linux-kernel - Re: [PATCH 2/7] ARM: LTO: avoid THUMB2

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Message-ID: <nycvar.YSQ.7.76.1802202202220.31644@knanqh.ubzr>
Date:   Tue, 20 Feb 2018 22:12:04 -0500 (EST)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
cc:     Andi Kleen <ak@...ux.intel.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] ARM: LTO: avoid THUMB2_KERNEL+LTO

On Tue, 20 Feb 2018, Arnd Bergmann wrote:

> Trying to build an LTO-Enabled kernel with Thumb2 instructions failed
> horribly for me, with an endless output of things like
> 
> ccVnNycO.s:2665: Error: thumb conditional instruction should be in IT block -- `bxne lr'
> ccVnNycO.s:7128: Error: thumb conditional instruction should be in IT block -- `strexeq r5,r2,[r3]'
> ccVnNycO.s:7258: Error: thumb conditional instruction should be in IT block -- `strexeq lr,r0,[r3]'
> ccVnNycO.s:17380: Error: thumb conditional instruction should be in IT block -- `strexeq r1,r2,[r6]'
> ccVnNycO.s:19163: Error: thumb conditional instruction should be in IT block -- `strexeq r8,r6,[r3]'
> ccVnNycO.s:22722: Error: thumb conditional instruction should be in IT block -- `strexeq r7,r1,[r0]'
> ccVnNycO.s:24105: conditional infixes are deprecated in unified syntax
> ccVnNycO.s:24105: Error: thumb conditional instruction should be in IT block -- `sbcccs r1,r1,r3'
> ccVnNycO.s:24105: Error: thumb conditional instruction should be in IT block -- `movcc r3,#0'
> ccVnNycO.s:24210: conditional infixes are deprecated in unified syntax
> ccVnNycO.s:24210: Error: thumb conditional instruction should be in IT block -- `sbcccs r2,r2,r3'
> ccVnNycO.s:24210: Error: thumb conditional instruction should be in IT block -- `movcc r3,#0'
> 
> I did not investigate this too much, disabling Thumb2 support when LTO is
> set lets me build randconfig kernels.
> 
> Since ARM_SINGLE_ARMV7M is Thumb2-only, I have to disallow LTO for V7-M
> targets.

Here's the workaround I sent you on January 2rd:

----- >*
#!/bin/bash

# work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78353

GCC_ROOT=/opt/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabihf

set -e
set -x

cd $GCC_ROOT//arm-linux-gnueabihf/bin
[ -e fat-as ] && exit 1
mv as fat-as
cat > as << EOF
#!/bin/bash
exec -a "\$0" "\$(dirname "\$0")/fat-as" -mimplicit-it=always "\$@"
EOF
chmod +x as
----- >8


Nicolas