path: root/arch/arm/kernel/kprobes-thumb.c

/*
 * arch/arm/kernel/kprobes-thumb.c
 *
 * Copyright (C) 2011 Jon Medhurst <tixy@yxit.co.uk>.
 *
 * 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.
 */

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

#include "kprobes.h"


/*
 * True if current instruction is in an IT block.
 */
#define in_it_block(cpsr)	((cpsr & 0x06000c00) != 0x00000000)

/*
 * Return the condition code to check for the currently executing instruction.
 * This is in ITSTATE<7:4> which is in CPSR<15:12> but is only valid if
 * in_it_block returns true.
 */
#define current_cond(cpsr)	((cpsr >> 12) & 0xf)

/*
 * Return the PC value for a probe in thumb code.
 * This is the address of the probed instruction plus 4.
 * We subtract one because the address will have bit zero set to indicate
 * a pointer to thumb code.
 */
static inline unsigned long __kprobes thumb_probe_pc(struct kprobe *p)
{
	return (unsigned long)p->addr - 1 + 4;
}

static void __kprobes
t32_simulate_table_branch(struct kprobe *p, struct pt_regs *regs)
{
	kprobe_opcode_t insn = p->opcode;
	unsigned long pc = thumb_probe_pc(p);
	int rn = (insn >> 16) & 0xf;
	int rm = insn & 0xf;

	unsigned long rnv = (rn == 15) ? pc : regs->uregs[rn];
	unsigned long rmv = regs->uregs[rm];
	unsigned int halfwords;

	if (insn & 0x10) /* TBH */
		halfwords = ((u16 *)rnv)[rmv];
	else /* TBB */
		halfwords = ((u8 *)rnv)[rmv];

	regs->ARM_pc = pc + 2 * halfwords;
}

static void __kprobes
t32_simulate_mrs(struct kprobe *p, struct pt_regs *regs)
{
	kprobe_opcode_t insn = p->opcode;
	int rd = (insn >> 8) & 0xf;
	unsigned long mask = 0xf8ff03df; /* Mask out execution state */
	regs->uregs[rd] = regs->ARM_cpsr & mask;
}

static void __kprobes
t32_simulate_cond_branch(struct kprobe *p, struct pt_regs *regs)
{
	kprobe_opcode_t insn = p->opcode;
	unsigned long pc = thumb_probe_pc(p);

	long offset = insn & 0x7ff;		/* imm11 */
	offset += (insn & 0x003f0000) >> 5;	/* imm6 */
	offset += (insn & 0x00002000) << 4;	/* J1 */
	offset += (insn & 0x00000800) << 7;	/* J2 */
	offset -= (insn & 0x04000000) >> 7;	/* Apply sign bit */

	regs->ARM_pc = pc + (offset * 2);
}

static enum kprobe_insn __kprobes
t32_decode_cond_branch(kprobe_opcode_t insn, struct arch_specific_insn *asi)
{
	int cc = (insn >> 22) & 0xf;
	asi->insn_check_cc = kprobe_condition_checks[cc];
	asi->insn_handler = t32_simulate_cond_branch;
	return INSN_GOOD_NO_SLOT;
}

static void __kprobes
t32_simulate_branch(struct kprobe *p, struct pt_regs *regs)
{
	kprobe_opcode_t insn = p->opcode