This changes a bunch of things that allows building with the musl C lib,
provided that `libucontext-dev` and `pkg-config` are installed.
Note that installing libucontext makes absolutely zero sense on C libs
that do natively provide this deprecated System V API, such as glibc.
Hence, it no sane glibc setup is expected to ever have libucontext
installed.
A main pain point was that argv and argc are expected to be passed to
init_fini handlers, but that is actually a glibc extension. This just
parses `/proc/self/cmdline` by hand to populate argv and argc during
startup, unless running on glibc.
Adds a separate board for native64 instead of the `NATIVE_64BIT` workaround.
The files in `boards/native64` are more or less dummy files and just include
the `boards/native` logic (similar to `openlabs-kw41z-mini-256kib`).
The main logic for native is in `makefiles/arch/native.inc.mk`, `cpu/native`
and `boards/native`.
The remaining changes concern the build system, and change native board checks
to native CPU checks to cover both boards.
Initial version to test 64 bit compatibility.
Instead of a separate board, the inital version for Linux/x86_64 is enabled
by setting the environment variable `NATIVE_64BIT=y` and compiling as usual.
Not currently implemented:
* Architectures other than x86_64 or operating systems other than Linux
* No FreeBSD support
* No Aarch support
* Rust support for x86_64
Unaligned accesses on x86(_64) are allowed, but slow. However, some host systems
might not be that forgiving. Aligning the stack to sizeof(uintptr_t) should be
a pretty safe safety measure.
And with this done, all casts of the stack pointer that increase alignment
requirements are now intermediately casted to `uintptr_t` to silence
warnings from -Wcast-align - after all the stacks are now manually aligned.
