[Buildroot] Failed to load libmmal.so from rpi-userland package via buildroot toolchain on raspberry pi 4

[Peter Seiderer]

Hello Iman,

On Sat, 28 Mar 2020 11:39:46 +0430, iman ahmadvand <iman72411 at gmail.com> wrote:

> Hi everyone.
> It seems that loading the MMAL interface shared libraries from rpi-userland
> package via simple dlopen is not possible, or more specific, the packages
> or binaries such as VLC or VLC codec plugin (libavcodec_plugin) could not
> load the libavcodec from FFmpeg which in turn depends on libmmal*.so
>
> The steps to reproduce(with BR2_PACKAGE_RPI_USERLAND enabled,
> BR2_STRIP_strip disabled, BR2_OPTIMIZE_0 enabled):
> git clone git://git.busybox.net/buildroot buildroot && cd buildroot && git
> checkout 2019.11.01
> make raspberrypi4_defconfig && make all
>
> Then in this image try to run a simple c routine with dlopen(), if you do
> so, for example, ./dltest /usr/lib/libmmal.so you will end up with:
>
> symbol 'mmal_port_payload_alloc': can't resolve symbol
> symbol 'mmal_port_payload_free': can't resolve symbol
> symbol 'mmal_port_log_category': can't resolve symbol
>

Can confirm your failure...did not (yet) find out what fails exactly, but
ldd produces the following ouput (mind the 0x00000000):

	$ ldd /usr/lib/libmmal.so
checking sub-depends for '/usr/lib/libmmal_vc_client.so'
checking sub-depends for '/usr/lib/libmmal_components.so'
checking sub-depends for '/usr/lib/libvchiq_arm.so'
checking sub-depends for '/usr/lib/libvcsm.so'
checking sub-depends for '/usr/lib/libmmal_core.so'
checking sub-depends for '/usr/lib/libmmal_util.so'
checking sub-depends for '/usr/lib/libcontainers.so'
checking sub-depends for '/usr/lib/libvcos.so'
checking sub-depends for '/lib/libc.so.0'
        ld-uClibc.so.1 => /lib/ld-uClibc.so.1 (0xb6f8b000)
        libmmal_vc_client.so => /usr/lib/libmmal_vc_client.so (0x00000000)
        libmmal_components.so => /usr/lib/libmmal_components.so (0x00000000)
        libvchiq_arm.so => /usr/lib/libvchiq_arm.so (0x00000000)
        libvcsm.so => /usr/lib/libvcsm.so (0x00000000)
        libmmal_core.so => /usr/lib/libmmal_core.so (0x00000000)
        libmmal_util.so => /usr/lib/libmmal_util.so (0x00000000)
        libcontainers.so => /usr/lib/libcontainers.so (0x00000000)
        libvcos.so => /usr/lib/libvcos.so (0x00000000)
        libc.so.0 => /lib/libc.so.0 (0x00000000)
        /lib/ld-uClibc.so.1 => /lib/ld-uClibc.so.1 (0x00000000)


After changing the buildroot toolchain from uclibc to glibc (and a full
re-build) dlopen() of /usr/lib/libmmal.so works and ldd produces the
following output:

	$ ldd /usr/lib/libmmal.so
	linux-vdso.so.1 (0xbea59000)
	libmmal_vc_client.so => /usr/lib/libmmal_vc_client.so (0xb6f5f000)
	libmmal_components.so => /usr/lib/libmmal_components.so (0xb6f44000)
	libvchiq_arm.so => /usr/lib/libvchiq_arm.so (0xb6f2e000)
	libvcsm.so => /usr/lib/libvcsm.so (0xb6f14000)
	libmmal_core.so => /usr/lib/libmmal_core.so (0xb6ef6000)
	libmmal_util.so => /usr/lib/libmmal_util.so (0xb6ed8000)
	libcontainers.so => /usr/lib/libcontainers.so (0xb6eb5000)
	libvcos.so => /usr/lib/libvcos.so (0xb6e9c000)
	libpthread.so.0 => /lib/libpthread.so.0 (0xb6e71000)
	libdl.so.2 => /lib/libdl.so.2 (0xb6e5e000)
	librt.so.1 => /lib/librt.so.1 (0xb6e47000)
	libc.so.6 => /lib/libc.so.6 (0xb6cfb000)
	/lib/ld-linux-armhf.so.3 (0xb6f8f000)

Regards,
Peter


> Or for another proof of the issue, you can run VLC with X11 to play an
> MPEG-4 video, and you will  end up with VLC could not load the codec module
> because of the same thing:
>
> main debug: loading plugins cache file /usr/lib/vlc/plugins/plugins.dat
> main warning: cannot read /usr/lib/vlc/plugins/plugins.dat: No such
> file or directory
> main debug: recursively browsing `/usr/lib/vlc/plugins'
> main warning: cannot load module
> `/usr/lib/vlc/plugins/codec/libavcodec_plugin.so' ((null)
>
> Any idea about this?
>
> Best Regards.
> IMAN.