[yocto] [meta-raspberrypi] Using the camera

[Andrei Gherzan]

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).



-- 
*Andrei Gherzan*
m: +40.744.478.414 |  f: +40.31.816.28.12
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