如何使用CMake编译RTT微内核

Rice加饭

发布于 2022-05-10 15:29:42

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发布于 2022-05-10 15:29:42

文章被收录于专栏：Rice嵌入式

已经大半个月没有更新文章了，大家还记得之前作者写的一篇关于RT-Thread的微内核移植的文章吗？如果不记得没关系。看如下是文章链接。

《如何移植RTT微内核到树莓派3B》

目前RTT微内核是RTT提供的体验版本。它采用了scons构建。作者也是刚接触scons，不是很了解，在这不过多的说明。那么来谈谈为什么不使用scons，采用cmake编译。不是因为scons不好，而是之前作者在写关于cmake的文章中，熊大（RTT的创始人）看到，然后在交流中，熊大说可以采用cmake进行编译。所以我也是冒着尝试的想法，开始了使用cmake去构建微内核。下面几篇文章是关于CMake理论的文章。

在构建过程中，由于不是很熟悉整个构建流程，在熊大亲自指导下，让我清晰很多。非常感谢熊大的支持。

其实整个过程最麻烦的编译选项的问题，特别是最后链接部分，这也是我花费最长去研究的。接下来，说一说微内核初步版本（只单独编译一个application）。

整个CMakeLists.txt文件如下，下面对每一行进行说明：

cmake_minimum_required(VERSION 3.10)

set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_SYSTEM_PROCESSOR arm)

set(CONFIG_PREFIX "/opt/gcc-arm-none-eabi/bin/arm-none-eabi-")
set(CMAKE_C_COMPILER "${CONFIG_PREFIX}gcc")
set(CMAKE_CXX_COMPILER "${CONFIG_PREFIX}g++")
set(CMAKE_ASM_COMPILER "${CONFIG_PREFIX}gcc")
set(CMAKE_OBJCOPY "${CONFIG_PREFIX}objcopy")
set(CMAKE_C_AR "${CONFIG_PREFIX}ar")
set(CMAKE_SIZE "${CONFIG_PREFIX}size")

#Disable compiler checks
set(CMAKE_C_COMPILER_FORCED TRUE)
set(CMAKE_CXX_COMPILER_FORCED TRUE)

set(microkernel_sdk_dir "${CMAKE_SOURCE_DIR}/sdk")
set(microkernel_apps_dir "${CMAKE_SOURCE_DIR}/apps")

project(rtt_microkernel)

enable_language(C ASM)

add_definitions(
    "-D__ASSEMBLY__"
    "-DRT_USING_NEWLIB"
    "-DHAVE_CCONFIG_H"
    "-D__STDC_ISO_10646__=201206L"
    "-D_STDC_PREDEF_H"
)

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -march=armv7-a -marm -msoft-float -Werror -Wall -O0 -g -gdwarf-2 -n -pie -fpie -fPIC -fpic --static -nostdinc")

set(CMAKE_ASM_FLAGS "${CMAKE_ASM_FLAGS} -march=armv7-a -marm -msoft-float -x assembler-with-cpp -O0 -g -fPIC")

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=armv7-a -marm -msoft-float -Werror -Wall -Woverloaded-virtual -fno-exceptions -fno-rtti -O0 -g -gdwarf-2 -n -pie -fpie -fPIC -fpic --static -nostdinc")

set(CMAKE_EXE_LINKER_FLAGS  "-march=armv7-a -marm -msoft-float -nostartfiles -nostdlib -n -pie -fpie -fPIC -fpic -Wl,-pie")


set(microkernel_sdk_inc 
    "${CMAKE_SOURCE_DIR}"
    "${microkernel_sdk_dir}/crt/rt-thread/components/dfs"
    "${microkernel_sdk_dir}/crt/rt-thread/components/drivers"
    "${microkernel_sdk_dir}/crt/rt-thread/components/net"
    "${microkernel_sdk_dir}/crt/rt-thread/components/net/netdev"
    "${microkernel_sdk_dir}/crt/rt-thread/components/lwip-2.1.0"
    "${microkernel_sdk_dir}/crt/rt-thread/include"
    "${microkernel_sdk_dir}/crt/rt-thread/include/libc"
    "${microkernel_sdk_dir}/crt/gcc"
    "${microkernel_sdk_dir}/libc/include"  
)

set(microkernel_apps_inc 
    "${microkernel_apps_dir}/hello"
)

set(microkernel_sdk_src 
    "${microkernel_sdk_dir}/crt/cplusplus/cxx_crt.cpp"
    "${microkernel_sdk_dir}/crt/gcc/arch/arm/syscall.S"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_channel.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_completion.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_device.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_ipc.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_net.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_syscall.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_thread.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_timer.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/stub.c"
)

set(microkernel_apps_src 
    "${microkernel_apps_dir}/hello/main.c"
)

set(CMAKE_EXECUTABLE_SUFFIX ".elf")

add_executable(${PROJECT_NAME} ${microkernel_apps_src} ${microkernel_sdk_src})
target_include_directories(${PROJECT_NAME} PRIVATE ${microkernel_sdk_inc} ${microkernel_apps_inc})
target_link_libraries(${PROJECT_NAME}
    PRIVATE
    -Wl,--start-group
    "${CMAKE_SOURCE_DIR}/sdk/libc/lib/libc.a"
    "${CMAKE_SOURCE_DIR}/sdk/libc/lib/libm.a"
    "${CMAKE_SOURCE_DIR}/sdk/libc/lib/libcrt.a"
    "libgcc.a"
    -Wl,--end-group
    -T ${microkernel_sdk_dir}/crt/gcc/arch/arm/gcc_arm.ld
)

1.检查cmake的版本

cmake_minimum_required(VERSION 3.10)

2.其中

CMAKE_SYSTEM_NAME：这个变量被设置，cmake才认为采用交叉编译，CMAKE_SYSTEM_NAME即目标机target所在的操作系统名称，比如ARM或者Linux你就需要写”Linux”,如果Android平台你就写”Android”,如果你的嵌入式平台没有相关OS你即需要写成”Generic”。

CMAKE_SYSTEM_PROCESSOR：代表目标系统的硬件或者CPU的型号，例如ARM、X86。

set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_SYSTEM_PROCESSOR arm)

3.关闭编译检测

set(CMAKE_C_COMPILER_FORCED TRUE)
set(CMAKE_CXX_COMPILER_FORCED TRUE)

4.定义sdk和apps两个目录变量。

set(microkernel_sdk_dir "${CMAKE_SOURCE_DIR}/sdk")
set(microkernel_apps_dir "${CMAKE_SOURCE_DIR}/apps")

5.定义项目的名字。

project(rtt_microkernel)

6.使能可以支持的语言，这里使能C语言和汇编语言。如果不是能，则相关文件不会进行编译。

enable_language(C ASM)

7.添加宏，即打开源文件的某项宏定义

add_definitions(
    "-D__ASSEMBLY__"
    "-DRT_USING_NEWLIB"
    "-DHAVE_CCONFIG_H"
    "-D__STDC_ISO_10646__=201206L"
    "-D_STDC_PREDEF_H"
)

8.添加编译选项，由于不同源文件添加的编译选项的不同，所以需要分别添加（分别是：C，汇编，C++, 链接），分别如下：

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -march=armv7-a -marm -msoft-float -Werror -Wall -O0 -g -gdwarf-2 -n -pie -fpie -fPIC -fpic --static -nostdinc")

set(CMAKE_ASM_FLAGS "${CMAKE_ASM_FLAGS} -march=armv7-a -marm -msoft-float -x assembler-with-cpp -O0 -g -fPIC")

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=armv7-a -marm -msoft-float -Werror -Wall -Woverloaded-virtual -fno-exceptions -fno-rtti -O0 -g -gdwarf-2 -n -pie -fpie -fPIC -fpic --static -nostdinc")

set(CMAKE_EXE_LINKER_FLAGS  "-march=armv7-a -marm -msoft-float -nostartfiles -nostdlib -n -pie -fpie -fPIC -fpic -Wl,-pie")

如何看我们添加的编译选项是否正确。我们编译采用外部编译，在build目录执行（cmake ..），然后查看flags.make文件。

flags.make文件的内容如下（包含相关语言的编译选项，宏定义，相关头文件路径）：我们通过这个文件查看是否正确：

9.定义两个头文件变量，分别是sdk头文件目录和apps头文件目录：

set(microkernel_sdk_inc 
    "${CMAKE_SOURCE_DIR}"
    "${microkernel_sdk_dir}/crt/rt-thread/components/dfs"
    "${microkernel_sdk_dir}/crt/rt-thread/components/drivers"
    "${microkernel_sdk_dir}/crt/rt-thread/components/net"
    "${microkernel_sdk_dir}/crt/rt-thread/components/net/netdev"
    "${microkernel_sdk_dir}/crt/rt-thread/components/lwip-2.1.0"
    "${microkernel_sdk_dir}/crt/rt-thread/include"
    "${microkernel_sdk_dir}/crt/rt-thread/include/libc"
    "${microkernel_sdk_dir}/crt/gcc"
    "${microkernel_sdk_dir}/libc/include"  
)

set(microkernel_apps_inc 
    "${microkernel_apps_dir}/hello"
)

10.定义两个源文件变量，分别是sdk源文件和apps源文件：

set(microkernel_sdk_src 
    "${microkernel_sdk_dir}/crt/cplusplus/cxx_crt.cpp"
    "${microkernel_sdk_dir}/crt/gcc/arch/arm/syscall.S"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_channel.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_completion.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_device.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_ipc.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_net.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_syscall.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_thread.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/rt_timer.c"
    "${microkernel_sdk_dir}/crt/rt-thread/src/stub.c"
)

set(microkernel_apps_src 
    "${microkernel_apps_dir}/hello/main.c"
)

11.定义可执行文件的后缀。

set(CMAKE_EXECUTABLE_SUFFIX ".elf")

12.根据源文件，添加一个可执行文件。

add_executable(${PROJECT_NAME} ${microkernel_apps_src} ${microkernel_sdk_src})

13.添加目标所依赖的头文件目录

target_include_directories(${PROJECT_NAME} PRIVATE ${microkernel_sdk_inc} ${microkernel_apps_inc})

14.添加目标依赖的链接库。以及链接脚本。

target_link_libraries(${PROJECT_NAME}
    PRIVATE
    -Wl,--start-group
    "${CMAKE_SOURCE_DIR}/sdk/libc/lib/libc.a"
    "${CMAKE_SOURCE_DIR}/sdk/libc/lib/libm.a"
    "${CMAKE_SOURCE_DIR}/sdk/libc/lib/libcrt.a"
    "libgcc.a"
    -Wl,--end-group
    -T ${microkernel_sdk_dir}/crt/gcc/arch/arm/gcc_arm.ld
)

15.最后链接生成可执行文件的命令是否正确，我们可以查看link.txt文件。