Assertion Failed: The toolchain is unable to build a dummy C file

Question

A number of students + myself have been attempting to set up a Zephyr RTOS build environment under Windows 10, to build applications that target various ARM Cortex M boards. We have each followed the Zephyr "Getting Started Guide" and ran into the same problem. When compiling for a number of different boards (let's just use the nrf52840dk_nrf52840 as an example here) we get this error:

Error Message

C:\Users\John\code\eip-zephyr>west build -p auto -b nrf52840dk_nrf52840 .\zephyr\samples\basic\blinky\
-- west build: generating a build system
Including boilerplate (Zephyr base): C:/Users/John/code/eip-zephyr/zephyr/cmake/app/boilerplate.cmake
-- Application: C:/Users/John/code/eip-zephyr/zephyr/samples/basic/blinky
-- Zephyr version: 2.4.0 (C:/Users/John/code/eip-zephyr/zephyr)
-- Found Python3: C:/Python39/python.exe (found suitable exact version "3.9.0") found components: Interpreter
-- Found west (found suitable version "0.8.0", minimum required is "0.7.1")
-- Board: nrf52840dk_nrf52840
-- Cache files will be written to: C:/Users/John/code/eip-zephyr/zephyr/.cache
-- Found toolchain: gnuarmemb (C:/gnu_arm_embedded)
-- Found BOARD.dts: C:/Users/John/code/eip-zephyr/zephyr/boards/arm/nrf52840dk_nrf52840/nrf52840dk_nrf52840.dts
-- Generated zephyr.dts: C:/Users/John/code/eip-zephyr/build/nrf52840dk_nrf52840/blinky/zephyr/zephyr.dts
-- Generated devicetree_unfixed.h: C:/Users/John/code/eip-zephyr/build/nrf52840dk_nrf52840/blinky/zephyr/include/generated/devicetree_unfixed.h
Parsing C:/Users/John/code/eip-zephyr/zephyr/Kconfig
Loaded configuration 'C:/Users/John/code/eip-zephyr/zephyr/boards/arm/nrf52840dk_nrf52840/nrf52840dk_nrf52840_defconfig'
Merged configuration 'C:/Users/John/code/eip-zephyr/zephyr/samples/basic/blinky/prj.conf'
Configuration saved to 'C:/Users/John/code/eip-zephyr/build/nrf52840dk_nrf52840/blinky/zephyr/.config'
Kconfig header saved to 'C:/Users/John/code/eip-zephyr/build/nrf52840dk_nrf52840/blinky/zephyr/include/generated/autoconf.h'
-- The C compiler identification is GNU 9.3.1
-- The CXX compiler identification is GNU 9.3.1
-- The ASM compiler identification is GNU
-- Found assembler: C:/gnu_arm_embedded/bin/arm-none-eabi-gcc.exe
CMake Error at ../../../cmake/extensions.cmake:1569 (message):
  Assertion failed: The toolchain is unable to build a dummy C file.  See
  CMakeError.log.
Call Stack (most recent call first):
  ../../../CMakeLists.txt:42 (assert)


-- Configuring incomplete, errors occurred!
See also "C:/Users/John/code/eip-zephyr/build/nrf52840dk_nrf52840/blinky/CMakeFiles/CMakeOutput.log".
See also "C:/Users/John/code/eip-zephyr/build/nrf52840dk_nrf52840/blinky/CMakeFiles/CMakeError.log".
FATAL ERROR: command exited with status 1: 'C:\Program Files\CMake\bin\cmake.EXE' '-DWEST_PYTHON=c:\python39\python.exe' '-BC:\Users\John\code\eip-zephyr\build\nrf52840dk_nrf52840\blinky' '-SC:\Users\John\code\eip-zephyr\zephyr\samples\basic\blinky' -GNinja -DBOARD=nrf52840dk_nrf52840

This error refers us to the files: CMakeError and CMakeOutput. Here are their contents below:

CMakeError

Compiling the C compiler identification source file "CMakeCCompilerId.c" failed.
Compiler: C:/gnu_arm_embedded/bin/arm-none-eabi-gcc.exe 
Build flags: 
Id flags:  

The output was:
1
c:/gnu_arm_embedded/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld.exe: c:/gnu_arm_embedded/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib\libc.a(lib_a-exit.o): in function `exit':
exit.c:(.text.exit+0x2c): undefined reference to `_exit'
collect2.exe: error: ld returned 1 exit status


Compiling the CXX compiler identification source file "CMakeCXXCompilerId.cpp" failed.
Compiler: C:/gnu_arm_embedded/bin/arm-none-eabi-gcc.exe 
Build flags: 
Id flags:  

The output was:
1
c:/gnu_arm_embedded/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld.exe: c:/gnu_arm_embedded/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib\libc.a(lib_a-exit.o): in function `exit':
exit.c:(.text.exit+0x2c): undefined reference to `_exit'
collect2.exe: error: ld returned 1 exit status

CMakeOutput

The target system is: Generic - 2.4.0 - arm
The host system is: Windows - 10.0.19041 - AMD64
Compiling the C compiler identification source file "CMakeCCompilerId.c" succeeded.
Compiler: C:/gnu_arm_embedded/bin/arm-none-eabi-gcc.exe 
Build flags: 
Id flags: -c 

The output was:
0


Compilation of the C compiler identification source "CMakeCCompilerId.c" produced "CMakeCCompilerId.o"

The C compiler identification is GNU, found in "C:/Users/John/code/eip-zephyr/build/nrf52840dk_nrf52840/blinky/CMakeFiles/3.19.0/CompilerIdC/CMakeCCompilerId.o"

Compiling the CXX compiler identification source file "CMakeCXXCompilerId.cpp" succeeded.
Compiler: C:/gnu_arm_embedded/bin/arm-none-eabi-gcc.exe 
Build flags: 
Id flags: -c 

The output was:
0


Compilation of the CXX compiler identification source "CMakeCXXCompilerId.cpp" produced "CMakeCXXCompilerId.o"

The CXX compiler identification is GNU, found in "C:/Users/John/code/eip-zephyr/build/nrf52840dk_nrf52840/blinky/CMakeFiles/3.19.0/CompilerIdCXX/CMakeCXXCompilerId.o"

Checking whether the ASM compiler is GNU using "--version" matched "(GNU assembler)|(GCC)|(Free Software Foundation)":
arm-none-eabi-gcc.exe (GNU Arm Embedded Toolchain 9-2020-q2-update) 9.3.1 20200408 (release)
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

My Questions:

1. What does this error mean?
2. How do I fix it, so that I can build applications successfully.

Answer 1

After some digging and receiving help from others in the zephyr-rtos slack channel, I have found others experiencing the same problem, so I'll post my fix here in the hope that it solves other people's issues as well.

The fix is twofold:

1. You must downgrade from CMake 3.19. Most before this work, but 3.17.2 was the recommended version. If you're using windows, this can be done with the chocolatey command: choco install cmake --installargs 'ADD_CMAKE_TO_PATH=System' --version 3.17.2 --allow-downgrade --force.
2. You must remove the .cache folder. Your previous build output tells you where this will be stored. The line starts with like: "-- Cache files will be written too: ..."

I still don't know why this error gets thrown, or what should be done to fix it permanently, but this is a fix for now.

Answer 2

Just want to inform that a workaround is currently underway in the Zephyr repository. Have a look here: https://github.com/zephyrproject-rtos/zephyr/pull/30272