/*
 * arch/arm64/kernel/probes/simulate-insn.c
 *
 * Copyright (C) 2013 Linaro Limited.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */

#include <linux/bitops.h>
#include <linux/kernel.h>
#include <linux/kprobes.h>

#include <asm/ptrace.h>

#include "simulate-insn.h"

#define bbl_displacement(insn)          \
        sign_extend32(((insn) & 0x3ffffff) << 2, 27)

#define bcond_displacement(insn)        \
        sign_extend32(((insn >> 5) & 0x7ffff) << 2, 20)

#define cbz_displacement(insn)  \
        sign_extend32(((insn >> 5) & 0x7ffff) << 2, 20)

#define tbz_displacement(insn)  \
        sign_extend32(((insn >> 5) & 0x3fff) << 2, 15)

#define ldr_displacement(insn)  \
        sign_extend32(((insn >> 5) & 0x7ffff) << 2, 20)

static inline void set_x_reg(struct pt_regs *regs, int reg, u64 val)
{
        pt_regs_write_reg(regs, reg, val);
}

static inline void set_w_reg(struct pt_regs *regs, int reg, u64 val)
{
        pt_regs_write_reg(regs, reg, lower_32_bits(val));
}

static inline u64 get_x_reg(struct pt_regs *regs, int reg)
{
        return pt_regs_read_reg(regs, reg);
}

static inline u32 get_w_reg(struct pt_regs *regs, int reg)
{
        return lower_32_bits(pt_regs_read_reg(regs, reg));
}

static bool __kprobes check_cbz(u32 opcode, struct pt_regs *regs)
{
        int xn = opcode & 0x1f;

        return (opcode & (1 << 31)) ?
            (get_x_reg(regs, xn) == 0) : (get_w_reg(regs, xn) == 0);
}

static bool __kprobes check_cbnz(u32 opcode, struct pt_regs *regs)
{
        int xn = opcode & 0x1f;

        return (opcode & (1 << 31)) ?
            (get_x_reg(regs, xn) != 0) : (get_w_reg(regs, xn) != 0);
}

static bool __kprobes check_tbz(u32 opcode, struct pt_regs *regs)
{
        int xn = opcode & 0x1f;
        int bit_pos = ((opcode & (1 << 31)) >> 26) | ((opcode >> 19) & 0x1f);

        return ((get_x_reg(regs, xn) >> bit_pos) & 0x1) == 0;
}

static bool __kprobes check_tbnz(u32 opcode, struct pt_regs *regs)
{
        int xn = opcode & 0x1f;
        int bit_pos = ((opcode & (1 << 31)) >> 26) | ((opcode >> 19) & 0x1f);

        return ((get_x_reg(regs, xn) >> bit_pos) & 0x1) != 0;
}

/*
 * instruction simulation functions
 */
void __kprobes
simulate_adr_adrp(u32 opcode, long addr, struct pt_regs *regs)
{
        long imm, xn, val;

        xn = opcode & 0x1f;
        imm = ((opcode >> 3) & 0x1ffffc) | ((opcode >> 29) & 0x3);
        imm = sign_extend64(imm, 20);
        if (opcode & 0x80000000)
                val = (imm<<12) + (addr & 0xfffffffffffff000);
        else
                val = imm + addr;

        set_x_reg(regs, xn, val);

        instruction_pointer_set(regs, instruction_pointer(regs) + 4);
}

void __kprobes
simulate_b_bl(u32 opcode, long addr, struct pt_regs *regs)
{
        int disp = bbl_displacement(opcode);

        /* Link register is x30 */
        if (opcode & (1 << 31))
                set_x_reg(regs, 30, addr + 4);

        instruction_pointer_set(regs, addr + disp);
}

void __kprobes
simulate_b_cond(u32 opcode, long addr, struct pt_regs *regs)
{
        int disp = 4;

        if (aarch32_opcode_cond_checks[opcode & 0xf](regs->pstate & 0xffffffff))
                disp = bcond_displacement(opcode);

        instruction_pointer_set(regs, addr + disp);
}

void __kprobes
simulate_br_blr_ret(u32 opcode, long addr, struct pt_regs *regs)
{
        int xn = (opcode >> 5) & 0x1f;

        /* update pc first in case we're doing a "blr lr" */
        instruction_pointer_set(regs, get_x_reg(regs, xn));

        /* Link register is x30 */
        if (((opcode >> 21) & 0x3) == 1)
                set_x_reg(regs, 30, addr + 4);
}

void __kprobes
simulate_cbz_cbnz(u32 opcode, long addr, struct pt_regs *regs)
{
        int disp = 4;

        if (opcode & (1 << 24)) {
                if (check_cbnz(opcode, regs))
                        disp = cbz_displacement(opcode);
        } else {
                if (check_cbz(opcode, regs))
                        disp = cbz_displacement(opcode);
        }
        instruction_pointer_set(regs, addr + disp);
}

void __kprobes
simulate_tbz_tbnz(u32 opcode, long addr, struct pt_regs *regs)
{
        int disp = 4;

        if (opcode & (1 << 24)) {
                if (check_tbnz(opcode, regs))
                        disp = tbz_displacement(opcode);
        } else {
                if (check_tbz(opcode, regs))
                        disp = tbz_displacement(opcode);
        }
        instruction_pointer_set(regs, addr + disp);
}

void __kprobes
simulate_ldr_literal(u32 opcode, long addr, struct pt_regs *regs)
{
        u64 *load_addr;
        int xn = opcode & 0x1f;
        int disp;

        disp = ldr_displacement(opcode);
        load_addr = (u64 *) (addr + disp);

        if (opcode & (1 << 30)) /* x0-x30 */
                set_x_reg(regs, xn, *load_addr);
        else                    /* w0-w30 */
                set_w_reg(regs, xn, *load_addr);

        instruction_pointer_set(regs, instruction_pointer(regs) + 4);
}

void __kprobes
simulate_ldrsw_literal(u32 opcode, long addr, struct pt_regs *regs)
{
        s32 *load_addr;
        int xn = opcode & 0x1f;
        int disp;

        disp = ldr_displacement(opcode);
        load_addr = (s32 *) (addr + disp);

        set_x_reg(regs, xn, *load_addr);

        instruction_pointer_set(regs, instruction_pointer(regs) + 4);
}