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From:   Randy Dunlap <rdunlap@infradead.org>
Subject: Re: gpu: drm_fb_cma_helper.c:46: undefined reference to
 `drm_gem_fb_get_obj'
To:     Thomas Zimmermann <tzimmermann@suse.de>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        dri-devel@lists.freedesktop.org,
        open list <linux-kernel@vger.kernel.org>,
        Linux-Next Mailing List <linux-next@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Arnd Bergmann <arnd@arndb.de>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>
References: <CA+G9fYvpyUbqLko+9Dza8h4=9yOd-n9J0dKoQtZxawstCCnsZw@mail.gmail.com>
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Message-ID: <6862b109-ea12-6ffa-c82b-b23ee26aa5b2@infradead.org>
Date:   Tue, 26 Oct 2021 17:58:34 -0700
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On 10/26/21 11:21 AM, Thomas Zimmermann wrote:
> Hi
> 
> Am 25.10.21 um 14:13 schrieb Naresh Kamboju:
>> Regression found on arm gcc-11 built with multi_v5_defconfig
>> Following build warnings / errors reported on linux next 20211025.
>>
>> metadata:
>>      git_describe: next-20211025
>>      git_repo: https://gitlab.com/Linaro/lkft/mirrors/next/linux-next
>>      git_short_log: 9ae1fbdeabd3 (\"Add linux-next specific files for 20211025\")
>>      target_arch: arm
>>      toolchain: gcc-11
>>      config: multi_v5_defconfig
>>
>> build error :
>> --------------
>> arm-linux-gnueabihf-ld: drivers/gpu/drm/drm_fb_cma_helper.o: in
>> function `drm_fb_cma_get_gem_obj':
>> drivers/gpu/drm/drm_fb_cma_helper.c:46: undefined reference to
>> `drm_gem_fb_get_obj'
>> arm-linux-gnueabihf-ld: drivers/gpu/drm/drm_fb_cma_helper.c:46:
>> undefined reference to `drm_gem_fb_get_obj'
>> arm-linux-gnueabihf-ld: drivers/gpu/drm/drm_fb_cma_helper.c:46:
>> undefined reference to `drm_gem_fb_get_obj'
>> arm-linux-gnueabihf-ld: drivers/gpu/drm/drm_fb_cma_helper.o: in
>> function `drm_fb_cma_sync_non_coherent':
>> drivers/gpu/drm/drm_fb_cma_helper.c:133: undefined reference to
>> `drm_atomic_helper_damage_iter_init'
>> arm-linux-gnueabihf-ld: drivers/gpu/drm/drm_fb_cma_helper.c:135:
>> undefined reference to `drm_atomic_helper_damage_iter_next'
>> make[1]: *** [Makefile:1252: vmlinux] Error 1
>> make[1]: Target '__all' not remade because of errors.
>> make: *** [Makefile:226: __sub-make] Error 2
>>
>> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
>>
>>
>> build link:
>> -----------
>> https://builds.tuxbuild.com/1zzgFZBGjpQ5R0lawQFW9iJ39Hp/build.log
>>
>> build config:
>> -------------
>> https://builds.tuxbuild.com/1zzgFZBGjpQ5R0lawQFW9iJ39Hp/config
> 
> Looking at this config, there is:
> 
> CONFIG_DRM=y
> # CONFIG_DRM_DP_AUX_CHARDEV is not set
> # CONFIG_DRM_DEBUG_MM is not set
> # CONFIG_DRM_DEBUG_SELFTEST is not set
> CONFIG_DRM_KMS_HELPER=m
> # CONFIG_DRM_LOAD_EDID_FIRMWARE is not set
> # CONFIG_DRM_DP_CEC is not set
> CONFIG_DRM_GEM_CMA_HELPER=y
> CONFIG_DRM_KMS_CMA_HELPER=y
> 
> GEM_CMA_HELPER depends on KMS_HELPER, but the latter is a module. That's probably the cause of the problem. Is it intentionally set this way?
> 

The only drivers that select DRM_KMS_HELPER are both =m, so that's how
DRM_KMS_HELPER is set also.

Symbol: DRM_KMS_HELPER [=m]
Type : tristate
Defined at drivers/gpu/drm/Kconfig:82
Depends on: HAS_IOMEM [=y] && DRM [=y]
Selected by [m]:
- DRM_ATMEL_HLCDC [=m] && HAS_IOMEM [=y] && DRM [=y] && OF [=y] && COMMON_CLK [=y] && MFD_ATMEL_HLCDC [=y] && ARM [=y]
- DRM_ASPEED_GFX [=m] && HAS_IOMEM [=y] && DRM [=y] && OF [=y] && (COMPILE_TEST [=n] || ARCH_ASPEED [=y]) && MMU [=y]


I did the ARM cross-build and also see the linker error.
I didn't understand why -- and still don't, but here is a little
speculation:

In the past (e.g. 10 years ago), we have to move some .o files
in lib/ from lib-y to obj-y so that they would always be included
in the final object file and not cause their user/caller object
files to suffer from undefined references.
These happened because unused functions(?) in lib-y files are
stripped out of the final object files.
The same thing could be happening here (still just guessing).

Does that help any?  I dunno.

Adding Arnd to Cc: to see if he has any ideas...

>>
>> # To install tuxmake on your system globally
>> # sudo pip3 install -U tuxmake
>> tuxmake --runtime podman --target-arch arm --toolchain gcc-11
>> --kconfig multi_v5_defconfig
>>
>> -- 
>> Linaro LKFT
>> https://lkft.linaro.org


-- 
~Randy