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[FFmpeg-devel,2/7] avcodec/motion_est_template: Avoid using last + 1 element of array

Message ID AS8P250MB074458CE283166E83287B5958F2D9@AS8P250MB0744.EURP250.PROD.OUTLOOK.COM
State Accepted
Commit 7c5d256c9c6f8361cd9dde24544b61cec177b3ec
Headers show
Series [FFmpeg-devel,1/7] avcodec/snow_dwt: Fix left shifts of negative numbers | expand

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Context Check Description
yinshiyou/make_loongarch64 success Make finished
yinshiyou/make_fate_loongarch64 success Make fate finished

Commit Message

Andreas Rheinhardt Oct. 21, 2022, 6:59 p.m. UTC 
For an int array[8][2] using &array[8][0] (which is an int*
pointing to the element beyond the last element of array)
triggers a "runtime error: index 8 out of bounds for type 'int[8][2]'"
from (Clang-)UBSan in the fate-vsynth(1|2|_lena)-snow tests.

I don't know whether this is really undefined behaviour or does not
actually fall under the "pointer arithmetic with the element beyond
the last element of the array is allowed as long as it is not
accessed" exception". All I know is that the code itself does not
read from beyond the last element of the array.

Nevertheless rewrite the code to a form that UBSan does not complain
about.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/motion_est_template.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

diff --git a/libavcodec/motion_est_template.c b/libavcodec/motion_est_template.c
index f3e94b7ebb..1888697db7 100644
--- a/libavcodec/motion_est_template.c
+++ b/libavcodec/motion_est_template.c
@@ -281,7 +281,7 @@  static int qpel_motion_search(MpegEncContext * s,
                     for(i=0; i<8; i++){
                         if(score < best[i]){
                             memmove(&best[i+1], &best[i], sizeof(int)*(7-i));
-                            memmove(&best_pos[i+1][0], &best_pos[i][0], sizeof(int)*2*(7-i));
+                            memmove(&best_pos[i + 1], &best_pos[i], sizeof(*best_pos) * (7 - i));
                             best[i]= score;
                             best_pos[i][0]= nx + 4*mx;
                             best_pos[i][1]= ny + 4*my;