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mpegplayer: Fix aliasing rules violation on multi-core targets

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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
This commit is contained in:
Solomon Peachy 2020-07-24 22:46:05 -04:00
parent 677848cf80
commit 469866b6c9
1 changed files with 5 additions and 3 deletions
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8
apps/plugins/mpegplayer/video_out_rockbox.c
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@ -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