build FFmpeg with LLVm 12

Hello, I am using Clang 12 on my macOS:

clang --version
clang version 12.0.0
Target: x86_64-apple-darwin19.6.0
Thread model: posix
InstalledDir: /usr/local/opt/llvm/bin

I need to use your project on FFmpeg so I used these commands:

brew install automake fdk-aac git lame libass libtool libvorbis libvpx  opus sdl shtool texi2html theora wget x264 x265 xvid nasm
export LLVM_COMPILER=clang
export LLVM_BITCODE_GENERATION_FLAGS='-g'
mkdir build
cd build
CC=wllvm CXX=wllvm++ /Users/macbook/Documents/github-repos/FFmpeg/configure  --prefix=/usr/local --enable-gpl --enable-nonfree --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame  --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libopus --enable-libxvid --samples=fate-suite/

extract-bc ffmpeg

but it shows this:

ERROR:FFmpeg/build/ffmpeg contained no __WLLVM segment

Can you please help me? Thank you

[tylzh97]

FFmpeg‘s configure file does not using system variable “CC”. If you want to using wllvm to build it , you shuold do someting like that: ./configure --disable-yasm --cc=wllvm and then you can extract it with extract-bc ffmpeg

full commands here:

cd ffmpeg
./configure --disable-yasm --cc=wllvm
make
extract-bc ffmpeg

and you can find ffmpeg.bc here!

[ianamason]

So all I can suggest is to turn on logging and watch what is happening. These sorts of things are possible:

1 The build system is using lto and so the .o files are actually bitcode.

2 The build system has hard coded the compiler.

Some detective work is required. File an issue, solve it, then bask in the fame 😜