'-Wl,--as-needed' breaks build

[Nikoli]

A lot if not all targets fail to build with '-Wl,--as-needed', without they build fine:

$ x86_64-pc-linux-gnu-gcc -march=corei7-avx -O2 -pipe -I/usr/include/mjpegtools -I/usr/include/freetype2 -D__STDC_CONSTANT_MACROS  -c -o libav-bitrate.o libav-bitrate.c
$ x86_64-pc-linux-gnu-gcc -march=corei7-avx -O2 -pipe -I/usr/include/mjpegtools -I/usr/include/freetype2 -D__STDC_CONSTANT_MACROS  -c -o progress.o progress.c
progress.c: In function ‘progress_loadBar’:
progress.c:129:2: warning: format ‘%lld’ expects argument of type ‘long long int’, but argument 3 has type ‘off_t’ [-Wformat]
$ x86_64-pc-linux-gnu-gcc -march=corei7-avx -O2 -pipe -Wl,--hash-style=gnu -Wl,-O1 -Wl,--as-needed -lswscale -lavcodec -lavformat -lavutil -o libav-bitrate libav-bitrate.o progress.o
libav-bitrate.o: In function `main':
libav-bitrate.c:(.text.startup+0x242): undefined reference to `av_register_all'
libav-bitrate.c:(.text.startup+0x269): undefined reference to `avformat_open_input'
libav-bitrate.c:(.text.startup+0x280): undefined reference to `avformat_find_stream_info'
libav-bitrate.c:(.text.startup+0x29d): undefined reference to `av_dump_format'
libav-bitrate.c:(.text.startup+0x3aa): undefined reference to `avcodec_find_decoder'
libav-bitrate.c:(.text.startup+0x412): undefined reference to `avcodec_open2'
libav-bitrate.c:(.text.startup+0x41f): undefined reference to `avcodec_alloc_frame'
libav-bitrate.c:(.text.startup+0x4b3): undefined reference to `av_free_packet'
libav-bitrate.c:(.text.startup+0x4c8): undefined reference to `av_read_frame'
libav-bitrate.c:(.text.startup+0x55b): undefined reference to `avcodec_decode_video2'
libav-bitrate.c:(.text.startup+0x70e): undefined reference to `av_free'
libav-bitrate.c:(.text.startup+0x718): undefined reference to `avcodec_close'
libav-bitrate.c:(.text.startup+0x725): undefined reference to `avformat_close_input'
collect2: error: ld returned 1 exit status
$ x86_64-pc-linux-gnu-gcc -march=corei7-avx -O2 -pipe -Wl,--hash-style=gnu -Wl,-O1 -lswscale -lavcodec -lavformat -lavutil -o libav-bitrate libav-bitrate.o progress.o

[Nikoli]

I have libav-9.10

[silicontrip]

My gcc doesn't like the --as-needed option. So I cannot test any fix.
It appears to be the order of the object files on the command line.
I've changed the Makefile for libav-bitrate. I won't change the others until you can confirm that this resolves the issue.

[Nikoli]

I confirm that moving *.o options before LDFLAGS solves problem:

$ x86_64-pc-linux-gnu-gcc -march=corei7-avx -O2 -pipe libav-bitrate.c progress.o -Wl,--hash-style=gnu -Wl,-O1 -Wl,--as-needed -lswscale -lavcodec -lavformat -lavutil -o libav-bitrate
$ objdump -p libav-bitrate|grep NEEDED|sort
  NEEDED               libavcodec.so.54
  NEEDED               libavformat.so.54
  NEEDED               libavutil.so.52
  NEEDED               libc.so.6

As you can see --as-needed works, it does not link to not used libswscale.
Your changes to Makefile are partly wrong, because placing --as-needed after -l* is no-op:

$ x86_64-pc-linux-gnu-gcc -march=corei7-avx -O2 -pipe libav-bitrate.c progress.o -lswscale -lavcodec -lavformat -lavutil -ljpeg -lfftw3 -lz -Wl,--hash-style=gnu -Wl,-O1 -Wl,--as-needed -o libav-bitrate
$ objdump -p libav-bitrate|grep NEEDED|sort
  NEEDED               libavcodec.so.54
  NEEDED               libavformat.so.54
  NEEDED               libavutil.so.52
  NEEDED               libc.so.6
  NEEDED               libfftw3.so.3
  NEEDED               libjpeg.so.8
  NEEDED               libswscale.so.2
  NEEDED               libz.so.1

[Nikoli]

Building with --as-needed detected 2 other bugs:

1. yuvilace does not need fftw
2. opencv related flags should be
   OPENCV_LIBS=-lopencv_core -lopencv_highgui -lopencv_imgproc

[Nikoli]

Updated my pull request, this is now fixed in #18

[silicontrip]

Hope this last Makefile change fixes these issues.

[Nikoli]

Works mostly fine now, but what about yuvilace.c? It does not link to fftw:

$ objdump -p yuvilace|grep NEEDED
  NEEDED               libmjpegutils-2.0.so.0
  NEEDED               libc.so.6

May be it is not used at all?

$ cat /tmp/cppcheck_lavtools.log|grep yuvilace
[yuvilace.c:91]: (style) The scope of the variable 't' can be reduced.
[yuvilace.c:349]: (style) The scope of the variable 'drop_frames' can be reduced.
[yuvilace.c:193]: (style) Unused variable: frame_data_size
[yuvilace.c:197]: (style) Variable 'l' is assigned a value that is never used.
[yuvilace.c:197]: (style) Variable 'f' is assigned a value that is never used.
[yuvilace.c:199]: (style) Variable 'points' is assigned a value that is never used.
[yuvilace.c:199]: (style) Variable 'window' is assigned a value that is never used.
[yuvilace.c:369]: (style) Variable 'drop_frames' is assigned a value that is never used.
[yuvilace.c:366]: (style) Variable 'src_interlacing' is assigned a value that is never used.
[yuvilace.c:396]: (style) Variable 'src_frame_rate' is assigned a value that is never used.

[silicontrip]

yuvilace was an experiment to detect interlacing using an fft. It was unable to fulfil it's original design, so is left in a half built state. I may've tried other methods of detecting interlacing, implemented in this code.