[vlc-devel] [PATCH] bank: enable static modules for mach-o binaries

[Alexandre Janniaux]

Hi,

I checked whether it was working for MacOSX and I was able to
define static modules by adding the following ugly but self
contained snippet in the darwinvlc.m file:

```
int foo(int (*set)(void*,void*,int,...), void*bar)
{
    fprintf(stderr, "OK\n");
    abort();
}

__attribute__((visibility("default")))
extern int (*vlc_static_modules[])(int (*)(void*,void*,int,...), void*);

int (*vlc_static_modules[])(int (*)(void*,void*,int,...), void*) =
{
    foo,
    NULL,
};
```

It also create archives correctly in iOS, but I haven't
checked TVOS.

However, it would fail if the symbols are not defined when
linking the static archive to the binary or to dynamic VLCKit.

I assumed it could be considered more of a feature than a bug
as LibVLC cannot work without the mandatory modules anyway.

Regards,
--
Alexandre Janniaux
Videolabs

On Thu, Mar 12, 2020 at 04:35:40PM +0100, Alexandre Janniaux wrote:
> Static modules are available by overriding the vlc_static_modules
> symbol in the executable. To avoid exposing this feature by forcing the
> user to declare this symbol regardless of whether it was needed or not,
> it was only defined on ELF binaries which supports the weak attributes
> or when dynamic plugins are disabled as it becomes the only (thus
> mandatory) way to define plugins.
>
> Mach-O objects are also capable to define weak symbols, like defined
> for the VLC_WEAK symbol in the vlc_common.h file so also allow this
> mechanism when producing Mach-O objects.
>
> It is particularly useful to ship battery-included LibVLC builds and
> still allow external plugins in paths controlled by the application
> using the library.
> ---
>  src/Makefile.am    | 2 +-
>  src/modules/bank.c | 7 ++++++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/src/Makefile.am b/src/Makefile.am
> index 2b4dfcb7dd..bf2cb7e40d 100644
> --- a/src/Makefile.am
> +++ b/src/Makefile.am
> @@ -543,7 +543,7 @@ $(libvlccore_la_OBJECTS): libvlccore_objc.la
>  libvlccore_objc_la_OBJCFLAGS = $(AM_OBJCFLAGS) -fobjc-arc
>  libvlccore_objc_la_LDFLAGS = -static
>  libvlccore_la_LIBADD += libvlccore_objc.la
> -libvlccore_la_LDFLAGS +=  -Wl,-framework,Foundation -Xlinker -install_name -Xlinker @rpath/libvlccore.dylib
> +libvlccore_la_LDFLAGS +=  -Wl,-framework,Foundation -Xlinker -install_name -Xlinker @rpath/libvlccore.dylib -Wl,-U,_vlc_static_modules
>  endif
>
>  libvlc_win32_rc.$(OBJEXT): libvlc_win32_rc.rc $(top_srcdir)/extras/package/win32/libvlc.dll.manifest
> diff --git a/src/modules/bank.c b/src/modules/bank.c
> index 36c4b30cdd..a880eea6e9 100644
> --- a/src/modules/bank.c
> +++ b/src/modules/bank.c
> @@ -172,7 +172,12 @@ static vlc_plugin_t *module_InitStatic(vlc_plugin_cb entry)
>      return lib;
>  }
>
> -#if defined(__ELF__) || !HAVE_DYNAMIC_PLUGINS
> +/* With weak linking in __ELF__, there is no need to provide a definition
> + * of vlc_static_modules at build time and it will be evaluated to NULL if
> + * not provided at runtime. However, although __MACH__ implies the same runtime
> + * consequences for weak linking, it will still require the definition to exist
> + * at build time. To workaround this, we add -Wl,-U,vlc_static_modules. */
> +#if defined(__ELF__) || defined(__MACH__) || !HAVE_DYNAMIC_PLUGINS
>  VLC_WEAK
>  extern vlc_plugin_cb vlc_static_modules[];
>
> --
> 2.25.1
>