// 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
	ADD  $8, R3, R3            // advance past return address
	MOVD R3, RSP               // switch to prepared stack
	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

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