lavu: add CHK_OFFS as AV_CHECK_OFFSET to check struct member offsets

libavcodec/arm/asm-offsets.h

@@ -21,13 +21,6 @@
 #ifndef AVCODEC_ARM_ASM_OFFSETS_H
 #define AVCODEC_ARM_ASM_OFFSETS_H
 
-#ifndef __ASSEMBLER__
-#include <stddef.h>
-#define CHK_OFFS(s, m, o) struct check_##o {    \
-        int x_##o[offsetof(s, m) == o? 1: -1];  \
-    }
-#endif
-
 /* MpegEncContext */
 #define Y_DC_SCALE               0xa8
 #define C_DC_SCALE               0xac

libavcodec/arm/mpegvideo_arm.c

@@ -18,6 +18,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include "libavutil/internal.h"
 #include "libavutil/arm/cpu.h"
 #include "libavcodec/avcodec.h"
 #include "libavcodec/mpegvideo.h"
@@ -25,12 +26,13 @@
 #include "asm-offsets.h"
 
 #if HAVE_NEON
-CHK_OFFS(MpegEncContext, y_dc_scale,       Y_DC_SCALE);
-CHK_OFFS(MpegEncContext, c_dc_scale,       C_DC_SCALE);
-CHK_OFFS(MpegEncContext, ac_pred,          AC_PRED);
-CHK_OFFS(MpegEncContext, block_last_index, BLOCK_LAST_INDEX);
-CHK_OFFS(MpegEncContext, inter_scantable.raster_end, INTER_SCANTAB_RASTER_END);
-CHK_OFFS(MpegEncContext, h263_aic,         H263_AIC);
+AV_CHECK_OFFSET(MpegEncContext, y_dc_scale,       Y_DC_SCALE);
+AV_CHECK_OFFSET(MpegEncContext, c_dc_scale,       C_DC_SCALE);
+AV_CHECK_OFFSET(MpegEncContext, ac_pred,          AC_PRED);
+AV_CHECK_OFFSET(MpegEncContext, block_last_index, BLOCK_LAST_INDEX);
+AV_CHECK_OFFSET(MpegEncContext, inter_scantable.raster_end,
+                INTER_SCANTAB_RASTER_END);
+AV_CHECK_OFFSET(MpegEncContext, h263_aic,         H263_AIC);
 #endif
 
 void ff_dct_unquantize_h263_inter_neon(MpegEncContext *s, int16_t *block,

libavutil/internal.h

@@ -84,6 +84,13 @@
 // to be forced to tokenize __VA_ARGS__
 #define E1(x) x
 
+/* Check if the hard coded offset of a struct member still matches reality.
+ * Induce a compilation failure if not.
+ */
+#define AV_CHECK_OFFSET(s, m, o) struct check_##o {    \
+        int x_##o[offsetof(s, m) == o? 1: -1];         \
+    }
+
 #define LOCAL_ALIGNED_A(a, t, v, s, o, ...)             \
     uint8_t la_##v[sizeof(t s o) + (a)];                \
     t (*v) o = (void *)FFALIGN((uintptr_t)la_##v, a)