I spent some time stuck on a problem where processes would clobber each
other's stacks. Took me a moment to figure out that their stacks
were allocated in the sub-4MB linear address range which is shared
between all processes. Oops!
This isn't finished but I'll commit as I go. We need to get to where context
switching only needs to change CR3 and everything's ready to go.
My basic idea is:
- The first 4 kB is off-limits. This catches null dereferences.
- Up to the 4 MB mark is identity-mapped and kernel-only.
- The rest is available to everyone!
While the first 4 MB is only available to the kernel, it's still mapped in
every process, for convenience when entering the kernel.
Sweet, now we can look at all the zones (physical memory) currently in play.
Building the procfs files with ksprintf and rickety buffer presizing feels
pretty shoddy but I'll fix it up eventually.
This shows some info about the MM. Right now it's just the zone count
and the number of free physical pages. Lots more can be added.
Also added "exit" to sh so we can nest shells and exit from them.
I also noticed that we were leaking all the physical pages, so fixed that.
This took me a couple hours. :^)
The ELF loading code now allocates a single region for the entire
file and creates virtual memory mappings for the sections as needed.
Very nice!
- Turn Keyboard into a CharacterDevice (85,1) at /dev/keyboard.
- Implement MM::unmapRegionsForTask() and MM::unmapRegion()
- Save SS correctly on interrupt.
- Add a simple Spawn syscall for launching another process.
- Move a bunch of IO syscall debug output behind DEBUG_IO.
- Have ASSERT do a "cli" immediately when failing.
This makes the output look proper every time.
- Implement a bunch of syscalls in LibC.
- Add a simple shell ("sh"). All it can do now is read a line
of text from /dev/keyboard and then try launching the specified
executable by calling spawn().
There are definitely bugs in here, but we're moving on forward.
