Fix crash on scaling on OS X.

diff --git a/src/lib/image.cc b/src/lib/image.cc
index f9a42f93b2fc572345fab5d54eef6885361ca869..dbea62d26b3b7363d7c33ce7df19dff170430a5f 100644 (file)
--- a/src/lib/image.cc
+++ b/src/lib/image.cc
@@ -422,7 +422,17 @@ Image::allocate ()
        for (int i = 0; i < components(); ++i) {
                _line_size[i] = ceil (_size.width * bytes_per_pixel(i));
                _stride[i] = stride_round_up (i, _line_size, _aligned ? 32 : 1);
-               _data[i] = (uint8_t *) av_malloc (_stride[i] * lines (i));
+
+               /* The assembler function ff_rgb24ToY_avx (in libswscale/x86/input.asm)
+                  uses a 16-byte fetch to read three bytes (R/G/B) of image data.
+                  Hence on the last pixel of the last line it reads over the end of
+                  the actual data by 1 byte.  If the width of an image is a multiple
+                  of the stride alignment there will be no padding at the end of image lines.
+                  OS X crashes on this illegal read, though other operating systems don't
+                  seem to mind.  The nasty + 1 in this malloc makes sure there is always a byte
+                  for that instruction to read safely.
+               */
+               _data[i] = (uint8_t *) av_malloc (_stride[i] * lines (i) + 1);
        }
 }