sna/traps: Align indices for unrolled memset in row_inplace()

The compiler presumes that the uint64_t write is naturally aligned and
so may emit code that crashes with an unaligned moved. To workaround
this, make sure the write is so aligned.

References: https://bugs.freedesktop.org/show_bug.cgi?id=47418
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/sna/sna_trapezoids.c b/src/sna/sna_trapezoids.c
index 31a661e5..3a93450c 100644
--- a/src/sna/sna_trapezoids.c
+++ b/src/sna/sna_trapezoids.c
@@ -1499,6 +1499,21 @@ inplace_row(struct active_list *active, uint8_t *row, int width)
 				else
 					memset(row+lix, 0xff, rix);
 #else
+				if (lix & 1 && rix) {
+					row[lix] = 0xff;
+					lix++;
+					rix--;
+				}
+				if (lix & 2 && rix >= 2) {
+					*(uint16_t *)(row+lix) = 0xffff;
+					lix += 2;
+					rix -= 2;
+				}
+				if (lix & 4 && rix >= 4) {
+					*(uint32_t *)(row+lix) = 0xffffffff;
+					lix += 4;
+					rix -= 4;
+				}
 				while (rix >= 8) {
 					*(uint64_t *)(row+lix) = 0xffffffffffffffff;
 					lix += 8;