: [RFC] minimum gcc version for kernel: raise to gcc-4.3 or 4.6?

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Date:   Mon, 2 Jan 2017 12:23:47 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
Cc:     Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        linux-kbuild@...r.kernel.org,
        kernel-build-reports@...ts.linaro.org,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...r.kernel.org
Subject: Re: [RFC] minimum gcc version for kernel: raise to gcc-4.3 or 4.6?

On Sat, Dec 17, 2016 at 12:29:50PM +0100, Sebastian Andrzej Siewior wrote:
> A new version is understandable. But why is an old version required?
> One thing is an enterprise distro that is "current" or "supported" and still
> stuck with gcc 4.1 because that is the version they decided to include in
> their release. This is sad. But you might want to ask yourself why you want
> the latest kernel but an old gcc / binutils.

To help isolate changes.

If you constantly upgrade everything, how do you bug hunt for a breakage?
How do you know whether it's created by the kernel, or by (eg) a later
version of gcc miscompiling the kernel.  You have a large amount of code
to start bug hunting through.

Sticking with particular tool versions long-term means that you build up
confidence in it - yes, sure, latent bugs exist, but it's easier to
bug hunt if you aren't constantly suspecting that your tools might be
broken.

For example, I build kernels with:

		gcc		binutils		built on
32-bit ARM	4.7.4		2.25			April/May 2015
64-bit ARM	4.9.2		2.25.51.20150219	Feb/April 2015

I'm not anticipating upgrading them for some time yet - the only one
which may get upgraded is the 64-bit binutils since later kernels now
complain about a missing errata workaround in that toolchain version.

I do still have some older toolchains around on some of my ARM boxes
though, even a GCC 3 version with ARM TLS support for faster builds!

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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