How can i cross-compile for Raspberry Pi Zero with WSL?

Question

I am working on a project with the Raspberry Pi Zero and since I don't have a monitor to connect the Pi and don't want to use vi through ssh I thouhgt that cross compiling would be a decent solution. I am trying to do it in a Windows machine with WSL since almost all the guides I found use Linux.

For my project I need to use the bcm2835 library for managing the GPIOs of the Pi.

I found this guide which tells me how to build a library for cross compilation: https://medium.com/@au42/the-useful-raspberrypi-cross-compile-guide-ea56054de187 When I run cmake to build the shared library I have this out put.

    mariano@MSI:~/raspberrypi/bcm2835-1.68/src$ cmake . - DCMAKE_TOOLCHAIN_FILE=/home/mariano/raspberrypi/pi.cmake
CMake Warning (dev) in CMakeLists.txt:
  No project() command is present.  The top-level CMakeLists.txt file must
  contain a literal, direct call to the project() command.  Add a line of
  code such as

    project(ProjectName)

  near the top of the file, but after cmake_minimum_required().

  CMake is pretending there is a "project(Project)" command on the first
  line.
This warning is for project developers.  Use -Wno-dev to suppress it.

-- The C compiler identification is GNU 4.9.3
-- The CXX compiler identification is GNU 4.9.3
-- Check for working C compiler: /home/mariano/raspberrypi/tools/arm-bcm2708/arm-rpi-4.9.3-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc
-- Check for working C compiler: /home/mariano/raspberrypi/tools/arm-bcm2708/arm-rpi-4.9.3-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /home/mariano/raspberrypi/tools/arm-bcm2708/arm-rpi-4.9.3-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc
-- Check for working CXX compiler: /home/mariano/raspberrypi/tools/arm-bcm2708/arm-rpi-4.9.3-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - found
-- Found Threads: TRUE
-- Configuring done
-- Generating done
-- Build files have been written to: /home/mariano/raspberrypi/bcm2835-1.68/src

After that I run make an got this output:

mariano@MSI:~/raspberrypi/bcm2835-1.68/src$ make
Scanning dependencies of target bcm2528
[ 33%] Building C object CMakeFiles/bcm2528.dir/bcm2835.c.o
/home/mariano/raspberrypi/bcm2835-1.68/src/bcm2835.c: In function 'bcm2835_delay':
/home/mariano/raspberrypi/bcm2835-1.68/src/bcm2835.c:531:5: warning: implicit declaration of function 'nanosleep' [-Wimplicit-function-declaration]
     nanosleep(&sleeper, NULL);
     ^
/home/mariano/raspberrypi/bcm2835-1.68/src/bcm2835.c: In function 'malloc_aligned':
/home/mariano/raspberrypi/bcm2835-1.68/src/bcm2835.c:1754:5: warning: implicit declaration of function 'posix_memalign' [-Wimplicit-function-declaration]
     errno = posix_memalign(&mem, BCM2835_PAGE_SIZE, size);
     ^
[ 66%] Building C object CMakeFiles/bcm2528.dir/test.c.o
In file included from /home/mariano/raspberrypi/bcm2835-1.68/src/test.c:10:0:
/home/mariano/raspberrypi/bcm2835-1.68/src/bcm2835.h:692:8: error: unknown type name 'off_t'
 extern off_t bcm2835_peripherals_base;
        ^
make[2]: *** [CMakeFiles/bcm2528.dir/build.make:76: CMakeFiles/bcm2528.dir/test.c.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:76: CMakeFiles/bcm2528.dir/all] Error 2
make: *** [Makefile:84: all] Error 2

Checking the output of the cmake command found these lines

-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found

I googled it and tried a few solutions but they didn't work.

Is there something I am doing wrong? Also, if you have another method to cross compile tell me, I choose this one because it shows how to use other libraries other that ones that come in Raspbian.

Any help would be appreciated.

Answer 1

I remember doing a cross-compilation for ARM using Debian Cross Toolchains (right now I just compile directly on a Pi 4). Raspberry Pi OS is very close to Debian-armhf, so doing everything the Debian way typically has a higher chance of success than the alternatives.

Your immediate problem appears to be wrong version of the C library, libc. How did you install it? On Debian, you would get it with apt-get install crossbuild-essential-armhf, along with other essential packages you need for cross-compilation. If you somehow installed the WSL version, it's not at all surprising that POSIX threads are not working, since Windows is using a different threading model.

If you want to be pedantic, you could pull the actual Raspbian libraries and build against these: this would avoid the rare incompatibilities between RPi and Debian, should you ever run into these.

Answer 2

I modify "extern off_t bcm2835_peripherals_base;" to "extern uint32_t bcm2835_peripherals_base;" then it works for my Pi4.