[Mesa-dev] [PATCH] i965: Use memcpy instead of an assignment when storing uniforms

[Neil Roberts]

The i965 driver uses a float pointer to point to the value of a uniform and
also as the destination within the batch buffer. However the same locations
can also be used to store values for integer uniforms. Previously the value
was being copied into the batch buffer with a regular assignment. This breaks
if the compiler does this by loading and saving through an x87 register
because the fst instruction tries to fix up invalid float values. That can
corrupt some specific integer values. This patch changes it to use a memcpy
instead so that it won't use a floating-point register.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=81150
---
 src/mesa/drivers/dri/i965/gen6_vs_state.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/gen6_vs_state.c b/src/mesa/drivers/dri/i965/gen6_vs_state.c
index 905e123..cdbc083 100644
--- a/src/mesa/drivers/dri/i965/gen6_vs_state.c
+++ b/src/mesa/drivers/dri/i965/gen6_vs_state.c
@@ -81,7 +81,13 @@ gen6_upload_push_constants(struct brw_context *brw,
        * wouldn't be set for them.
       */
       for (i = 0; i < prog_data->nr_params; i++) {
-         param[i] = *prog_data->param[i];
+         /* A memcpy is used here instead of a regular assignment because
+          * otherwise the value may end up being copied through a
+          * floating-point register. This will break if the x87 registers are
+          * used and we are storing an integer value here because the fst
+          * instruction tries to fix up invalid values and that would corrupt
+          * an integer value */
+         memcpy(param + i, prog_data->param[i], sizeof param[i]);
       }
 
       if (0) {
-- 
1.9.3