mesa: fix display list 8-byte alignment issue

The _mesa_dlist_alloc() function is only guaranteed to return a pointer
with 4-byte alignment.  On 64-bit systems which don't support unaligned
loads (e.g. SPARC or MIPS) this could lead to a bus error in the VBO code.

The solution is to add a new  _mesa_dlist_alloc_aligned() function which
will return a pointer to an 8-byte aligned address on 64-bit systems.
This is accomplished by inserting a 4-byte NOP instruction in the display
list when needed.

The only place this actually matters is the VBO code where we need to
allocate a 'struct vbo_save_vertex_list' which needs to be 8-byte
aligned (just as if it were malloc'd).

The gears demo and others hit this bug.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88662
Cc: "10.4" <[email protected]>
Reviewed-by: José Fonseca <[email protected]>

1 files changed, 4 insertions, 1 deletions

diff --git a/src/mesa/vbo/vbo_save_api.c b/src/mesa/vbo/vbo_save_api.c
index 5055c221b6e..beef342bed8 100644
--- a/src/mesa/vbo/vbo_save_api.c
+++ b/src/mesa/vbo/vbo_save_api.c
@@ -375,11 +375,14 @@ _save_compile_vertex_list(struct gl_context *ctx)
     * being compiled.
     */
    node = (struct vbo_save_vertex_list *)
-      _mesa_dlist_alloc(ctx, save->opcode_vertex_list, sizeof(*node));
+      _mesa_dlist_alloc_aligned(ctx, save->opcode_vertex_list, sizeof(*node));
 
    if (!node)
       return;
 
+   /* Make sure the pointer is aligned to the size of a pointer */
+   assert((GLintptr) node % sizeof(void *) == 0);
+
    /* Duplicate our template, increment refcounts to the storage structs:
     */
    memcpy(node->attrsz, save->attrsz, sizeof(node->attrsz));