Add attribute that forces alignment of stack to functions that need it.

Necessary for systems that don't align by default to 16 bytes, required by some
SSE instructions.
Requires GCC >= 4.2.
Based on patch by Gaël Chardon.

Originally committed as revision 10106 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dsputil.c

@@ -3833,7 +3833,8 @@ int ff_check_alignment(void){
             av_log(NULL, AV_LOG_ERROR,
                 "Compiler did not align stack variables. Libavcodec has been miscompiled\n"
                 "and may be very slow or crash. This is not a bug in libavcodec,\n"
-                "but in the compiler. Do not report crashes to FFmpeg developers.\n");
+                "but in the compiler. You may try recompiling using gcc >= 4.2.\n"
+                "Do not report crashes to FFmpeg developers.\n");
 #endif
             did_fail=1;
         }

libavcodec/pthread.c

@@ -42,7 +42,7 @@ typedef struct ThreadContext {
     int done;
 } ThreadContext;
 
-static void* worker(void *v)
+static void* attribute_align_arg worker(void *v)
 {
     AVCodecContext *avctx = v;
     ThreadContext *c = avctx->thread_opaque;

libavcodec/utils.c

@@ -829,7 +829,7 @@ AVFrame *avcodec_alloc_frame(void){
     return pic;
 }
 
-int avcodec_open(AVCodecContext *avctx, AVCodec *codec)
+int attribute_align_arg avcodec_open(AVCodecContext *avctx, AVCodec *codec)
 {
     int ret= -1;
 
@@ -880,7 +880,7 @@ end:
     return ret;
 }
 
-int avcodec_encode_audio(AVCodecContext *avctx, uint8_t *buf, int buf_size,
+int attribute_align_arg avcodec_encode_audio(AVCodecContext *avctx, uint8_t *buf, int buf_size,
                          const short *samples)
 {
     if(buf_size < FF_MIN_BUFFER_SIZE && 0){
@@ -895,7 +895,7 @@ int avcodec_encode_audio(AVCodecContext *avctx, uint8_t *buf, int buf_size,
         return 0;
 }
 
-int avcodec_encode_video(AVCodecContext *avctx, uint8_t *buf, int buf_size,
+int attribute_align_arg avcodec_encode_video(AVCodecContext *avctx, uint8_t *buf, int buf_size,
                          const AVFrame *pict)
 {
     if(buf_size < FF_MIN_BUFFER_SIZE){
@@ -923,7 +923,7 @@ int avcodec_encode_subtitle(AVCodecContext *avctx, uint8_t *buf, int buf_size,
     return ret;
 }
 
-int avcodec_decode_video(AVCodecContext *avctx, AVFrame *picture,
+int attribute_align_arg avcodec_decode_video(AVCodecContext *avctx, AVFrame *picture,
                          int *got_picture_ptr,
                          uint8_t *buf, int buf_size)
 {
@@ -946,7 +946,7 @@ int avcodec_decode_video(AVCodecContext *avctx, AVFrame *picture,
     return ret;
 }
 
-int avcodec_decode_audio2(AVCodecContext *avctx, int16_t *samples,
+int attribute_align_arg avcodec_decode_audio2(AVCodecContext *avctx, int16_t *samples,
                          int *frame_size_ptr,
                          uint8_t *buf, int buf_size)
 {

libavcodec/w32thread.c

@@ -36,7 +36,7 @@ typedef struct ThreadContext{
 }ThreadContext;
 
 
-static unsigned __stdcall thread_func(void *v){
+static unsigned __stdcall attribute_align_arg thread_func(void *v){
     ThreadContext *c= v;
 
     for(;;){

libavutil/internal.h

@@ -34,6 +34,14 @@
 #include <stddef.h>
 #include <assert.h>
 
+#ifndef attribute_align_arg
+#if defined(__GNUC__) && (__GNUC__ > 4 || __GNUC__ == 4 && __GNUC_MINOR__>1)
+#    define attribute_align_arg __attribute__((force_align_arg_pointer))
+#else
+#    define attribute_align_arg
+#endif
+#endif
+
 #ifndef attribute_used
 #if defined(__GNUC__) && (__GNUC__ > 3 || __GNUC__ == 3 && __GNUC_MINOR__ > 0)
 #    define attribute_used __attribute__((used))