linux-kernel - Re: next/master bisection: baseline.login on rk3288-rock2-square

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Message-ID: <7ed6fae6-eee8-5751-352b-f735ffb83194@collabora.com>
Date:   Sat, 6 Feb 2021 13:10:51 +0000
From:   Guillaume Tucker <guillaume.tucker@...labora.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        "kernelci-results@...ups.io" <kernelci-results@...ups.io>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Nicolas Pitre <nico@...xnic.net>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: next/master bisection: baseline.login on rk3288-rock2-square

On 05/02/2021 12:05, Ard Biesheuvel wrote:
> On Fri, 5 Feb 2021 at 09:21, Ard Biesheuvel <ardb@...nel.org> wrote:
>>
>> On Thu, 4 Feb 2021 at 22:31, Guillaume Tucker
>> <guillaume.tucker@...labora.com> wrote:
>>>
>>> On 04/02/2021 18:23, Nick Desaulniers wrote:
>>>> On Thu, Feb 4, 2021 at 10:12 AM Nathan Chancellor <nathan@...nel.org> wrote:
>>>>>
>>>>> On Thu, Feb 04, 2021 at 10:06:08AM -0800, 'Nick Desaulniers' via Clang Built Linux wrote:
>>>>>> On Thu, Feb 4, 2021 at 8:02 AM Ard Biesheuvel <ardb@...nel.org> wrote:
>>>>>>>
>>>>>>> On Thu, 4 Feb 2021 at 16:53, Guillaume Tucker
>>>>>>> <guillaume.tucker@...labora.com> wrote:
>>>>>>>>
>>>>>>>> On 04/02/2021 15:42, Ard Biesheuvel wrote:
>>>>>>>>> On Thu, 4 Feb 2021 at 12:32, Guillaume Tucker
>>>>>>>>> <guillaume.tucker@...labora.com> wrote:
>>>>>>>>>>
>>>>>>>>>> Essentially:
>>>>>>>>>>
>>>>>>>>>>   make -j18 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- LLVM=1 CC="ccache clang" zImage
>>>>>>
>>>>>> This command should link with BFD (and assemble with GAS; it's only
>>>>>> using clang as the compiler.
>>>>>
>>>>> I think you missed the 'LLVM=1' before CC="ccache clang". That should
>>>>> use all of the LLVM utilities minus the integrated assembler while
>>>>> wrapping clang with ccache.
>>>>
>>>> You're right, I missed `LLVM=1`. Adding `LD=ld.bfd` I think should
>>>> permit fallback to BFD.
>>>
>>> That was close, except we're cross-compiling with GCC for arm.
>>> So I've now built a plain next-20210203 (without Ard's fix) using
>>> this command line:
>>>
>>>     make LD=arm-linux-gnueabihf-ld.bfd -j18 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- LLVM=1 CC="ccache clang" zImage
>>>
>>> I'm using a modified Docker image gtucker/kernelci-build-clang-11
>>> with the very latest LLVM 11 and gcc-8-arm-linux-gnueabihf
>>> packages added to be able to use the GNU linker.  BTW I guess we
>>> should enable this kind of hybrid build setup on kernelci.org as
>>> well.
>>>
>>> Full build log + kernel binaries can be found here:
>>>
>>>     https://storage.staging.kernelci.org/gtucker/next-20210203-ard-fix/v5.10-rc4-24722-g58b6c0e507b7-gtucker_single-staging-41/arm/multi_v7_defconfig/clang-11/
>>>
>>> And this booted fine, which confirms it's really down to how
>>> ld.lld puts together the kernel image.  Does it actually solve
>>> the debate whether this is an issue to fix in the assembly code
>>> or at link time?
>>>
>>> Full test job details for the record:
>>>
>>>     https://lava.collabora.co.uk/scheduler/job/3176004
>>>
>>
>>
>> So the issue appears to be in the way the linker generates the
>> _kernel_bss_size symbol, which obviously has an impact, given that the
>> queued fix takes it into account in the cache_clean operation.
>>
>> On GNU ld, I see
>>
>>    479: 00065e14     0 NOTYPE  GLOBAL DEFAULT  ABS _kernel_bss_size
>>
>> whereas n LLVM ld.lld, I see
>>
>>    433: c1c86e98     0 NOTYPE  GLOBAL DEFAULT  ABS _kernel_bss_size
>>
>> and adding this value may cause the cache clean to operate on unmapped
>> addresses, or cause the addition to wrap and not perform a cache clean
>> at all.
>>
>> AFAICT, this also breaks the appended DTB case in LLVM, so this needs
>> a separate fix in any case.
> 
> I pushed a combined branch of torvalds/master, rmk/fixes (still
> containing my 9052/1 fix) and this patch to my for-kernelci branch
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/
> 
> Guillaume,
> 
> It seems there is no Clang-11 coverage there, right? Mind giving this
> branch a spin? If this fixes the regressions, we can get these queued
> up.

That's right, Clang builds are only enabled on linux-next and
mainline at the moment.  We could enable it on any other branch
where it makes sense.  How about just the main defconfig for arm,
arm64 and x86_64 on your ardb/for-kernelci branch?

For now I've run another set of builds with clang-11 and got the
following test results with your branch on staging:

  https://staging.kernelci.org/test/job/ardb/branch/for-kernelci/kernel/v5.11-rc6-146-g923ca344043a/plan/baseline/

which are all passing.

I'll reply to the thread with your patch to confirm.

Guillaume