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Code Issues Releases Activity

avfilter/vf_overlay: Don't perform UB pointer arithmetic

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This happens when the pixel format of the output does not
have an alpha channel. It leads to FATE failures with
the ffmpeg-filter_colorkey, filter-overlay-dvdsub-2397
filter-overlay,
filter-overlay_{gbrp_gbrap,nv12,nv21,yuv420,yuv420_yuva420,
yuv420p10,yuv422_yuva422,yuv422p10,yuv444_yuva444,yuv444p10}
and sub2video tests when using Clang UBSan.

Fix this by only performing the pointer arithmetic when
it is going to be used. This can be checked via variables
that compile-time constants due to inlining, so that the
checks are free. Given that the pointer is potentially
used as a function argument, the compiler could elide
the calculation, but not it can. The size of .text decreased
by 1632B with GCC 14 and by 1392B with Clang 19 (both -O3).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt
2025-06-04 03:20:02 +02:00
parent 0ae55affa3
commit eeb82a4406
1 changed files with 10 additions and 6 deletions
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16
libavfilter/vf_overlay.c
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@ -467,7 +467,7 @@ static av_always_inline void blend_plane_##depth##_##nbits##bits(AVFilterContext
int dst_hp = AV_CEIL_RSHIFT(dst_h, vsub); \
int yp = y>>vsub; \
int xp = x>>hsub; \
uint##depth##_t *s, *sp, *d, *dp, *dap, *a, *da, *ap; \
uint##depth##_t *s, *sp, *d, *dp, *dap, *a, *ap; \
int jmax, j, k, kmax; \
int slice_start, slice_end; \
const uint##depth##_t max = (1 << nbits) - 1; \
@ -486,14 +486,15 @@ static av_always_inline void blend_plane_##depth##_##nbits##bits(AVFilterContext
+ (yp + slice_start) * dst->linesize[dst_plane] \
+ dst_offset); \
ap = (uint##depth##_t *)(src->data[3] + (slice_start << vsub) * src->linesize[3]); \
dap = (uint##depth##_t *)(dst->data[3] + ((yp + slice_start) << vsub) * dst->linesize[3]); \
if (main_has_alpha) \
dap = (uint##depth##_t *)(dst->data[3] + ((yp + slice_start) << vsub) * dst->linesize[3]); \
\
for (j = slice_start; j < slice_end; j++) { \
k = FFMAX(-xp, 0); \
d = dp + (xp+k) * dst_step; \
s = sp + k; \
a = ap + (k<<hsub); \
da = dap + ((xp+k) << hsub); \
uint##depth##_t *da = main_has_alpha ? dap + ((xp+k) << hsub) : NULL; \
kmax = FFMIN(-xp + dst_wp, src_wp); \
\
if (nbits == 8 && ((vsub && j+1 < src_hp) || !vsub) && octx->blend_row[i]) { \
@ -502,7 +503,8 @@ static av_always_inline void blend_plane_##depth##_##nbits##bits(AVFilterContext
\
s += c; \
d += dst_step * c; \
da += (1 << hsub) * c; \
if (main_has_alpha) \
da += (1 << hsub) * c; \
a += (1 << hsub) * c; \
k += c; \
} \
@ -560,13 +562,15 @@ static av_always_inline void blend_plane_##depth##_##nbits##bits(AVFilterContext
} \
s++; \
d += dst_step; \
da += 1 << hsub; \
if (main_has_alpha) \
da += 1 << hsub; \
a += 1 << hsub; \
} \
dp += dst->linesize[dst_plane] / bytes; \
sp += src->linesize[i] / bytes; \
ap += (1 << vsub) * src->linesize[3] / bytes; \
dap += (1 << vsub) * dst->linesize[3] / bytes; \
if (main_has_alpha) \
dap += (1 << vsub) * dst->linesize[3] / bytes; \
} \
}
DEFINE_BLEND_PLANE(8, 8)