The exit() libc function already accepted an integer, but didn't pass it on to the kernel since we had no mechanism for it to do that.
Now, the kernel stores a task's exit status to display it later (and in the future, return it to userspace via wait()/waitpid())
We don't have files :) (yet)
But if someone wants to fprintf(stderr), then fine. Do it. Except it won't be any different from fprintf(stdout) or printf().
Kernel: Add an errno.h header with definitions for each header,
and return those, negated, from syscalls when there is an error.
mmap() returns an invalid address with errno encoded, instead of
returning a negated errno; this address is encoded as ffffffffffffffEE
where EE is errno in hex.
libc: make syscall() return -1 and set errno on error, instead of
returning the raw return value of the system call. Also, add mmap()
and munmap() wrappers in sys/mman.h :).
userspace: make the memeater program show the value of errno
when allocating memory fails.
Things to improve: add perror() and strerror() to make the errno
experience even better! >.<
