交叉编译libwebsocket

1.下载libwebsockets
下载地址：git clone https://github.com/warmcat/libwebsockets.git

2.修改CMakeLists.txt

cd libwebsockets-main
vim CMakeLists.txt

添加下面内容

SET(CMAKE_SYSTEM_NAME Linux)
SET(TOOLCHAIN_DIR "/opt/myir-imx-fb/4.1.15-2.0.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi")

SET(CMAKE_FIND_ROOT_PATH "${TOOLCHAIN_DIR}")
SET(CMAKE_C_COMPILER "/opt/myir-imx-fb/4.1.15-2.0.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc")
SET(CMAKE_CXX_COMPILER "/opt/myir-imx-fb/4.1.15-2.0.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++")

set(MYSYSROOT /opt/myir-imx-fb/4.1.15-2.0.1/sysroots/cortexa7hf-neon-poky-linux-gnueabi)

# compiler/linker flags
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -march=armv7ve -marm -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=${MYSYSROOT}" CACHE INTERNAL "" FORCE)
set(CMAKE_C_LINK_FLAGS "${CMAKE_C_LINK_FLAGS} -march=armv7ve -marm -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=${MYSYSROOT}" CACHE INTERNAL "" FORCE)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} --sysroot=${MYSYSROOT}" CACHE INTERNAL "" FORCE)
set(CMAKE_CXX_LINK_FLAGS "${CMAKE_CXX_LINK_FLAGS} --sysroot=${MYSYSROOT}" CACHE INTERNAL "" FORCE)

set(CMAKE_FIND_ROOT_PATH "${MYSYSROOT}")

SET(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
#for libraries and headers in the target directories
SET(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
SET(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
SET(CMAKE_C_FLAGS"${CMAKE_C_FLAGS} --sysroot=/opt/myir-imx-fb/4.1.15-2.0.1/sysroots/cortexa7hf-neon-poky-linux-gnueabi")
SET(CMAKE_CXX_FLAGS"${CMAKE_CXX_FLAGS} --sysroot=/opt/myir-imx-fb/4.1.15-2.0.1/sysroots/cortexa7hf-neon-poky-linux-gnueabi")

#set(CMAKE_TRY_COMPILE_TARGET_TYPE "STATIC_LIBRARY")
SET(CMAKE_C_COMPILER_WORKS TRUE)

SET(CMAKE_CXX_COMPILER_WORKS TRUE)

注解一：添加这两行作用：直接跳过所有编译器检查， cmake会尝试编译静态库而不是可执行文件，用于交叉编译。

SET(CMAKE_C_COMPILER_WORKS TRUE）
SET(CMAKE_CXX_COMPILER_WORKS TRUE)

或者你可以设置使用这个来代替(直接跳过编译可执行程序）

SET(CMAKE_TRY_COMPILE_TARGET_TYPE "STATIC_LIBRARY")

如果不添加，执行第三步操作：cmake … 报下面错误

-- The CXX compiler identification is GNU 5.3.0
-- Check for working CXX compiler: /opt/myir-imx-fb/4.1.15-2.0.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++
-- Check for working CXX compiler: /opt/myir-imx-fb/4.1.15-2.0.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++ -- broken
CMake Error at /usr/share/cmake-3.10/Modules/CMakeTestCXXCompiler.cmake:45 (message):
  The C++ compiler
    "/opt/myir-imx-fb/4.1.15-2.0.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++"
  is not able to compile a simple test program.
  It fails with the following output:
    Change Dir: /home/用户名/Documents/libwebsockets-main/build/CMakeFiles/CMakeTmp
    Run Build Command:"/usr/bin/make" "cmTC_98ac0/fast"
    /usr/bin/make -f CMakeFiles/cmTC_98ac0.dir/build.make CMakeFiles/cmTC_98ac0.dir/build
    make[1]: Entering directory '/home/用户名/Documents/libwebsockets-main/build/CMakeFiles/CMakeTmp'
    Building CXX object CMakeFiles/cmTC_98ac0.dir/testCXXCompiler.cxx.o
    /opt/myir-imx-fb/4.1.15-2.0.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++    --sysroot=/opt/myir-imx-fb/4.1.15-2.0.1/sysroots/cortexa7hf-neon-poky-linux-gnueabi    -o CMakeFiles/cmTC_98ac0.dir/testCXXCompiler.cxx.o -c /home/用户名/Documents/libwebsockets-main/build/CMakeFiles/CMakeTmp/testCXXCompiler.cxx
    Linking CXX executable cmTC_98ac0
    /usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_98ac0.dir/link.txt --verbose=1
    /opt/myir-imx-fb/4.1.15-2.0.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++   --sysroot=/opt/myir-imx-fb/4.1.15-2.0.1/sysroots/cortexa7hf-neon-poky-linux-gnueabi -rdynamic CMakeFiles/cmTC_98ac0.dir/testCXXCompiler.cxx.o  -o cmTC_98ac0
    /opt/myir-imx-fb/4.1.15-2.0.1/sysroots/x86_64-pokysdk-linux/usr/libexec/arm-poky-linux-gnueabi/gcc/arm-poky-linux-gnueabi/5.3.0/real-ld: error: cmTC_98ac0 uses VFP register arguments, CMakeFiles/cmTC_98ac0.dir/testCXXCompiler.cxx.o does not
    /opt/myir-imx-fb/4.1.15-2.0.1/sysroots/x86_64-pokysdk-linux/usr/libexec/arm-poky-linux-gnueabi/gcc/arm-poky-linux-gnueabi/5.3.0/real-ld: failed to merge target specific data of file CMakeFiles/cmTC_98ac0.dir/testCXXCompiler.cxx.o
    collect2: error: ld returned 1 exit status
    CMakeFiles/cmTC_98ac0.dir/build.make:97: recipe for target 'cmTC_98ac0' failed
    make[1]: *** [cmTC_98ac0] Error 1
    make[1]: Leaving directory '/home/用户名/Documents/libwebsockets-main/build/CMakeFiles/CMakeTmp'
    Makefile:126: recipe for target 'cmTC_98ac0/fast' failed
    make: *** [cmTC_98ac0/fast] Error 2
  CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
  minimal-examples-lowlevel/api-tests/api-test-jrpc/CMakeLists.txt:1 (project)
-- Configuring incomplete, errors occurred!

注解二：设置CMAKE_C_FLAGS和CMAKE_CXX_FLAGS 一定要添加 -march=armv7ve -marm -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=${MYSYSROOT}如果不添加，出现下面错误

In file included from /opt/myir-imx-fb/4.1.15-2.0.1/sysroots/cortexa7hf-neon-poky-linux-gnueabi/usr/include/features.h:392:0,
                 from /opt/myir-imx-fb/4.1.15-2.0.1/sysroots/cortexa7hf-neon-poky-linux-gnueabi/usr/include/stdio.h:27,
                 from /home/用户名/Documents/libwebsockets-main/lib/core/./private-lib-core.h:53,
                 from /home/用户名/Documents/libwebsockets-main/lib/plat/unix/unix-caps.c:28:
/opt/myir-imx-fb/4.1.15-2.0.1/sysroots/cortexa7hf-neon-poky-linux-gnueabi/usr/include/gnu/stubs.h:7:29: fatal error: gnu/stubs-soft.h: No such file or directory
compilation terminated.
lib/CMakeFiles/websockets_shared.dir/build.make:62: recipe for target 'lib/CMakeFiles/websockets_shared.dir/plat/unix/unix-caps.c.o' failed
make[2]: *** [lib/CMakeFiles/websockets_shared.dir/plat/unix/unix-caps.c.o] Error 1
CMakeFiles/Makefile2:1076: recipe for target 'lib/CMakeFiles/websockets_shared.dir/all' failed
make[1]: *** [lib/CMakeFiles/websockets_shared.dir/all] Error 2
Makefile:162: recipe for target 'all' failed
make: *** [all] Error 2

-mfloat-abi=hard：使用硬浮点，交叉编译器没有软浮点对应的头文件,只有硬浮点对应的头文件
gnu/stubs.h内容：

vim ./4.1.15-2.0.1/sysroots/cortexa7hf-neon-poky-linux-gnueabi/usr/include/gnu/stubs.h

#if !defined __ARM_PCS_VFP
# include <gnu/stubs-soft.h>
#endif
#if defined __ARM_PCS_VFP
# include <gnu/stubs-hard.h>
#endif

可以找到<gnu/stubs-hard.h>

$ find . -name stubs-hard.h
./4.1.15-2.0.1/sysroots/cortexa7hf-neon-poky-linux-gnueabi/usr/include/gnu/stubs-hard.h

3.编译

mkdir build
cd build
cmake .. -DCMAKE_INSTALL_PREFIX=/home/用户名/arm/libwebsockets \
-DCMAKE_SYSTEM_NAME=Linux \
make -j8 && make install

到此编译结束了！！！