There are a lot of under the hood changes here:
- Move syscalls to be a dispatch table, defined by syscalls.inc
- Don't need a full process state (push_all) in syscalls now
- In push_all, define REGS instead of using offsets
- Save TWO stack pointers as well as current saved stack pointer in TCB:
- rsp0 is the base of the kernel stack for interrupts
- rsp3 is the saved user stack from cpu_data
- Update syscall numbers in nulldrv
- Some asm-debugging enhancements to the gdb script
- fork() still not working
Previously CPU statue was passed on the stack, but the compiler is
allowed to clobber values passed to it on the stack in the SysV x86 ABI.
So now leave the state on the stack but pass a pointer to it into the
ISR functions.
Processes can now wait on signals/children/time. There is no clock
currently so "time" is just a monotonically increating tick count. Added
a SLEEP syscall to test this waiting/waking.
The syscall/sysret instructions don't swap stacks. This was bad but
passable until syscalls caused the scheduler to run, and scheduling a
task that paused due to interrupt.
Adding a new (hopefully temporary) syscall interrupt `int 0xee` to allow
me to test syscalls without stack issues before I tackle the
syscall/sysret issue.
Also implemented a basic `pause` syscall that causes the calling process
to become unready. Because nothing can wake a process yet, it never
returns.
