global syscall_entry:function
global ksyscall:function

extern printk
extern allstop
extern need_schedule

; syscall to kernel
; syscall number in rax
; fourth argument (rcx) on stack?
ksyscall:
	; syscall over-writes rcx, save it
	push rcx
	syscall
	pop rcx
	ret

%define STAR 0xC0000081
%define LSTAR 0xC0000082
%define FMASK 0xC0000084

extern enable_syscall

global init_syscalls:function
init_syscalls:
	; STAR register
	mov ecx, STAR
	rdmsr
	mov edx, 0x23 ; user code segment / user data segment / 64 bit user code segment
	shr edx, 16
	or edx, 0x10 ; kernel code segment
	wrmsr

	; syscall rip
	mov rax, qword syscall_entry
	mov rdx, qword syscall_entry
	shr rdx, 32
	mov ecx, LSTAR
	wrmsr

	; rflags mask
	mov ecx, FMASK
	rdmsr
	mov eax, ~0x202
	wrmsr

	; turn on the enable bit (bit 1 of EFER, iirc)
	call enable_syscall
	ret
	
; still using user stack and memory map
; can't use user's stack because user may lie about where it is
; causing us to overwrite memory.

extern sleep
extern timer_ticks

syscall_entry:
	mov dr0, rcx
	mov dr1, rax
	mov dr2, rdi

	; TODO switch to kernel stack

	; save values for sysret
	push r11
	push rcx
	mov r10, rcx ; fourth arg in r10, since syscall clobbers rcx

	push rax
	push rdi
	push rsi
	mov r8, rdi
	mov r9, rsi

	mov rdi, qword sleepstr
	mov rdx, qword timer_ticks
	mov rsi, [rdx]
	mov edx, 0
	mov ecx, eax

	call printk
	pop rsi
	pop rdi
	pop rax

	call sleep

	; syscall number in rax
	; rcx would be the fourth argument, but over-written by syscall
	; so we pass it in r10, another scratch register

	; may not need to check for schedule, the syscall itself
	; should do a yield if it wants to

	; need to check for schedule, could possible just do
	; an interrupt if it needed scheduling
	call need_schedule
	mov dr1, rax
	;call allstop
	test eax,eax
	jz .nosched
	mov eax, 0x1123f982
	mov dr0, rax
	call allstop
	int 0x81 ; force a schedule call, any int would do actually
.nosched:

	mov eax, __LINE__
	mov dr3, rax
	mov dr2, r11
	mov dr1, rcx
	;call allstop

	pop rcx
	pop r11
	db 0x48 ; no sysretq in yasm
	sysret

ign:
db	'ignoring syscall %u', 0xa, 0

sleepstr:
	db '%u pid %u syscall %u : %u %u', 0xa, 0