[Mesa-dev] [PATCH v2] swr: Don't crash when encountering a VBO with stride = 0.

[Bruce Cherniak]

The swr driver uses vertex_buffer->stride to determine the number
of elements in a VBO. A recent change to the state-tracker made it
possible for VBO's with stride=0. This resulted in a divide by zero
crash in the driver. The solution is to use the pre-calculated vertex
element stream_pitch in this case.

This patch fixes the crash in a number of piglit and VTK tests introduced
by 17f776c27be266f2.

There are several VTK tests that still crash and need proper handling of
vertex_buffer_index.  This will come in a follow-on patch.

v2: Correctly update all parameters for VBO constants (stride = 0).
    Also fixes the remaining crashes/regressions that v1 did
    not address, without touching vertex_buffer_index.
---
 src/gallium/drivers/swr/swr_state.cpp | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/src/gallium/drivers/swr/swr_state.cpp b/src/gallium/drivers/swr/swr_state.cpp
index 08549e51a1..316872581d 100644
--- a/src/gallium/drivers/swr/swr_state.cpp
+++ b/src/gallium/drivers/swr/swr_state.cpp
@@ -1247,13 +1247,24 @@ swr_update_derived(struct pipe_context *pipe,
 
          pitch = vb->stride;
          if (!vb->is_user_buffer) {
-            /* VBO
-             * size is based on buffer->width0 rather than info.max_index
-             * to prevent having to validate VBO on each draw */
-            size = vb->buffer.resource->width0;
-            elems = size / pitch;
-            partial_inbounds = size % pitch;
-            min_vertex_index = 0;
+            /* VBO */
+            if (!pitch) {
+               /* If pitch=0 (ie vb->stride), buffer contains a single
+                * constant attribute.  Use the stream_pitch which was
+                * calculated during creation of vertex_elements_state for the
+                * size of the attribute. */
+               size = ctx->velems->stream_pitch[i];
+               elems = 1;
+               partial_inbounds = 0;
+               min_vertex_index = 0;
+            } else {
+               /* size is based on buffer->width0 rather than info.max_index
+                * to prevent having to validate VBO on each draw. */
+               size = vb->buffer.resource->width0;
+               elems = size / pitch;
+               partial_inbounds = size % pitch;
+               min_vertex_index = 0;
+            }
 
             p_data = swr_resource_data(vb->buffer.resource) + vb->buffer_offset;
          } else {
-- 
2.11.0