[Mesa-dev] [PATCH V3 1/2] glsl: don't attempt to link empty program

[Timothy Arceri]

On Mon, 2016-01-25 at 16:58 -0800, Ian Romanick wrote:
> On 01/25/2016 04:46 PM, Timothy Arceri wrote:
> > Previously an empty program would go through the entire
> > link_shaders() function and we would have to be careful
> > not to cause a segfault.
> > 
> > In core profile also now set link_status to false by
> > generating an error, it was previously set to true.
> > 
> > > From Section 7.3 (PROGRAM OBJECTS) of the OpenGL 4.5 spec:
> > 
> >    "Linking can fail for a variety of reasons as specified in the
> >    OpenGL Shading Language Specification, as well as any of the
> >    following reasons:
> > 
> >     - No shader objects are attached to program."
> > 
> > V2: Only generate an error in core profile and add spec quote (Ian)
> > 
> > V3: generate error in ES too, remove previous check which was only
> > applying the rule to GL 4.5/ES 3.1 and above. My understand is that
> > this spec change is clarifying previously undefined behaviour and
> > therefore should be applied retrospectively. The ES CTS tests for
> > this are in ES 2 I suspect it was passing because it would have
> > generated an error for not having both a vertex and fragment
> > shader.
> > 
> > Cc: Ian Romanick <idr at freedesktop.org>
> > Cc: Tapani Pälli <tapani.palli at intel.com>
> > Cc: Ilia Mirkin <imirkin at alum.mit.edu>
> > ---
> >  src/glsl/linker.cpp | 43 ++++++++++++++++++++++-------------------
> > --
> >  1 file changed, 22 insertions(+), 21 deletions(-)
> > 
> > diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
> > index 6657777..79039a0 100644
> > --- a/src/glsl/linker.cpp
> > +++ b/src/glsl/linker.cpp
> > @@ -4105,14 +4105,34 @@
> > disable_varying_optimizations_for_sso(struct gl_shader_program
> > *prog)
> >  void
> >  link_shaders(struct gl_context *ctx, struct gl_shader_program
> > *prog)
> >  {
> > +   prog->Validated = false;
> > +   prog->_Used = false;
> > +
> > +   /* Section 7.3 (Program Objects) of the OpenGL 4.5 Core Profile
> > spec says:
> > +    *
> > +    *     "Linking can fail for a variety of reasons as specified
> > in the
> > +    *     OpenGL Shading Language Specification, as well as any of
> > the
> > +    *     following reasons:
> > +    *
> > +    *     - No shader objects are attached to program."
> > +    *
> > +    * The Compatibility Profile specification does not list the
> > error.  In
> > +    * Compatibility Profile missing shader stages are replaced by
> > +    * fixed-function.  This applies to the case where all stages
> > are
> > +    * missing.
> > +    */
> > +   if (prog->NumShaders == 0) {
> > +      if (ctx->API != API_OPENGL_COMPAT)
> > +         linker_error(prog, "no shaders attached to the
> > program\n");
> > +      return;
> 
> Does glsl-link-empty-prog-02 still pass?  Since prog->LinkStatus is
> false, I think that will cause problems.  Won't glUseProgram generate
> GL_INVALID_OPERATION?

It does pass, seems something sets the link flag to true before we get
here. Maybe the fallback code?

Anyway it makes sense to also move the prog->LinkStatus = true; to the
top so I've done that locally.


> 
> > +   }
> > +
> >     tfeedback_decl *tfeedback_decls = NULL;
> >     unsigned num_tfeedback_decls = prog-
> > >TransformFeedback.NumVarying;
> >  
> >     void *mem_ctx = ralloc_context(NULL); // temporary linker
> > context
> >  
> >     prog->LinkStatus = true; /* All error paths will set this to
> > false */
> > -   prog->Validated = false;
> > -   prog->_Used = false;
> >  
> >     prog->ARB_fragment_coord_conventions_enable = false;
> >  
> > @@ -4162,25 +4182,6 @@ link_shaders(struct gl_context *ctx, struct
> > gl_shader_program *prog)
> >     prog->Version = max_version;
> >     prog->IsES = is_es_prog;
> >  
> > -   /* From OpenGL 4.5 Core specification (7.3 Program Objects):
> > -    *     "Linking can fail for a variety of reasons as specified
> > in the OpenGL
> > -    *     Shading Language Specification, as well as any of the
> > following
> > -    *     reasons:
> > -    *
> > -    *     * No shader objects are attached to program.
> > -    *
> > -    *     ..."
> > -    *
> > -    *     Same rule applies for OpenGL ES >= 3.1.
> > -    */
> > -
> > -   if (prog->NumShaders == 0 &&
> > -       ((ctx->API == API_OPENGL_CORE && ctx->Version >= 45) ||
> > -        (ctx->API == API_OPENGLES2 && ctx->Version >= 31))) {
> > -      linker_error(prog, "No shader objects are attached to
> > program.\n");
> > -      goto done;
> > -   }
> > -
> >     /* Some shaders have to be linked with some other shaders
> > present.
> >      */
> >     if (num_shaders[MESA_SHADER_GEOMETRY] > 0 &&
> > 
>