[Mesa-stable] [Mesa-dev] [PATCH] mesa: do not use _glapi_new_nop_table() for DRI builds

[Ian Romanick]

On 05/21/2015 06:19 PM, Brian Paul wrote:
> Commit 4bdbb588a9d38 introduced new _glapi_new_nop_table() and
> _glapi_set_nop_handler() functions in the glapi dispatcher (which
> live in libGL.so).  The calls to those functions from context.c
> would be undefined (i.e. an ABI break) if the libGL used at runtime
> was older.
> 
> For the time being, use the old single generic_nop() function for
> non-Windows builds to avoid this problem.  At some point in the future
> it should be safe to remove this work-around.  See comments for more
> details.
> 
> v2: Incorporate feedback from Emil.  Use _WIN32 instead of
> GLX_DIRECT_RENDERING to control behavior, move comments.
> 
> Cc: 10.6 <mesa-stable at lists.freedesktop.org>
> ---
>  src/mesa/main/context.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 60 insertions(+), 2 deletions(-)
> 
> diff --git a/src/mesa/main/context.c b/src/mesa/main/context.c
> index 544cc14..02875ba 100644
> --- a/src/mesa/main/context.c
> +++ b/src/mesa/main/context.c
> @@ -883,6 +883,19 @@ update_default_objects(struct gl_context *ctx)
>  }
>  
>  
> +/* XXX this is temporary and should be removed at some point in the
> + * future when there's a reasonable expectation that the libGL library
> + * contains the _glapi_new_nop_table() and _glapi_set_nop_handler()
> + * functions which were added in Mesa 10.6.
> + */

The other way would be to use dlsym determine whether or not the
function is available.  That should work on most or all ELF systems.  We
could also use the usual DRI extension mechanism.  That's the generally
accepted way to advertise new, optional libGL functionality to drivers.

Either way, this patch is

Reviewed-and-tested-by: Ian Romanick <ian.d.romanick at intel.com>

> +#if !defined(_WIN32)
> +/* Avoid libGL / driver ABI break */
> +#define USE_GLAPI_NOP_FEATURES 0
> +#else
> +#define USE_GLAPI_NOP_FEATURES 1
> +#endif
> +
> +
>  /**
>   * This function is called by the glapi no-op functions.  For each OpenGL
>   * function/entrypoint there's a simple no-op function.  These "no-op"
> @@ -898,6 +911,7 @@ update_default_objects(struct gl_context *ctx)
>   *
>   * \param name  the name of the OpenGL function
>   */
> +#if USE_GLAPI_NOP_FEATURES
>  static void
>  nop_handler(const char *name)
>  {
> @@ -914,6 +928,7 @@ nop_handler(const char *name)
>     }
>  #endif
>  }
> +#endif
>  
>  
>  /**
> @@ -923,7 +938,45 @@ nop_handler(const char *name)
>  static void GLAPIENTRY
>  nop_glFlush(void)
>  {
> -   /* don't record an error like we do in _mesa_generic_nop() */
> +   /* don't record an error like we do in nop_handler() */
> +}
> +#endif
> +
> +
> +#if !USE_GLAPI_NOP_FEATURES
> +static int
> +generic_nop(void)
> +{
> +   GET_CURRENT_CONTEXT(ctx);
> +   _mesa_error(ctx, GL_INVALID_OPERATION,
> +               "unsupported function called "
> +               "(unsupported extension or deprecated function?)");
> +   return 0;
> +}
> +#endif
> +
> +
> +/**
> + * Create a new API dispatch table in which all entries point to the
> + * generic_nop() function.  This will not work on Windows because of
> + * the __stdcall convention which requires the callee to clean up the
> + * call stack.  That's impossible with one generic no-op function.
> + */
> +#if !USE_GLAPI_NOP_FEATURES
> +static struct _glapi_table *
> +new_nop_table(unsigned numEntries)
> +{
> +   struct _glapi_table *table;
> +
> +   table = malloc(numEntries * sizeof(_glapi_proc));
> +   if (table) {
> +      _glapi_proc *entry = (_glapi_proc *) table;
> +      unsigned i;
> +      for (i = 0; i < numEntries; i++) {
> +         entry[i] = (_glapi_proc) generic_nop;
> +      }
> +   }
> +   return table;
>  }
>  #endif
>  
> @@ -941,7 +994,11 @@ alloc_dispatch_table(void)
>      * Mesa we do this to accommodate different versions of libGL and various
>      * DRI drivers.
>      */
> -   GLint numEntries = MAX2(_glapi_get_dispatch_table_size(), _gloffset_COUNT);
> +   int numEntries = MAX2(_glapi_get_dispatch_table_size(), _gloffset_COUNT);
> +
> +#if !USE_GLAPI_NOP_FEATURES
> +   struct _glapi_table *table = new_nop_table(numEntries);
> +#else
>     struct _glapi_table *table = _glapi_new_nop_table(numEntries);
>  
>  #if defined(_WIN32)
> @@ -967,6 +1024,7 @@ alloc_dispatch_table(void)
>  #endif
>  
>     _glapi_set_nop_handler(nop_handler);
> +#endif
>  
>     return table;
>  }
>