linux-kernel - Re: [PATCH] ARM: Kconfig: default to AEABI w/ Clang

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Date:   Thu, 4 Jul 2019 09:56:13 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Mark Brown <broonie@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Paul Burton <paul.burton@...s.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marc Zyngier <marc.zyngier@....com>
Subject: Re: [PATCH] ARM: Kconfig: default to AEABI w/ Clang

On Thu, Jul 04, 2019 at 10:29:35AM +0200, Arnd Bergmann wrote:
> On Thu, Jul 4, 2019 at 10:13 AM Linus Walleij <linus.walleij@...aro.org> wrote:
> > On Tue, Jun 25, 2019 at 11:04 PM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> >
> > > Clang produces references to __aeabi_uidivmod and __aeabi_idivmod for
> > > arm-linux-gnueabi and arm-linux-gnueabihf targets incorrectly when AEABI
> > > is not selected (such as when OABI_COMPAT is selected).
> > >
> > > While this means that OABI userspaces wont be able to upgraded to
> > > kernels built with Clang, it means that boards that don't enable AEABI
> > > like s3c2410_defconfig will stop failing to link in KernelCI when built
> > > with Clang.
> > >
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/482
> > > Link: https://groups.google.com/forum/#!msg/clang-built-linux/yydsAAux5hk/GxjqJSW-AQAJ
> > > Suggested-by: Arnd Bergmann <arnd@...db.de>
> > > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> >
> > As reflecting the state of things with CLANG it's:
> > Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> >
> > But I think we in general need to have some discussion on how to
> > proceed with OABI userspaces.
> >
> > I am well aware of distributions like OpenWrt using EABI even
> > on ARMv4 with "tricks" like this:
> > https://github.com/openwrt/openwrt/blob/master/toolchain/gcc/patches/9.1.0/840-armv4_pass_fix-v4bx_to_ld.patch
> 
> I did not expect that to be necessary in gcc as long as it supports
> building for armv4 (non-t), but I might be missing something here.
> 
> > I have one OABI that I can think of would be nice to live on
> > and it's the RedHat derivative on my Foorbridge NetWinder.
> > OK I wouldn't cry if we have to kill it because it is too hard to
> > keep supporting it, but it has been running the latest kernels
> > all along so if it's not a huge effort I'd be interested in knowing
> > the options.
> 
> But do you see any problems with cross-compiling kernels to
> EABI with CONFIG_OABI_COMPAT for machines like that?

Yes, there are a few ioctls that break.

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