# SPDX-License-Identifier: MIT
# SPDX-FileCopyrightText: 2025 Niels Martignène <niels.martignene@protonmail.com>

#if defined(__APPLE__)
    #define SYMBOL(Symbol) _ ## Symbol
#else
    #define SYMBOL(Symbol) Symbol
#endif

# Forward
# ----------------------------

#if defined(__APPLE__)
# Fix "arm64 function not 4-byte aligned" linker warnings
.p2align 2
#endif

# These three are the same, but they differ (in the C side) by their return type.
# Unlike the three next functions, these ones don't forward XMM argument registers.
.global SYMBOL(ForwardCallGG)
.global SYMBOL(ForwardCallF)
.global SYMBOL(ForwardCallDDDD)

# The X variants are slightly slower, and are used when XMM arguments must be forwarded.
.global SYMBOL(ForwardCallXGG)
.global SYMBOL(ForwardCallXF)
.global SYMBOL(ForwardCallXDDDD)

# Copy function pointer to r9, in order to save it through argument forwarding.
# Also make a copy of the SP to CallData::old_sp because the callback system might need it.
# Save RSP in r29 (non-volatile), and use carefully assembled stack provided by caller.
.macro prologue
    .cfi_startproc
    hint #34
    stp x29, x30, [sp, -16]!
    .cfi_def_cfa sp, 16
    .cfi_offset 29, 16
    .cfi_offset 30, 8
    mov x29, sp
    .cfi_def_cfa x29, 16
    str x29, [x2, 0]
    mov x9, x0
    add sp, x1, #136
.endm

# Call native function.
# Once done, restore normal stack pointer and return.
# The return value is passed untouched through r0, r1, v0 and/or v1.
.macro epilogue
    blr x9
    mov sp, x29
    .cfi_def_cfa sp, 16
    ldp x29, x30, [sp], 16
    .cfi_def_cfa sp, 0
    .cfi_restore 30
    .cfi_restore 29
    ret
    .cfi_endproc
.endm

# Prepare general purpose argument registers from array passed by caller.
.macro forward_gpr
    ldr x8, [x1, 64]
    ldp x6, x7, [x1, 48]
    ldp x4, x5, [x1, 32]
    ldp x2, x3, [x1, 16]
    ldp x0, x1, [x1, 0]
.endm

# Prepare vector argument registers from array passed by caller.
.macro forward_vec
    ldp d6, d7, [x1, 120]
    ldp d4, d5, [x1, 104]
    ldp d2, d3, [x1, 88]
    ldp d0, d1, [x1, 72]
.endm

SYMBOL(ForwardCallGG):
    prologue
    forward_gpr
    epilogue

SYMBOL(ForwardCallF):
    prologue
    forward_gpr
    epilogue

SYMBOL(ForwardCallDDDD):
    prologue
    forward_gpr
    epilogue

SYMBOL(ForwardCallXGG):
    prologue
    forward_vec
    forward_gpr
    epilogue

SYMBOL(ForwardCallXF):
    prologue
    forward_vec
    forward_gpr
    epilogue

SYMBOL(ForwardCallXDDDD):
    prologue
    forward_vec
    forward_gpr
    epilogue

# Callbacks
# ----------------------------

.global SYMBOL(RelayCallback)
.global SYMBOL(SwitchAndRelay)
.global SYMBOL(RelayDirect)
.global SYMBOL(TrampolineEnd)

# First, make a copy of the argument registers.
# Then call the C function RelayCallback with the following arguments:
# static trampoline ID, a pointer to the saved GPR array, a pointer to the stack
# arguments of this call, and a pointer to a struct that will contain the result registers.
# After the call, simply load these registers from the output struct.
.macro trampoline id
    .cfi_startproc
    hint #34
    mov x9, \id
    b RelayTrampoline
    .cfi_endproc
.endm

RelayTrampoline:
    .cfi_startproc
    stp x29, x30, [sp, -16]!
    .cfi_def_cfa sp, 16
    .cfi_offset 29, 16
    .cfi_offset 30, 8
    sub sp, sp, #192
    .cfi_def_cfa sp, 208
    stp x0, x1, [sp, 0]
    stp x2, x3, [sp, 16]
    stp x4, x5, [sp, 32]
    stp x6, x7, [sp, 48]
    str x8, [sp, 64]
    stp d0, d1, [sp, 72]
    stp d2, d3, [sp, 88]
    stp d4, d5, [sp, 104]
    stp d6, d7, [sp, 120]
    mov x0, x9
    mov x1, sp
    bl SYMBOL(RelayCallback)
    ldp x0, x1, [sp, 136]
    ldp d0, d1, [sp, 152]
    ldp d2, d3, [sp, 168]
    add sp, sp, #192
    .cfi_def_cfa sp, 16
    ldp x29, x30, [sp], 16
    .cfi_def_cfa sp, 0
    .cfi_restore 30
    .cfi_restore 29
    ret
    .cfi_endproc

# When a callback is relayed, Koffi will call into Node.js and V8 to execute Javascript.
# The problem is that we're still running on the separate Koffi stack, and V8 will
# probably misdetect this as a "stack overflow". We have to restore the old
# stack pointer, call Node.js/V8 and go back to ours.
# The first three parameters (x0, x1, x2) are passed through untouched.
SYMBOL(SwitchAndRelay):
    .cfi_startproc
    hint #34
    stp x29, x30, [sp, -16]!
    .cfi_def_cfa sp, 16
    .cfi_offset 29, 16
    .cfi_offset 30, 8
    mov x29, sp
    ldr x9, [x4, 0]
    sub x9, sp, x9
    and x9, x9, #-16
    str x9, [x4, 8]
    mov sp, x3
    bl SYMBOL(RelayDirect)
    mov sp, x29
    .cfi_def_cfa sp, 16
    ldp x29, x30, [sp], 16
    .cfi_def_cfa sp, 0
    .cfi_restore 30
    .cfi_restore 29
    ret
    .cfi_endproc

#include "gnu.inc"

SYMBOL(TrampolineEnd):
    ret
