; .asm

INCLUDE ksamd64.inc

; Note: MASM sucks

; branch hints
nottaken    textequ <byte 2Eh>
taken       textequ <byte 3Eh>

_text SEGMENT PARA 'code'

EXTERN ScheduleTask:PROC
EXTERN current_task:ptr

__readfsqword PROC
    mov rax,gs:[rcx]
    ret
__readfsqword ENDP

__writefsqword PROC
    mov gs:[rcx],rdx
    ret
__writefsqword ENDP

SwitchToNextTask PROC
    ; Save context
    push rbx
    push rbp
    push rsi
    push rdi
    push r12
    push r13
    push r14
    push r15

    ; Pass old stack pointer as register argument
    mov rcx,rsp

    sub rsp,32+8
    call ScheduleTask

    ; Return value is new stack to resume
    mov rsp,rax

    ; Restore context
    pop r15
    pop r14
    pop r13
    pop r12
    pop rdi
    pop rsi
    pop rbp
    pop rbx
    pop rax
    jmp rax
SwitchToNextTask ENDP

PUBLIC SwitchToTask
SwitchToTask PROC
    push rbx
    push rbp
    push rsi
    push rdi
    push r12
    push r13
    push r14
    push r15

    ; Save stack pointer of outgoing task
    mov [rdx],rsp

    ; Switch to new stack
    mov rsp,rcx

    pop r15
    pop r14
    pop r13
    pop r12
    pop rdi
    pop rsi
    pop rbp
    pop rbx
    pop rax
    jmp rax
SwitchToTask ENDP

; Stub loads register arguments from initial saved registers
PUBLIC StartNewTask
StartNewTask PROC
    mov rcx,r12
    mov rdx,r13
    mov r8,r14
    mov r9,r15
    jmp rbp
StartNewTask ENDP

_text ENDS

END