vc4: Compute max_index instead of trusting the rest of userspace.

max_index was coming from either the user telling us as part of
glDrawRangeElements, or from an incidental calculation as part of some
sort of primitive conversion fallback.  Sometimes, it was just set to the
default "I don't know" ~0 value.

If it wasn't set to the actual max index, then the kernel would reject the
draw call for allowing out-of-bounds VBO reads.  So, compute the max index
from the sizes of the VBOs, which isn't too expensive (unlike mapping and
reading the index buffer) and is reliable.

Fixes piglit vao-element-array-buffer.

1 files changed, 13 insertions, 5 deletions

diff --git a/src/gallium/drivers/vc4/vc4_draw.c b/src/gallium/drivers/vc4/vc4_draw.c
index 57fd0db905c..f4437183f99 100644
--- a/src/gallium/drivers/vc4/vc4_draw.c
+++ b/src/gallium/drivers/vc4/vc4_draw.c
@@ -142,19 +142,27 @@ vc4_draw_vbo(struct pipe_context *pctx, const struct pipe_draw_info *info)
                 vc4->prog.vs->coord_shader_offset);
         cl_u32(&vc4->shader_rec, 0); /* UBO offset written by kernel */
 
+        uint32_t max_index = 0xffff;
         for (int i = 0; i < vtx->num_elements; i++) {
                 struct pipe_vertex_element *elem = &vtx->pipe[i];
                 struct pipe_vertex_buffer *vb =
                         &vertexbuf->vb[elem->vertex_buffer_index];
                 struct vc4_resource *rsc = vc4_resource(vb->buffer);
+                uint32_t offset = vb->buffer_offset + elem->src_offset;
+                uint32_t vb_size = rsc->bo->size - offset;
+                uint32_t elem_size =
+                        util_format_get_blocksize(elem->src_format);
 
-                cl_reloc(vc4, &vc4->shader_rec, rsc->bo,
-                         vb->buffer_offset + elem->src_offset);
-                cl_u8(&vc4->shader_rec,
-                      util_format_get_blocksize(elem->src_format) - 1);
+                cl_reloc(vc4, &vc4->shader_rec, rsc->bo, offset);
+                cl_u8(&vc4->shader_rec, elem_size - 1);
                 cl_u8(&vc4->shader_rec, vb->stride);
                 cl_u8(&vc4->shader_rec, i * 16); /* VS VPM offset */
                 cl_u8(&vc4->shader_rec, i * 16); /* CS VPM offset */
+
+                if (vb->stride > 0) {
+                        max_index = MIN2(max_index,
+                                         (vb_size - elem_size) / vb->stride);
+                }
         }
 
         /* the actual draw call. */
@@ -183,7 +191,7 @@ vc4_draw_vbo(struct pipe_context *pctx, const struct pipe_draw_info *info)
                        VC4_INDEX_BUFFER_U8));
                 cl_u32(&vc4->bcl, info->count);
                 cl_reloc(vc4, &vc4->bcl, rsc->bo, vc4->indexbuf.offset);
-                cl_u32(&vc4->bcl, info->max_index);
+                cl_u32(&vc4->bcl, max_index);
         } else {
                 cl_u8(&vc4->bcl, VC4_PACKET_GL_ARRAY_PRIMITIVE);
                 cl_u8(&vc4->bcl, info->mode);