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

//go:build linux && arm64

package debug

// Regs holds the full general-purpose register set of a traced process
// (the Linux arm64 user_pt_regs layout).
type Regs struct {
	X0     uint64
	X1     uint64
	X2     uint64
	X3     uint64
	X4     uint64
	X5     uint64
	X6     uint64
	X7     uint64
	X8     uint64
	X9     uint64
	X10    uint64
	X11    uint64
	X12    uint64
	X13    uint64
	X14    uint64
	X15    uint64
	X16    uint64
	X17    uint64
	X18    uint64
	X19    uint64
	X20    uint64
	X21    uint64
	X22    uint64
	X23    uint64
	X24    uint64
	X25    uint64
	X26    uint64
	X27    uint64
	X28    uint64
	X29    uint64 // FP (frame pointer)
	X30    uint64 // LR (link register)
	SP     uint64
	PC     uint64
	PSTATE uint64
}

// PC returns the program counter.
func (r *Regs) GetPC() uint64 { return r.PC }

// SetPC sets the program counter.
func (r *Regs) SetPC(pc uint64) { r.PC = pc }

// GetSP returns the stack pointer.
func (r *Regs) GetSP() uint64 { return r.SP }

// RegValue returns the value of the named register, or false if unknown.
func (r *Regs) RegValue(name string) (uint64, bool) {
	switch name {
	case "x0":
		return r.X0, true
	case "x1":
		return r.X1, true
	case "x2":
		return r.X2, true
	case "x3":
		return r.X3, true
	case "x4":
		return r.X4, true
	case "x5":
		return r.X5, true
	case "x6":
		return r.X6, true
	case "x7":
		return r.X7, true
	case "x8":
		return r.X8, true
	case "x9":
		return r.X9, true
	case "x10":
		return r.X10, true
	case "x11":
		return r.X11, true
	case "x12":
		return r.X12, true
	case "x13":
		return r.X13, true
	case "x14":
		return r.X14, true
	case "x15":
		return r.X15, true
	case "x16":
		return r.X16, true
	case "x17":
		return r.X17, true
	case "x18":
		return r.X18, true
	case "x19":
		return r.X19, true
	case "x20":
		return r.X20, true
	case "x21":
		return r.X21, true
	case "x22":
		return r.X22, true
	case "x23":
		return r.X23, true
	case "x24":
		return r.X24, true
	case "x25":
		return r.X25, true
	case "x26":
		return r.X26, true
	case "x27":
		return r.X27, true
	case "x28":
		return r.X28, true
	case "x29", "fp":
		return r.X29, true
	case "x30", "lr":
		return r.X30, true
	case "sp":
		return r.SP, true
	case "pc":
		return r.PC, true
	default:
		return 0, false
	}
}

// breakpointInsn is the software breakpoint instruction (BRK #0).
var breakpointInsn = []byte{0x00, 0x00, 0x20, 0xD4} // BRK #0

// breakpointPCAdjust is how far PC is past the breakpoint instruction after
// a trap: 0, because the arm64 kernel delivers the BRK SIGTRAP with the PC
// still on the BRK.  do_el0_brk64 calls send_user_sigtrap, which uses
// instruction_pointer(regs) unmodified (arch/arm64/kernel/debug-monitors.c);
// only the kernel-internal skip paths advance the PC.  GDB history agrees:
// decr_pc_after_break on aarch64 Linux is 0 (the +4 variant was a QEMU bug,
// sourceware PR 17280).
const breakpointPCAdjust = 0