drm-kmod: Export symbols

[emaste]

We currently rely on the kernel linker resolving undefined references against local symbols from other kernel modules. Be explicit about the symbols to export, in advance of changing that behaviour.

PR: 207898
Sponsored by: The FreeBSD Foundation

[evadot]

Wouldn't this be a pain to keep track of ?

[emaste]

It'll be a bit of a pain, but it's not too bad. I generated these largely with a sed expression: sed -E -n 's/^.*EXPORT_SYMBOL[A-Z_]*\((.*)\).*$/EXPORT_SYMS+= \1/p.

We could take the same approach as Linux and use EXPORT_SYMBOL to control this (e.g. output the symbols to a special section similar to linker sets, then process those into the export list for linking).

The alternative is to just set EXPORT_SYMS=YES but it really is a bug that we're linking against local symbols from other modules.

[emaste]

Also linuxkpi_video currently has EXPORT_SYMS=YES.

In my tree I've changed it to:

# drivers/video/aperture.c
EXPORT_SYMS+=  __aperture_remove_legacy_vga_devices
EXPORT_SYMS+=  aperture_remove_conflicting_devices
EXPORT_SYMS+=  aperture_remove_conflicting_pci_devices
EXPORT_SYMS+=  devm_aperture_acquire_for_platform_device

# drivers/video/hdmi.c
EXPORT_SYMS+=  hdmi_audio_infoframe_check
EXPORT_SYMS+=  hdmi_audio_infoframe_init
EXPORT_SYMS+=  hdmi_audio_infoframe_pack
EXPORT_SYMS+=  hdmi_audio_infoframe_pack_for_dp
EXPORT_SYMS+=  hdmi_audio_infoframe_pack_only
EXPORT_SYMS+=  hdmi_avi_infoframe_check
EXPORT_SYMS+=  hdmi_avi_infoframe_init
EXPORT_SYMS+=  hdmi_avi_infoframe_pack
EXPORT_SYMS+=  hdmi_avi_infoframe_pack_only
EXPORT_SYMS+=  hdmi_drm_infoframe_check
EXPORT_SYMS+=  hdmi_drm_infoframe_init
EXPORT_SYMS+=  hdmi_drm_infoframe_pack
EXPORT_SYMS+=  hdmi_drm_infoframe_pack_only
EXPORT_SYMS+=  hdmi_drm_infoframe_unpack_only
EXPORT_SYMS+=  hdmi_infoframe_check
EXPORT_SYMS+=  hdmi_infoframe_log
EXPORT_SYMS+=  hdmi_infoframe_pack
EXPORT_SYMS+=  hdmi_infoframe_pack_only
EXPORT_SYMS+=  hdmi_infoframe_unpack
EXPORT_SYMS+=  hdmi_spd_infoframe_check
EXPORT_SYMS+=  hdmi_spd_infoframe_init
EXPORT_SYMS+=  hdmi_spd_infoframe_pack
EXPORT_SYMS+=  hdmi_spd_infoframe_pack_only
EXPORT_SYMS+=  hdmi_vendor_infoframe_check
EXPORT_SYMS+=  hdmi_vendor_infoframe_init
EXPORT_SYMS+=  hdmi_vendor_infoframe_pack
EXPORT_SYMS+=  hdmi_vendor_infoframe_pack_only

[evadot]

I would prefer a script in the scripts directory that can generate this and put the result in a submakefile that the main ones include.

[emaste]

#338 is a short-term workaround to avoid relying on kernel misbehaviour

[pkubaj]

After applying https://bugs.freebsd.org/bugzilla/attachment.cgi?id=258740&action=diff, I'm still unable to load amdgpu on powerpc64le:

root@talos-powerpc64le:~ # kldload amdgpu
link_elf: symbol drm_helper_connector_dpms undefined
kldload: can't load amdgpu: No such file or directory
root@talos-powerpc64le:~ # kldload drm
link_elf: symbol dma_fence_wait undefined
kldload: can't load drm: No such file or directory
root@talos-powerpc64le:$/boot/modules$ nm dmabuf.ko | grep dma_fence_wait                                                                                                                                      
0000000000009210 T dma_fence_wait
0000000000008380 T dma_fence_wait_any_timeout
0000000000007660 T dma_fence_wait_timeout
root@talos-powerpc64le:$/boot/modules$ nm drm.ko | grep dma_fence_wait    
                 U dma_fence_wait

That is on 6.1.128.1402000_2.

[emaste]

This patch isn't ready yet, please test with #338 instead.

[pkubaj]

That's what I did, the pkg version is 6.1.128.1402000_2, which includes that change. I just posted here, because the discussion is relevant to the issue (symbols not exported).