Complex Cross compiling example
Here are step by step instructions for cross-building the external projects needed for lws with lwsws + mbedtls as an example.
In the example, my toolchain lives in <tool_chain_file>/compile_tools/toolchain-aarch64_armv8-a_gcc-4.8-linaro_glibc-2.19 and is named arm-openwrt-linux-muslgnueabi. So you will need to adapt those to where your toolchain lives and its name where you see them here.
Likewise I do all this in /tmp but it has no special meaning, you can adapt that to somewhere else.
All "foreign" cross-built binaries are sent into /tmp/cross so they cannot be confused for 'native' x86_64 stuff on your host machine in /usr/[local/]....
Prepare the cmake toolchain file
1) cd /tmp
2) wget -O mytoolchainfile https://raw.githubusercontent.com/warmcat/libwebsockets/master/contrib/cross-arm-linux-gnueabihf.cmake
3) Edit /tmp/mytoolchainfile adapting CROSS_PATH, CMAKE_C_COMPILER and CMAKE_CXX_COMPILER to reflect your toolchain install dir and path to your toolchain C and C++ compilers respectively. For my case:
set(CROSS_PATH <tool_chain_file>/compile_tools/toolchain-aarch64_armv8-a_gcc-4.8-linaro_glibc-2.19/)
set(CMAKE_C_COMPILER "${CROSS_PATH}/bin/arm-openwrt-linux-muslgnueabi-gcc")
set(CMAKE_CXX_COMPILER "${CROSS_PATH}/bin/arm-openwrt-linux-muslgnueabi-g++")
libsockets:::
cmake .. -DCMAKE_INSTALL_PREFIX:PATH=<tool_chain_file>/compile_tools/toolchain-aarch64_armv8-a_gcc-4.8-linaro_glibc-2.19 \
-DCMAKE_TOOLCHAIN_FILE=../cross-arm-linux-gnueabihf.cmake \
-DLWS_WITHOUT_EXTENSIONS=1 -DLWS_WITH_SSL=0 \
-DLWS_WITH_ZIP_FOPS=0 -DLWS_WITH_ZLIB=0
lib/libmbedtls:::
cmake .. -DCMAKE_TOOLCHAIN_FILE=../cross-arm-linux-gnueabihf.cmake -DCMAKE_INSTALL_PREFIX:PATH=<tool_chain_file>/compile_tools/toolchain-aarch64_armv8-a_gcc-4.8-linaro_glibc-2.19 -DCMAKE_BUILD_TYPE=RELEASE -DUSE_SHARED_MBEDTLS_LIBRARY=1
libsockets:::
cmake .. -DCMAKE_TOOLCHAIN_FILE=<tool_chain_file>/compile_tools/toolchain-aarch64_armv8-a_gcc-4.8-linaro_glibc-2.19 \
-DCMAKE_INSTALL_PREFIX:PATH=<tool_chain_file>/compile_tools/toolchain-aarch64_armv8-a_gcc-4.8-linaro_glibc-2.19 \
-DLWS_WITH_LWSWS=1 \
-DLWS_WITH_MBEDTLS=1 \
-DLWS_MBEDTLS_LIBRARIES="../../mbedtls-2.11.0/build/library/libmbedtls.so" \
-DLWS_MBEDTLS_INCLUDE_DIRS=../../mbedtls-2.11.0/include/mbedtls \
1/4: Building libuv cross:
1) export PATH=<tool_chain_file>/compile_tools/toolchain-aarch64_armv8-a_gcc-4.8-linaro_glibc-2.19/bin:$PATH
2) cd /tmp
###mkdir cross we will put the cross-built libs in /tmp/cross
3) git clone https://github.com/libuv/libuv.git ##get libuv
4) cd libuv
5) ./autogen.sh
6) ./configure --host=aarch64-openwrt-linux-gnu --prefix=/tmp/cross
7) make && make install this will install to /tmp/cross/...
8) file /tmp/cross/lib/libuv.so.1.0.0 Check it's really built for ARM
/tmp/cross/lib/libuv.so.1.0.0: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamically linked, not stripped
2/4: Building zlib cross
1) cd /tmp
2) git clone https://github.com/madler/zlib.git
3) cd /tmp/zlib
4) CC=aarch64-openwrt-linux-gnu-gcc ./configure --prefix=/tmp/cross
5) make && make install
6) file /tmp/cross/lib/libz.so.1.2.11 This is just to confirm we built an ARM lib as expected
/tmp/cross/lib/libz.so.1.2.11: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamically linked, not stripped
3/4: Building mbedtls cross
1) cd /tmp
2) git clone https://github.com/ARMmbed/mbedtls.git
3) cd mbedtls ; mkdir build ; cd build
3) cmake .. -DCMAKE_TOOLCHAIN_FILE=../cross-arm-linux-gnueabihf.cmake -DCMAKE_INSTALL_PREFIX:PATH=/tmp/cross -DCMAKE_BUILD_TYPE=RELEASE -DUSE_SHARED_MBEDTLS_LIBRARY=1
## mbedtls also uses cmake, so you can simply reuse the toolchain file you used for libwebsockets. That is why you shouldn't put project-specific options in the toolchain file, it should just describe the toolchain.
4) make && make install
5) file /tmp/cross/lib/libmbedcrypto.so.2.6.0
/tmp/cross/lib/libmbedcrypto.so.2.13.1: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamically linked, not stripped
4/4: Building libwebsockets with everything
1) cd /tmp
2) git clone ssh://git@github.com/warmcat/libwebsockets
3) cd libwebsockets ; mkdir build ; cd build
4) (this is all one line on the commandline)
cmake .. -DCMAKE_TOOLCHAIN_FILE=../cross-arm-linux-gnueabihf.cmake \
-DCMAKE_INSTALL_PREFIX:PATH=/tmp/cross \
-DLWS_WITH_LWSWS=1 \
-DLWS_WITH_MBEDTLS=1 \
-DLWS_MBEDTLS_LIBRARIES="/tmp/cross/lib/libmbedcrypto.so;/tmp/cross/lib/libmbedtls.so;/tmp/cross/lib/libmbedx509.so" \
-DLWS_MBEDTLS_INCLUDE_DIRS=/tmp/cross/include \
-DLWS_LIBUV_LIBRARIES=/tmp/cross/lib/libuv.so \
-DLWS_LIBUV_INCLUDE_DIRS=/tmp/cross/include \
-DLWS_ZLIB_LIBRARIES=/tmp/cross/lib/libz.so \
-DLWS_ZLIB_INCLUDE_DIRS=/tmp/cross/include
3) make && make install
4) file /tmp/cross/lib/libwebsockets.so
/tmp/cross/lib/libwebsockets.so: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamically linked, not stripped
5) aarch64-openwrt-linux-objdump -p /tmp/cross/lib/libwebsockets.so | grep NEEDED
## Confirm that the lws library was linked against everything we expect (libm / libc are provided by your toolchain)
NEEDED libmbedtls.so
NEEDED libuv.so.1
NEEDED libm.so.6
NEEDED libgcc_s.so.1
NEEDED libc.so.6
You will also find the lws test apps in /tmp/cross/bin... to run lws on the target you will need to copy the related things from /tmp/cross... all the .so from /tmp/cross/lib and anything from /tmp/cross/bin you want.
