// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

#include "textflag.h"

// ABI0 JIT trampoline for arm64.
//
// enterJIT saves the Go SP and LR, switches to the prepared stack, and
// branches to the JIT function.  When the function RETs (BR LR), control
// lands in leaveJIT, which restores the Go stack and returns.
//
// The prepared stack layout:
//   [0]   leaveJIT address (loaded into LR before jumping to fn)
//   [8]   ABI0 argument area

// func enterJIT(fn uintptr, stack uintptr)
TEXT ·enterJIT(SB), NOSPLIT, $0-16
	MOVD fn+0(FP), R0 // target function address
	MOVD R30, savedLR(SB) // save link register
	MOVD R3, savedSP(SB) // save Go stack pointer
	MOVD stack+8(FP), R3 // load prepared stack pointer
	MOVD 0(R3), R30 // load leaveJIT address into LR
	MOVD R3, RSP // switch to the prepared stack: SP stays on
	// the leave slot, so the kernel reads its
	// first argument at SP+8 per the frame
	// convention (amd64 lays the stack out the
	// same way)
	JMP  (R0) // branch to JIT function

	// func leaveJIT()
TEXT ·leaveJIT(SB), NOSPLIT, $0-0
	MOVD savedSP(SB), R3 // restore Go stack pointer
	MOVD R3, RSP
	MOVD savedLR(SB), R30 // restore link register
	RET  // return to Go caller

// leaveRawAddr holds the raw .abi0 address of leaveJIT, read by call_arm64.go
// in preference to reflect.ValueOf(leaveJIT), which returns the address of the
// ABIInternal wrapper the linker interposes: the wrapper's prologue clobbers
// the saved-register window the JIT call depends on.
GLOBL ·leaveRawAddr(SB), NOPTR, $8
DATA ·leaveRawAddr(SB)/8, $·leaveJIT(SB)

// Package-level storage for saved registers.
GLOBL savedLR(SB), NOPTR, $8

GLOBL savedSP(SB), NOPTR, $8