linux-kernel - Re: x86 - clang / objtool status

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Date:   Thu, 18 Jul 2019 13:58:39 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org
Subject: Re: x86 - clang / objtool status

Hi Thomas,

I can't comment on the objtool stuff as it is a bit outside of my area
of expertise (probably going to be my next major learning project) but I
can comment on the other errors.

On Thu, Jul 18, 2019 at 10:40:09PM +0200, Thomas Gleixner wrote:
>  Build fails with:
> 
>   clang-10: error: unknown argument: '-mpreferred-stack-boundary=4'
>   make[5]: *** [linux/scripts/Makefile.build:279: drivers/gpu/drm/amd/amdgpu/../display/dc/dcn20/dcn20_resource.o] Error 1

Arnd sent a patch for this which has been picked up:
https://lore.kernel.org/lkml/CADnq5_Mm=Fj4AkFtuo+W_295q8r6DY3Sumo7gTG-McUYY=CeVg@mail.gmail.com/

> 3) allmodconfig:
>  Build fails with:
> 
>   ERROR: "__compiletime_assert_2801" [drivers/net/wireless/intel/iwlwifi/iwlwifi.ko] undefined!
>   ERROR: "__compiletime_assert_2446" [drivers/net/wireless/intel/iwlwifi/iwlwifi.ko] undefined!
>   ERROR: "__compiletime_assert_2452" [drivers/net/wireless/intel/iwlwifi/iwlwifi.ko] undefined!
>   ERROR: "__compiletime_assert_2790" [drivers/net/wireless/intel/iwlwifi/iwlwifi.ko] undefined!

Being tracked here:
https://github.com/ClangBuiltLinux/linux/issues/580

It is a clang bug but has a kernel side fix. Nick sent one but it sounds
like Intel has another one pending:

https://lore.kernel.org/lkml/20190712001708.170259-1-ndesaulniers@google.com/

https://lore.kernel.org/lkml/da053a97d771eff0ad8db37e644108ed2fad25a3.camel@coelho.fi/

>  This also emits a boatload of warnings like this:
> 
>   linux/fs/nfs/dir.c:451:34: warning: variable 'wq' is uninitialized when used within its own initialization
>       [-Wuninitialized]
>         DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
>                                         ^~
>   linux/include/linux/wait.h:74:63: note: expanded from macro 'DECLARE_WAIT_QUEUE_HEAD_ONSTACK'
>         struct wait_queue_head name = __WAIT_QUEUE_HEAD_INIT_ONSTACK(name)
>                                ~~~~                                  ^~~~
>   linux/include/linux/wait.h:72:33: note: expanded from macro '__WAIT_QUEUE_HEAD_INIT_ONSTACK'
>         ({ init_waitqueue_head(&name); name; })

Being tracked here:
https://github.com/ClangBuiltLinux/linux/issues/499

Has a kernel workaround patch posted but it should be fixed in clang:

https://lore.kernel.org/lkml/20190703081119.209976-1-arnd@arndb.de/

https://bugs.llvm.org/show_bug.cgi?id=42604

Thanks for continuing to test it and keeping us posted on the issues!
Nathan