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())
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! >.<
This struct allows us to keep track of what memory is used by the loaded executable. For some reason, freeing this memory when the task exits triggers a kernel page fault, so I'm not doing that right now.
IT ACTUALLY WORKS NOW.
Why wasn't it working? Oh, because I was not setting already present page tables's permissions to user mode. Just a little bug. THAT I SPENT DAYS TRYING TO FIND
Anyways, it works now. Such a relief...
Yes, that's not completely-from-scratch.
But let's be honest, am I going to do everything from scratch? Probably not. I'm not making my own bootloader.
And making a proper smaller-than-4-KB allocator is not something I want to do.
Plus, liballoc works perfectly in this rewrite, seeing as the MM code actually works, instead of leaking all your poor memory
And liballoc_{lock, unlock} can be actually defined, since we have spinlocks here!
