A standard libc would normally use the kernel's syscall interface to
connect with the lower level, and this interface would usually imitate
POSIX or a similar style. With the statically-linked unikernel design,
the syscalls would be functions, but the interface wouldn't change much.
However, there are some fundamental differences. For instance, in gint
there aren't separate kernel/userspace memory allocators, there's just a
unified allocator in the kernel. This makes malloc() conceptually a
direct syscall, which pushes the kernel/libc boundary at an unusual
location.
Having a clearly-marked HAL makes it easier to identify where the
boundary is. Code from <time.h> currently has an ad-hoc interface which
should be replaced with clock_gettime(2) in the future.
The HAL offers default implementations but these aren't used by gint
yet, because it's more practical to have undefined references than to
end up with the stubs in an executable. These are provided for future
completeness.
This change does not lift the requirement to recursively link gint with
the libc and the libc with gint.
Using the _Atomic types is technically more accurate, but equivalent in
practice (glibc uses a normal int) and a bit of a headache for C++
targets since _Atomic is replaced with std::atomic.
GCC's default stdint.h only defaults to stdint-gcc.h, which we want to
use, when using -ffreestanding. Make our wishes explicit to avoid
needing that flag.
@update
> CMakeLists.txt
| remove the generation of the shared version of the fxlibc (deprecated, unused)
> include/errno
| add some error macros needed in vhex
> src/string/strerror
| add EINTR support
| add EAGAIN support
| add ENOMEDIUM support
| add EMEDIUMTYPE support
@fix
> include/target/vhex
| add missing headers
This version of signal (which does not rely on a notion of userland
processes and is thus excluded from Vhex) follows C99 semantics but does
not generate any signals by default.
Basically, the signal function sets up function pointers and the signal
function calls them. Termination signals call exit() while other signals
call _Exit(), which is a quicker program termination similar to abort().
C99 allows programs to long jump out of signal handlers (!) which is
unbelievably scary because it would bypass stack switching code in Vhex
as well as normal interrupt handler termination in gint.
This is implemented for gint only currently; on Vhex, _Exit() is likely
just going to be a syscall. For CASIOWIN, this is slightly more
difficult, as there is no native exit syscall.
