; ke_syscall.asm - INT 0x40 kernel entry (MASM64)
;
; On entry the CPU has pushed (ring-3 -> ring-0 transition):
;   SS, RSP, RFLAGS, CS, RIP    (on the kernel stack via TSS.RSP0)
; RAX = syscall number
; RCX, RDX, R8, R9              = args 0-3  (MS x64)
; R10, R11                      = args 4-5  (our extension)

EXTERN KeSyscallDispatch:PROC

.CODE

KeSyscallEntry PROC
    sub     rsp, 8              ; 16-byte align the stack frame

    ; We need to allocate 32 bytes for shadow space, plus 24 bytes for 
    ; the 3 stack arguments (a3, a4, a5), plus 8 bytes of padding to keep 
    ; the stack 16-byte aligned. Total = 64.
    sub     rsp, 64

    ; Place the 5th, 6th, and 7th arguments onto the stack for KeSyscallDispatch
    mov     [rsp + 32], r9      ; a3
    mov     [rsp + 40], r10     ; a4
    mov     [rsp + 48], r11     ; a5

    ; Shift the first 4 registers down one slot
    mov     r9, r8              ; a2
    mov     r8, rdx             ; a1
    mov     rdx, rcx            ; a0
    mov     rcx, rax            ; nr (syscall number)

    ; Call the C dispatcher
    call    KeSyscallDispatch

    add     rsp, 72             ; Clean up (64 + 8)
    iretq
KeSyscallEntry ENDP

; ---------------------------------------------------------------------------
; Fault stubs - print a message and halt. A real kernel would do a bugcheck.
; ---------------------------------------------------------------------------
EXTERN KePanic:PROC

FaultMsg DB "KERNEL FAULT: vector %d at RIP %016llx", 0Ah, 0

KeFaultDE PROC
    sub  rsp, 28h
    lea  rcx, FaultMsg
    mov  rdx, 0
    pop  r8                     ; RIP from the fault frame
    call KePanic
KeFaultDE ENDP

KeFaultGP PROC
    sub  rsp, 28h
    lea  rcx, FaultMsg
    mov  rdx, 13
    pop  rax                    ; error code
    pop  r8                     ; RIP
    call KePanic
KeFaultGP ENDP

KeFaultPF PROC
    sub  rsp, 28h
    lea  rcx, FaultMsg
    mov  rdx, 14
    pop  rax                    ; error code
    pop  r8                     ; RIP
    call KePanic
KeFaultPF ENDP

EXTERN KeIrqDispatch:PROC

IrqStub MACRO num
PUBLIC KeIrqStub&num
KeIrqStub&num PROC
    push    rax
    mov     al, num
    jmp     KeIrqCommon
KeIrqStub&num ENDP
ENDM

IrqStub 0
IrqStub 1
IrqStub 2
IrqStub 3
IrqStub 4
IrqStub 5
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IrqStub 13
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IrqStub 16
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IrqStub 22
IrqStub 23

KeIrqCommon PROC
    ; al = irq number, rax saved on stack
    ; Build a minimal calling-convention-safe frame
    push    rcx
    push    rdx
    push    r8
    push    r9
    push    r10
    push    r11
    movzx   ecx, al         ; first arg = irq number (rcx, Win64 ABI)
    sub     rsp, 32         ; shadow space
    call    KeIrqDispatch
    add     rsp, 32
    pop     r11
    pop     r10
    pop     r9
    pop     r8
    pop     rdx
    pop     rcx
    pop     rax
    iretq
KeIrqCommon ENDP

END