Working with third party fork of linux kernel

raydude

First let me say: this is not your problem. It is mine and Xilinx's problem.

The code is here: https://github.com/Xilinx/linux-xlnx

It is based on version 6.1.0 of the official kernel repo.

I'm debugging the displayport output of a Xilinx MPSOC development board (specifically the Avnet UltraZed EV Carrier Board).

The display port out works on boot up once in a while. There are very few messages in dmesg when it doesn't work.

The code I am debugging is custom and written by Xilinx engineers. It is written to be kernel modules, but was by default set to be compiled in.

I changed the code to [M] so I could delay loading it until after boot to help with timing and to make debugging the code easier. (also because I thought there might be a race condition that is handled by the time the system is booted)

Changing to [M]odule required MODULE_LICENSE to be added to three C source codes and around 60 EXPORT_SYMBOL directives to be added.

However, after doing all that the kernel won't compile and because I'm a kernel novice I don't know what's going on. Here are the compiler errors:

  LD [M]  drivers/gpu/drm/xlnx/zynqmp-dpsub.ko
  LD      .tmp_vmlinux.kallsyms1
ld: Unexpected GOT/PLT entries detected!
ld: Unexpected run-time procedure linkages detected!
ld: ID map text too big or misaligned
ld: drivers/gpu/drm/display/drm_dp_mst_topology.o: in function `drm_dp_mst_duplicate_state':
/usr/src/linux/drivers/gpu/drm/display/drm_dp_mst_topology.c:4951: undefined reference to `__drm_atomic_helper_private_obj_duplicate_state'
ld: drivers/gpu/drm/display/drm_dp_mst_topology.o: in function `drm_dp_delayed_destroy_work':
/usr/src/linux/drivers/gpu/drm/display/drm_dp_mst_topology.c:4937: undefined reference to `drm_kms_helper_hotplug_event'
ld: drivers/gpu/drm/display/drm_dp_mst_topology.o: in function `drm_dp_mst_up_req_work':
/usr/src/linux/drivers/gpu/drm/display/drm_dp_mst_topology.c:3979: undefined reference to `drm_kms_helper_hotplug_event'
ld: drivers/gpu/drm/display/drm_dp_mst_topology.o: in function `drm_dp_mst_link_probe_work':
/usr/src/linux/drivers/gpu/drm/display/drm_dp_mst_topology.c:2689: undefined reference to `drm_kms_helper_hotplug_event'
make[1]: *** [scripts/Makefile.vmlinux:34: vmlinux] Error 1
make: *** [Makefile:1236: vmlinux] Error 2

I have checked and those references are defined in actual headers and in c code. I verified the the .o files have at least the text of those references.

I'm hoping one of you will have mercy on a newb and help me out.

I'm using gcc:

ultrazed ~ # gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/aarch64-unknown-linux-gnu/12/lto-wrapper
Target: aarch64-unknown-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-12.3.1_p20230526/work/gcc-12-20230526/configure --host=aarch64-unknown-linux-gnu --build=aarch64-unknown-linux-gnu --prefix=/usr --bindir=/usr/aarch64-unknown-linux-gnu/gcc-bin/12 --includedir=/usr/lib/gcc/aarch64-unknown-linux-gnu/12/include --datadir=/usr/share/gcc-data/aarch64-unknown-linux-gnu/12 --mandir=/usr/share/gcc-data/aarch64-unknown-linux-gnu/12/man --infodir=/usr/share/gcc-data/aarch64-unknown-linux-gnu/12/info --with-gxx-include-dir=/usr/lib/gcc/aarch64-unknown-linux-gnu/12/include/g++-v12 --with-python-dir=/share/gcc-data/aarch64-unknown-linux-gnu/12/python --enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt --disable-werror --with-system-zlib --enable-nls --without-included-gettext --disable-libunwind-exceptions --enable-checking=release --with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 12.3.1_p20230526 p2' --with-gcc-major-version-only --enable-libstdcxx-time --enable-lto --disable-libstdcxx-pch --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --disable-multilib --disable-fixed-point --enable-libgomp --disable-libssp --disable-libada --disable-cet --disable-systemtap --disable-valgrind-annotations --disable-vtable-verify --disable-libvtv --without-zstd --without-isl --enable-default-pie --enable-default-ssp
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.3.1 20230526 (Gentoo 12.3.1_p20230526 p2) 

raydude

So I'm learning more about Kconfig. I think I found an issue related to this.

The Xilinx GPU driver is using select DRM_KMS_HELPER in it's Kconfig, which is setting DRM_KMS_HELPER=m which causes the Makefile to exclude the very files that are needed.

#
# Modesetting helpers
#
 
drm_kms_helper-y := drm_bridge_connector.o drm_crtc_helper.o \
                drm_encoder_slave.o drm_flip_work.o \
                drm_probe_helper.o \
                drm_plane_helper.o drm_atomic_helper.o \
                drm_kms_helper_common.o \
                drm_simple_kms_helper.o drm_modeset_helper.o \
                drm_gem_atomic_helper.o \
                drm_gem_framebuffer_helper.o \
                drm_atomic_state_helper.o drm_damage_helper.o \
                drm_format_helper.o drm_self_refresh_helper.o drm_rect.o
drm_kms_helper-$(CONFIG_DRM_PANEL_BRIDGE) += bridge/panel.o
drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
obj-$(CONFIG_DRM_KMS_HELPER) += drm_kms_helper.o

I'm trying to figure out how to get DRM_KMS_HELPER=y but google hasn't shown me the light yet.

Can someone point me the right direction?

Nevermind I changed Makefile to assign this: drm_kms_helper-($CONFIG_DRM_KMS_HELPER)) and it still generated the same error messages.