Cross Compiling

Issues:

need cross compile toolchain
- you need to find or build an entire toolchain environment; ubuntu has some, others have some, Crosstool-NG will build one from scratch
- for autotools, you typically need to define tools like ar, gcc, g++ in the build script
- for cmake, you typically need a toolchain file to specify details
need to cross compile any dependencies (static link what you can)

libz example

   echo Getting source code for libraries...
   if [ ! -d zlib ]; then
       wget http://zlib.net/zlib-${zlib_version}.tar.gz
       untar zlib-${zlib_version}.tar.gz
       ln -s zlib-${zlib_version} zlib
   fi
   echo Building libraries...
   if [ "$rebuild_libs" = true ]; then
   
       export cross=arm-linux-gnueabi-
   
       # ZLIB
       cd zlib
       ./configure --prefix=${install_root}
       make CC="${cross}gcc" AR="${cross}ar r" RANLIB="${cross}ranlib"
       make install
       cd ..
   fi

openssl example

   echo Getting source code for libraries...
   if [ ! -d openssl ]; then
       wget https://www.openssl.org/source/openssl-${openssl_version}.tar.gz
       untar openssl-${openssl_version}.tar.gz
       ln -s openssl-${openssl_version} openssl
   fi
   
   echo Building libraries...
   
   if [ "$rebuild_libs" = true ]; then
   
       export cross=arm-linux-gnueabi-
   
       # OPENSSL
       cd openssl
       ./Configure dist --prefix=${install_root} --openssldir=${install_root}
       make CC="${cross}gcc" AR="${cross}ar r" RANLIB="${cross}ranlib"
       make install
       cd ..
   fi

- libwebsockets example
need to match the libraries on target machine for any dynamic linking requirements
need to match the build to the target kernel (or you might get "kernel too old")