[yocto] [meta-raspberrypi] Using the camera

[Andrei Gherzan]

On Tue, Jun 10, 2014 at 9:01 PM, Andrei Gherzan <andrei at gherzan.ro> wrote:

>
>
>
> On Mon, Jun 2, 2014 at 4:18 AM, Alex J Lennon <
> ajlennon at dynamicdevices.co.uk> wrote:
>
>>
>> On 01/06/2014 22:35, Alex J Lennon wrote:
>>
>>
>> On 01/06/2014 22:22, Alexandru Vaduva wrote:
>>
>>  This are indeed some very good news Alex J Lennon.
>>  I have some questions, but those maybe can be answered by the
>> maintainers of the meta-raspberrypi layer:
>>  Why was this change done?
>>      -PREFERRED_PROVIDER_virtual/egl ?= "vc-graphics-hardfp"
>>      -PREFERRED_PROVIDER_virtual/libgles2 ?= "vc-graphics-hardfp"
>>      +PREFERRED_PROVIDER_virtual/egl ?= "userland"
>>      +PREFERRED_PROVIDER_virtual/libgles2 ?= "userland"
>>  How it may affect other applications?
>>  Andrei: Do you have any input on this?
>>
>>
>>
>> I think I've worked out what is happening. It looks like an interesting,
>> and pretty obscure, effect of the default bitbake linker flags.
>>
>> There's an __attribute__(constructor) decorated function that is supposed
>> to be executed when libmmal_vc_client.so is loaded.
>>
>> However by default bitbake passes in LDFLAGS of --as-needed which means
>> that although raspivid is set to be linked against libmmal_vc_client, the
>> dependency, which is un-needed by raspivid as there's no call into that
>> library, is removed.
>>
>> The userland code for Raspivid tries to create a component with a call
>> to  mmal_component_create() which is in libmmal_core
>>
>> ref:
>> https://github.com/raspberrypi/userland/blob/master/host_applications/linux/apps/raspicam/RaspiVid.c
>>
>> This function goes to a default constructor     which walks a list
>> mmal_component_supplier_create(const char *name, MMAL_COMPONENT_T
>> *component)
>>
>> ref:
>> https://github.com/raspberrypi/userland/blob/master/interface/mmal/core/mmal_component.c
>>
>> The function that populates the supplier list,
>> mmal_component_supplier_register(), is called from a function in another
>> library, libmmal_vc_client, which is decorated with
>>
>> MMAL_CONSTRUCTOR(mmal_register_component_videocore);
>>
>> which is defined as
>>
>> # define MMAL_CONSTRUCTOR(func) void __attribute__((constructor,used))
>> func(void)
>>
>> i.e. This registration function would normally execute when the library
>> it lives in is loaded, but because there's no call into that library from
>> raspivid, and because we linked with --as-needed, the library is removed
>> from the executable's dependency list, and the components are never
>> registered...
>>
>> Diffing the working and non-working raspivids,
>>
>> Dynamic Section:
>>    NEEDED               libmmal_core.so
>>    NEEDED               libmmal_util.so
>> -  NEEDED               libmmal_vc_client.so
>>    NEEDED               libvcos.so
>>
>> So if I modify the userland_git.bb to remove the --as-needed
>>
>> +LDFLAGS="-Wl,-O1 -Wl,--hash-style=gnu"
>>
>> With this change I can now build userland out of meta-raspberrypi and
>> raspivid works for me.
>>
>> Cheers,
>>
>> Alex
>>
>>
>>
>>
>>
>
> I managed to get in sync with this discussion and will come with some
> clarifications.
>
> We switched to userland because that should give the user the best
> customization for graphics libraries. So as long as we have the sources
> would be strange not to use it. But if user doesn't want to compile the
> graphics libraries, can overwrite the PREFERENCE as needed. But generally
> building packages from source would avoid incompatibilities and some of the
> issues (linkage etc). But this is an example which proves that this can add
> issues too.
>
> Now specific to this problem, I understand it, and the the fix that
> follows this discussion seems to be right. Just heading to merges. Thanks a
> lot guys (sorry for delay - will try to be more responsive).
>

I merged the patches but there is a strange behavior. With --as-needed
removed i still get the unneeded dependency.
 0x00000001 (NEEDED)                     Shared library: [libmmal_core.so]
 0x00000001 (NEEDED)                     Shared library: [libmmal_util.so]
 0x00000001 (NEEDED)                     Shared library:
[libmmal_vc_client.so]
 0x00000001 (NEEDED)                     Shared library: [libvcos.so]
 0x00000001 (NEEDED)                     Shared library: [libbcm_host.so]
 0x00000001 (NEEDED)                     Shared library: [libpthread.so.0]
 0x00000001 (NEEDED)                     Shared library: [libdl.so.2]
 0x00000001 (NEEDED)                     Shared library: [librt.so.1]
 0x00000001 (NEEDED)                     Shared library: [libvchiq_arm.so]
 0x00000001 (NEEDED)                     Shared library: [libc.so.6]

Alex, can you take another look on this? It seems like somehow the fix
doesn't work for me.
-- 
*Andrei Gherzan*
m: +40.744.478.414 |  f: +40.31.816.28.12
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