[vlc-devel] [PATCH 1/2] egl: Import GLES symbols with a direct library dlopen

[Thomas Guillem]

On Tue, May 22, 2018, at 16:59, Rémi Denis-Courmont wrote:
> Le tiistaina 22. toukokuuta 2018, 17.32.43 EEST Paul Kocialkowski a écrit :
> > It appears that some EGL blobs (usually used with GLES) don't expose all
> > the required core GLES API functions through eglGetProcAddress.
> 
> AFAICT, this is undefined behaviour. This might be fine for an embedded build 
> where you know the bugs in your driver, but it looks totally unsafe in 
> general, and therefore unacceptable in upstream VLC.

cf. https://www.khronos.org/registry/EGL/extensions/KHR/EGL_KHR_get_all_proc_addresses.txt
eglGetProcAddress() is only required to resolve non-extension symbols (so core only).
And VLC uses eglGetProcAddress() to fetch extension symbols.

> 
> > 
> > Resort to mapping these symbols using dlopen directly instead.
> > 
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski at bootlin.com>
> > ---
> >  modules/video_output/opengl/egl.c | 28 ++++++++++++++++++++++++++--
> >  1 file changed, 26 insertions(+), 2 deletions(-)
> > 
> > diff --git a/modules/video_output/opengl/egl.c
> > b/modules/video_output/opengl/egl.c index 9162675447..0477be5474 100644
> > --- a/modules/video_output/opengl/egl.c
> > +++ b/modules/video_output/opengl/egl.c
> > @@ -26,6 +26,7 @@
> > 
> >  #include <stdlib.h>
> >  #include <assert.h>
> > +#include <dlfcn.h>
> >  #include <EGL/egl.h>
> >  #include <EGL/eglext.h>
> > 
> > @@ -43,6 +44,8 @@
> >  # include "../android/utils.h"
> >  #endif
> > 
> > +#define LIBGLESv2_DL_NAME "libGLESv2.so.2"
> > +
> >  typedef struct vlc_gl_sys_t
> >  {
> >      EGLDisplay display;
> > @@ -57,6 +60,8 @@ typedef struct vlc_gl_sys_t
> >  #endif
> >      PFNEGLCREATEIMAGEKHRPROC    eglCreateImageKHR;
> >      PFNEGLDESTROYIMAGEKHRPROC   eglDestroyImageKHR;
> > +    bool is_gles;
> 
> No way. We already track the API.
> 
> > +    void *gles_handle;
> >  } vlc_gl_sys_t;
> > 
> >  static int MakeCurrent (vlc_gl_t *gl)
> > @@ -101,8 +106,12 @@ static void SwapBuffers (vlc_gl_t *gl)
> > 
> >  static void *GetSymbol(vlc_gl_t *gl, const char *procname)
> >  {
> > -    (void) gl;
> > -    return (void *)eglGetProcAddress (procname);
> > +    vlc_gl_sys_t *sys = gl->sys;
> > +
> > +    if (sys->is_gles)
> > +        return dlsym(sys->gles_handle, procname);
> > +    else
> > +        return (void *)eglGetProcAddress (procname);
> >  }
> > 
> >  static const char *QueryString(vlc_gl_t *gl, int32_t name)
> > @@ -220,6 +229,10 @@ static void Close (vlc_object_t *obj)
> >      AWindowHandler_releaseANativeWindow(gl->surface->handle.anativewindow,
> >                                          AWindow_Video);
> >  #endif
> > +
> > +    if (sys->is_gles && sys->gles_handle != NULL)
> > +        dlclose(sys->gles_handle);
> > +
> >      free (sys);
> >  }
> > 
> > @@ -238,6 +251,8 @@ static int Open (vlc_object_t *obj, const struct gl_api
> > *api) sys->surface = EGL_NO_SURFACE;
> >      sys->eglCreateImageKHR = NULL;
> >      sys->eglDestroyImageKHR = NULL;
> > +    sys->is_gles = api->api == EGL_OPENGL_ES_API;
> > +    sys->gles_handle = NULL;
> > 
> >      vout_window_t *wnd = gl->surface;
> >      EGLSurface (*createSurface)(EGLDisplay, EGLConfig, void *, const EGLint
> > *) @@ -392,6 +407,15 @@ static int Open (vlc_object_t *obj, const struct
> > gl_api *api) }
> >      sys->context = ctx;
> > 
> > +    if (sys->is_gles) {
> > +        sys->gles_handle = dlopen(LIBGLESv2_DL_NAME, RTLD_NOW);
> > +	if (sys->gles_handle == NULL)
> > +        {
> > +            msg_Err (obj, "cannot get GLES library handle from dlopen");
> > +            goto error;
> > +        }
> > +    }
> > +
> >      /* Initialize OpenGL callbacks */
> >      gl->ext = VLC_GL_EXT_EGL;
> >      gl->makeCurrent = MakeCurrent;
> 
> 
> -- 
> レミ・デニ-クールモン
> http://www.remlab.net/
> 
> 
> 
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