Build error caused by missing library arc4random

Question

I'm currently working on a Streaming framework, and decided to use ffmpeg to encode and or decode my Video and or Audio.

So i clicked through https://ffmpeg.org for the api files, and downloaded the statically linked version only to find out it actually contained a .exe (I use Windows in development, but plan on using Linux in production) instead of one or more dll's and header informations.

Since i don't think i can use the 'exe' as replacement for an dll, i cloned the git source, and tried to compile it myself.

Then, while compiling i run into this error:

CC  libavutil/random_seed.o
libavutil/random_seed.c: In function 'av_get_random_seed':
libavutil/random_seed.c:130:12: error: implicit declaration of function 'arc4random' [-Werror=implicit-function-declaration]
     return arc4random();
            ^
cc1: some warnings being treated as errors
common.mak:60: recipe for target 'libavutil/random_seed.o' failed
make: *** [libavutil/random_seed.o] Error 1

As far as I can tell, this means that I'm missing the library arc4random, so I started searching for this lib, and found absolutly nothing, besides the fact that this library is somehow Apple related..., but no dll's and stuff or sources to compile it myself.

I use cygwin and its GCC to compile on 64-Bit windows 7 Machine.

Can anyone hint me to some location where I can get this missing library, or some other possibility to get ffmpeg as library into my project? (I would prefer something I can link statically , since this project is meant to be a lib by itself)

Maybe is there a way I can make use of that downloaded exe of ffmpeg, since i can borrow its headers from the source I cloned from Git?

Any Hint appreciated.

Best Regards,

Jannik Adam

Answer 1

This seems to be caused because the #if is incorrectly reporting that the system has this function. I was able to get around it by editing a couple of files.

Open libavutil/random_seed.c and look for #if HAVE_ARC4RANDOM, should be around line 129, and remove that block of three lines:

129 #if HAVE_ARC4RANDOM
130     return arc4random();
131 #endif

When you run make again you'll probably get another similar failure in time.c for gettimeofday(), so open libavutil/time.c and look for #if HAVE_GETTIMEOFDAY which should be around line 41 and remove the first block there, like this:

Before changing:

41 #if HAVE_GETTIMEOFDAY
42     struct timeval tv;
43     gettimeofday(&tv, NULL);
44     return (int64_t)tv.tv_sec * 1000000 + tv.tv_usec;
45 #elif HAVE_GETSYSTEMTIMEASFILETIME

After changing:

41 #if HAVE_GETSYSTEMTIMEASFILETIME

After those two changes the compile got a lot further but failed on ffserver.c:

ffserver.c: In function ‘main’:
ffserver.c:4000:5: error: implicit declaration of function ‘sigaction’ [-Werror=implicit-function-declaration]
     sigaction(SIGCHLD, &sigact, 0);

To fix this error I opened config.mak and added -D_XOPEN_SOURCE=700 to the end of CFLAGS, like this:

42 CFLAGS=   -std=c99 -fomit-frame-pointer -pthread  -g -Wdeclaration-after-statement -Wall -Wdisabled-optimization -Wpointer-arith -Wredundant-decls -Wwrite-strings -Wtype-limits -Wundef -Wmissing-prototypes -Wno-pointer-to-int-cast -Wstrict-prototypes -Wempty-body -Wno-parentheses -Wno-switch -Wno-format-zero-length -Wno-pointer-sign -O3 -fno-math-errno -fno-signed-zeros -Werror=format-security -Werror=implicit-function-declaration -Werror=missing-prototypes -Werror=return-type -Werror=vla -Wformat -fdiagnostics-color=auto -Wno-maybe-uninitialized -D_XOPEN_SOURCE=700

This post explains a bit about why -D_XOPEN_SOURCE=700 helps.

Then I ran make again and it finally succeeded. After running make install all the binaries were put in place and I was able to successfully use it!