mpegplayer: Fix aliasing rules violation on multi-core targets

As the PP series has no sense of cache coherency between its multiple
cores, we need to ensure the vo_data structure does not share cachelines
with anything else.

This was previously done by defining a uint8_t array and trying to
access it via typecasting hell, triggering a large pile of aliasing
violation warnings on newer toolchains and/or higher optimization
levels.

Instead of violating the C spec in an undefined-behaviour-sort-of-way,
create a union of the right size and alignment, and make one of its members
the structure we care about.  Voila, everyone is happy.

Change-Id: Iad78f8132225437cd4aa10e6e5f6ae58ba996c19

1 files changed, 5 insertions, 3 deletions

diff --git a/apps/plugins/mpegplayer/video_out_rockbox.c b/apps/plugins/mpegplayer/video_out_rockbox.c
index b05a229083..ee5c3400c5 100644
--- a/apps/plugins/mpegplayer/video_out_rockbox.c
+++ b/apps/plugins/mpegplayer/video_out_rockbox.c
@@ -47,9 +47,11 @@ struct vo_data
 #if NUM_CORES > 1
 /* Cache aligned and padded to avoid clobbering other processors' cacheable
  * data */
-static uint8_t __vo_data[CACHEALIGN_UP(sizeof(struct vo_data))]
-        CACHEALIGN_ATTR;
-#define vo (*((struct vo_data *)__vo_data))
+static union {
+        uint8_t __vo_data[CACHEALIGN_UP(sizeof(struct vo_data))];
+        struct vo_data vo;
+} vo_raw CACHEALIGN_ATTR;
+#define vo vo_raw.vo
 #else
 static struct vo_data vo;
 #endif