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aarch64: vp9mc: Load only 12 pixels in the 4 pixel wide horizontal filter

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This reduces the amount the horizontal filters read beyond the filter
width to a consistent 1 pixel. The data is not used so this is usually
not noticeable. It becomes a problem when the application allocates
frame buffers only for the aligned picture size and the end of it is at
a page boundary. This happens for picture sizes which are a multiple of
the page size like 1280x640. The frame buffer allocation is based on
its most likely done via mmap + MAP_ANONYMOUS so start and end of the
buffer are page aligned and the previous and next page are not
necessarily mapped.
Under these conditions like seen by Firefox a read beyond the end of the
buffer results in a segfault.
After the over-read is reduced to a single pixel it's reasonable to use
VP9's emulated edge motion compensation for this.

Fixes: https://bugzilla.mozilla.org/show_bug.cgi?id=1881185
Signed-off-by: Janne Grunau <janne-ffmpeg@jannau.net>
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>
(cherry picked from commit 430c38f698)
This commit is contained in:
Janne Grunau 2025-01-03 01:54:38 +01:00 committed by Ronald S. Bultje
parent 30cd0d7bd0
commit 7f0d4aa61c
1 changed files with 9 additions and 1 deletions
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10
libavcodec/aarch64/vp9mc_neon.S
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@ -230,6 +230,9 @@ function \type\()_8tap_\size\()h_\idx1\idx2
// reduced dst stride
.if \size >= 16
sub x1, x1, x5
.elseif \size == 4
add x12, x2, #8
add x13, x7, #8
.endif
// size >= 16 loads two qwords and increments x2,
// for size 4/8 it's enough with one qword and no
@ -248,9 +251,14 @@ function \type\()_8tap_\size\()h_\idx1\idx2
.if \size >= 16
ld1 {v4.8b, v5.8b, v6.8b}, [x2], #24
ld1 {v16.8b, v17.8b, v18.8b}, [x7], #24
.else
.elseif \size == 8
ld1 {v4.8b, v5.8b}, [x2]
ld1 {v16.8b, v17.8b}, [x7]
.else // \size == 4
ld1 {v4.8b}, [x2]
ld1 {v16.8b}, [x7]
ld1 {v5.s}[0], [x12], x3
ld1 {v17.s}[0], [x13], x3
.endif
uxtl v4.8h, v4.8b
uxtl v5.8h, v5.8b