glsl: add driconf to zero-init unintialized vars

Some games are sloppy.. perhaps because it is defined behavior for DX or
perhaps because nv blob driver defaults things to zero.

So add driconf param to force uninitialized variables to default to zero.

This issue was observed with rust, from steam store.  But has surfaced
elsewhere in the past.

Signed-off-by: Rob Clark <[email protected]>
Reviewed-by: Kenneth Graunke <[email protected]>

6 files changed, 21 insertions, 1 deletions

diff --git a/src/mesa/drivers/dri/common/drirc b/src/mesa/drivers/dri/common/drirc
index 3912d8b8c7e..af84ee82e8a 100644
--- a/src/mesa/drivers/dri/common/drirc
+++ b/src/mesa/drivers/dri/common/drirc
@@ -96,5 +96,9 @@ TODO: document the other workarounds.
         <application name="Warsow (64-bit)" executable="warsow.x86_64">
             <option name="allow_glsl_extension_directive_midshader" value="true" />
         </application>
+
+        <application name="Rust" executable="rust">
+            <option name="glsl_zero_init" value="true"/>
+        </application>
     </device>
 </driconf>
diff --git a/src/mesa/drivers/dri/common/xmlpool/t_options.h b/src/mesa/drivers/dri/common/xmlpool/t_options.h
index 4b298a46112..341c3763dee 100644
--- a/src/mesa/drivers/dri/common/xmlpool/t_options.h
+++ b/src/mesa/drivers/dri/common/xmlpool/t_options.h
@@ -337,7 +337,10 @@ DRI_CONF_OPT_BEGIN_B(always_have_depth_buffer, def) \
         DRI_CONF_DESC(en,gettext("Create all visuals with a depth buffer")) \
 DRI_CONF_OPT_END
 
-
+#define DRI_CONF_GLSL_ZERO_INIT(def) \
+DRI_CONF_OPT_BEGIN_B(glsl_zero_init, def) \
+        DRI_CONF_DESC(en,gettext("Force uninitialized variables to default to zero")) \
+DRI_CONF_OPT_END
 
 /**
  * \brief Initialization configuration options
diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_context.c
index 5e3c9d169b3..3f0c2e3b483 100644
--- a/src/mesa/drivers/dri/i965/brw_context.c
+++ b/src/mesa/drivers/dri/i965/brw_context.c
@@ -827,6 +827,8 @@ brw_process_driconf_options(struct brw_context *brw)
    ctx->Const.AllowGLSLExtensionDirectiveMidShader =
       driQueryOptionb(options, "allow_glsl_extension_directive_midshader");
 
+   ctx->Const.GLSLZeroInit = driQueryOptionb(options, "glsl_zero_init");
+
    brw->dual_color_blend_by_location =
       driQueryOptionb(options, "dual_color_blend_by_location");
 }
diff --git a/src/mesa/drivers/dri/i965/intel_screen.c b/src/mesa/drivers/dri/i965/intel_screen.c
index 1c71e09e7ad..432ab7bdb63 100644
--- a/src/mesa/drivers/dri/i965/intel_screen.c
+++ b/src/mesa/drivers/dri/i965/intel_screen.c
@@ -88,6 +88,10 @@ DRI_CONF_BEGIN
 	 DRI_CONF_DESC(en, "Perform code generation at shader link time.")
       DRI_CONF_OPT_END
    DRI_CONF_SECTION_END
+
+   DRI_CONF_SECTION_MISCELLANEOUS
+      DRI_CONF_GLSL_ZERO_INIT("false")
+   DRI_CONF_SECTION_END
 DRI_CONF_END
 };
 
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index cab315df23d..29e47debfc2 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -3536,6 +3536,11 @@ struct gl_constants
    GLboolean AllowGLSLExtensionDirectiveMidShader;
 
    /**
+    * Force uninitialized variables to default to zero.
+    */
+   GLboolean GLSLZeroInit;
+
+   /**
     * Does the driver support real 32-bit integers?  (Otherwise, integers are
     * simulated via floats.)
     */
diff --git a/src/mesa/state_tracker/st_extensions.c b/src/mesa/state_tracker/st_extensions.c
index c5ecd5a2dd7..3d27ca3a905 100644
--- a/src/mesa/state_tracker/st_extensions.c
+++ b/src/mesa/state_tracker/st_extensions.c
@@ -925,6 +925,8 @@ void st_init_extensions(struct pipe_screen *screen,
       extensions->EXT_texture_integer = GL_FALSE;
    }
 
+   consts->GLSLZeroInit = options->glsl_zero_init;
+
    consts->UniformBooleanTrue = consts->NativeIntegers ? ~0U : fui(1.0f);
 
    /* Below are the cases which cannot be moved into tables easily. */