This repository contains a minimum working example of a CMake config to build C source into a working firmware image for an ARM Cortex-M0 microcontroller.
The output ELF has been tested on an STM32L082CZ microcontroller via a debugger and appears to load and run.
This should build out-of-the-box with the version of clang that Apple provides in
the XCode command-line tools.
(which I think is pretty interesting, to use the exact same compiler that, say, CLion
uses by default)
Standard CMake build:
mkdir build
cd build
cmake ../
make
This build is linked against libc_nano and libnosys. As far as I have, found, there is not an
equivalent in clang for the --specs=nosys.specs inputs.
Additionally, I am not entirely sure of the implications of building and running with
libnosys, other than avoiding the provision of empty system-lib function stubs,
and libc_nano, other than using a smaller, lower-featured implementation of newlib.
I tested the use of float types in the trivial func implementation, and I observed
spurious values via a debugger; TODO.
The explicit linking with crt0, crti, crtn, crtbegin, and crtend objects from arm-gcc suggests that I do not have something configured correctly. Similarly, the convoluted path to pick up the right libraries indicates wrong or missing flags, options, etc.
During testing, I found that without a lot of caution around the paths and the various
versions of libcc.a and the crt*.o files, I would end up with Thumb code linked
into my ELF, resulting in a hardfault.