Mesa (master): i965: Avoid NULL pointer dereference when transform feedback is off.

[Kenneth Graunke]

Module: Mesa
Branch: master
Commit: 62a819184141133478cfdcfa76b62d5bb7e14fd5
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=62a819184141133478cfdcfa76b62d5bb7e14fd5

Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Fri Dec 30 15:35:02 2016 -0800

i965: Avoid NULL pointer dereference when transform feedback is off.

upload_3dstate_streamout can be called when there's no currently bound
transform feedback object.  In this case, we get the default object,
which has a NULL shader (previously gl_shader_program, now gl_program).

The old code did something sketchy, but which worked:

   const struct gl_transform_feedback_info *linked_xfb_info =
      &xfb_obj->shader_program->LinkedTransformFeedback;

Here, if shader_program is NULL, this would be a bogus pointer of 0x60.
But we never actually dereferenced it, so it worked out.

With Timothy's recent reworks, we actually end up dereferencing
xfb_obj->program along the way, which crashes since it's NULL.

The solution is to move this pointer initialization into the "active"
block, where we know it actually exists and won't be bogus.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99231
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
Reviewed-by: Timothy Arceri <timothy.arceri at collabora.com>

---

 src/mesa/drivers/dri/i965/gen7_sol_state.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/gen7_sol_state.c b/src/mesa/drivers/dri/i965/gen7_sol_state.c
index c9f9f1f..e6b79ed 100644
--- a/src/mesa/drivers/dri/i965/gen7_sol_state.c
+++ b/src/mesa/drivers/dri/i965/gen7_sol_state.c
@@ -228,12 +228,12 @@ upload_3dstate_streamout(struct brw_context *brw, bool active,
    /* BRW_NEW_TRANSFORM_FEEDBACK */
    struct gl_transform_feedback_object *xfb_obj =
       ctx->TransformFeedback.CurrentObject;
-   const struct gl_transform_feedback_info *linked_xfb_info =
-      xfb_obj->program->sh.LinkedTransformFeedback;
    uint32_t dw1 = 0, dw2 = 0, dw3 = 0, dw4 = 0;
    int i;
 
    if (active) {
+      const struct gl_transform_feedback_info *linked_xfb_info =
+         xfb_obj->program->sh.LinkedTransformFeedback;
       int urb_entry_read_offset = 0;
       int urb_entry_read_length = (vue_map->num_slots + 1) / 2 -
 	 urb_entry_read_offset;