linux-kernel - Re: [linux-stable-rc:linux-4.19.y 1181/1498] ERROR: "__compiletime_assert_491" [drivers/gpu/drm/i915/i915.ko] undefined!

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Date:   Thu, 5 Aug 2021 17:11:10 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>
Cc:     kernel test robot <lkp@...el.com>,
        clang-built-linux@...glegroups.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        stable@...r.kernel.org
Subject: Re: [linux-stable-rc:linux-4.19.y 1181/1498] ERROR:
 "__compiletime_assert_491" [drivers/gpu/drm/i915/i915.ko] undefined!

On Thu, Aug 05, 2021 at 04:23:40PM -0700, Nick Desaulniers wrote:
> On Thu, Aug 5, 2021 at 1:24 PM kernel test robot <lkp@...el.com> wrote:
> >
> > Hi Nick,
> >
> > First bad commit (maybe != root cause):
> >
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-4.19.y
> > head:   7457eed4b647560ae1b1800c295efc5f1db22e4b
> > commit: 7c29fd831799d09474dfdae556207b7102647a45 [1181/1498] lib/string.c: implement stpcpy
> > config: x86_64-randconfig-r024-20210805 (attached as .config)
> > compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project 31a71a393f65d9e07b5b0756fef9dd16690950ee)
> > reproduce (this is a W=1 build):
> >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         # https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/commit/?id=7c29fd831799d09474dfdae556207b7102647a45
> >         git remote add linux-stable-rc https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
> >         git fetch --no-tags linux-stable-rc linux-4.19.y
> >         git checkout 7c29fd831799d09474dfdae556207b7102647a45
> >         # save the attached .config to linux build tree
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64
> >
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@...el.com>
> >
> > All errors (new ones prefixed by >>):
> >
> > >> ERROR: "__compiletime_assert_491" [drivers/gpu/drm/i915/i915.ko] undefined!
> 
> ^ I'm actively trying to improve these diagnostics in LLVM at the
> moment. Hopefully that will make this report clearer!
> https://reviews.llvm.org/D106030

It does help :)

drivers/gpu/drm/i915/intel_engine_cs.c:466:2: error: call to '__compiletime_assert_491' declared with attribute error: BUILD_BUG_ON failed: (execlists_num_ports(execlists)) == 0 || (((execlists_num_ports(execlists)) & ((execlists_num_ports(execlists)) - 1)) != 0)
        BUILD_BUG_ON_NOT_POWER_OF_2(execlists_num_ports(execlists));
        ^
include/linux/build_bug.h:21:2: note: expanded from macro 'BUILD_BUG_ON_NOT_POWER_OF_2'
        BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
        ^
include/linux/build_bug.h:69:2: note: expanded from macro 'BUILD_BUG_ON'
        BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
        ^
include/linux/build_bug.h:45:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                    ^
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
include/linux/compiler.h:336:2: note: expanded from macro '_compiletime_assert'
        __compiletime_assert(condition, msg, prefix, suffix)
        ^
include/linux/compiler.h:329:4: note: expanded from macro '__compiletime_assert'
                        prefix ## suffix();                             \
                        ^
<scratch space>:83:1: note: expanded from here
__compiletime_assert_491
^
4 warnings and 1 error generated.

As it turns out, this has come up before and it was fixed by commit
410ed5731a65 ("drm/i915: Ensure intel_engine_init_execlist() builds with
Clang").

Greg and Sasha, could this be picked up for 4.19?

Cheers,
Nathan