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

[Brian Paul]

On 05/26/2015 12:07 PM, Ian Romanick wrote:
> 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.

OK, I can look into that someday.

>
> Either way, this patch is
>
> Reviewed-and-tested-by: Ian Romanick <ian.d.romanick at intel.com>

Thanks!

-Brian

>
>> +#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;
>>   }
>>
>