CMAKE missing sysroot when cross compiling

Question

I am having some troubles setting up cross compiling with CMAKE. The toolchain I am using is created in yocto which works perfectly outside of cmake.

I have followed a tutorial to setup the following toolchain file:

SET(CMAKE_SYSTEM_NAME Linux)
SET(CMAKE_SYSTEM_VERSION 1)
SET(CMAKE_SYSTEM_PROCESSOR arm)

# specify the cross compiler
SET(tools /opt/poky/1.7.1/sysroots/x86_64-pokysdk-linux/usr)
SET(CMAKE_C_COMPILER ${tools}/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc)
SET(CMAKE_CXX_COMPILER ${tools}/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc)

# set sysroot
SET(CMAKE_SYSROOT /home/sifu/test-yocto/qemuarmdfs)
#SET(CMAKE_FIND_ROOT_PATH /home/sifu/test-yocto/qemuarm)

# search for programs in the build host directories
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_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

And get the following error when running cmake

The C compiler
"/opt/poky/1.7.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc"
is not able to compile a simple test program.

It fails with the following output:

Change Dir: /home/sifu/Projects/mv/doublepump-single-pump-sw.ss016m21_swapp/cc/CMakeFiles/CMakeTmp

Run Build Command:/usr/bin/make "cmTryCompileExec4012536451/fast"

/usr/bin/make -f CMakeFiles/cmTryCompileExec4012536451.dir/build.make
CMakeFiles/cmTryCompileExec4012536451.dir/build

make[1]: Entering directory
`/home/sifu/Projects/mv/doublepump-single-pump-sw.ss016m21_swapp/cc/CMakeFiles/CMakeTmp'

/usr/bin/cmake -E cmake_progress_report
/home/sifu/Projects/mv/doublepump-single-pump-sw.ss016m21_swapp/cc/CMakeFiles/CMakeTmp/CMakeFiles
1

Building C object
CMakeFiles/cmTryCompileExec4012536451.dir/testCCompiler.c.o


/opt/poky/1.7.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc
-O2 -pipe -g -feliminate-unused-debug-types -o
CMakeFiles/cmTryCompileExec4012536451.dir/testCCompiler.c.o -c
/home/sifu/Projects/mv/doublepump-single-pump-sw.ss016m21_swapp/cc/CMakeFiles/CMakeTmp/testCCompiler.c

Linking C executable cmTryCompileExec4012536451

/usr/bin/cmake -E cmake_link_script
CMakeFiles/cmTryCompileExec4012536451.dir/link.txt --verbose=1

/opt/poky/1.7.1/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc
-O2 -pipe -g -feliminate-unused-debug-types -Wl,-O1 -Wl,--hash-style=gnu
-Wl,--as-needed CMakeFiles/cmTryCompileExec4012536451.dir/testCCompiler.c.o
-o cmTryCompileExec4012536451 -rdynamic

... (A lot of ld errors similar to the one below)

/opt/poky/1.7.1/sysroots/x86_64-pokysdk-linux/usr/libexec/arm-poky-linux-gnueabi/gcc/arm-poky-linux-gnueabi/4.9.1/ld:
cannot find crtn.o: No such file or directory

collect2: error: ld returned 1 exit status

make[1]: Leaving directory
`/home/sifu/Projects/mv/doublepump-single-pump-sw.ss016m21_swapp/cc/CMakeFiles/CMakeTmp'

If I manually run the gcc command described in the log above with --sysroot=/home/sifu/test-yocto/qemuarmdfs it works for me. Why isn't cmake using the sysroot flag when the path to sysroot is added in the toolchain file.

Answer 1

I have two solutions of this problem:

1. I use the following code in the toolchain file:

   # compiler
   set(CMAKE_C_COMPILER /path/to/arm-none-linux-gnueabi-gcc)
   set(CMAKE_CXX_COMPILER /path/to/arm-none-linux-gnueabi-g++)
   # sysroot location
   set(MYSYSROOT /path/to/sysroots/cortexa7-vfp-neon-telechips-linux-gnueabi)
   # compiler/linker flags
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} --sysroot=${MYSYSROOT}" CACHE INTERNAL "" FORCE)
   set(CMAKE_C_LINK_FLAGS "${CMAKE_C_LINK_FLAGS} --sysroot=${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)
   # cmake built-in settings to use find_xxx() functions
   set(CMAKE_FIND_ROOT_PATH "${MYSYSROOT}")
   set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
   set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
   set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
   

2. Second solution is to use CMakeForceCompiler package in the toolchain file. It looks differently but I have the same result:

   # compiler
   include(CMakeForceCompiler)
   cmake_force_c_compiler(/path/to/arm-none-linux-gnueabi-gcc GNU)
   cmake_force_cxx_compiler(/path/to/arm-none-linux-gnueabi-g++ GNU)
   # sysroot location
   set(MYSYSROOT /path/to/sysroots/cortexa7-vfp-neon-telechips-linux-gnueabi)
   # compiler/linker flags
   add_definitions("--sysroot=${MYSYSROOT}")
   set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} --sysroot=${MYSYSROOT}" CACHE INTERNAL "" FORCE)
   set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} --sysroot=${MYSYSROOT}" CACHE INTERNAL "" FORCE)
   # cmake built-in settings to use find_xxx() functions
   set(CMAKE_FIND_ROOT_PATH ${MYSYSROOT})
   set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
   set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
   set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
   

BTW, I can't use CMAKE_SYSROOT variable, since it available since CMake v3.0 only.