ftrace.c

/*
 * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
 *
 * Code for replacing ftrace calls with jumps.
 *
 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
 *
 * Thanks goes to Ingo Molnar, for suggesting the idea.
 * Mathieu Desnoyers, for suggesting postponing the modifications.
 * Arjan van de Ven, for keeping me straight, and explaining to me
 * the dangers of modifying code on the run.
 */
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/io.h>
#include <asm/ftrace.h>
#include <asm/cacheflush.h>

static unsigned char ftrace_nop[] = {
	0x09, 0x00,		/* nop */
	0x09, 0x00,		/* nop */
};

static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];

unsigned char *ftrace_nop_replace(void)
{
	return ftrace_nop;
}

static int is_sh_nop(unsigned char *ip)
{
	return strncmp(ip, ftrace_nop, sizeof(ftrace_nop));
}

unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
{
	/* Place the address in the memory table. */
	if (addr == CALLER_ADDR)
		__raw_writel(addr + MCOUNT_INSN_OFFSET, ftrace_replaced_code);
	else
		__raw_writel(addr, ftrace_replaced_code);

	/*
	 * No locking needed, this must be called via kstop_machine
	 * which in essence is like running on a uniprocessor machine.
	 */
	return ftrace_replaced_code;
}

int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
		       unsigned char *new_code)
{
	unsigned char replaced[MCOUNT_INSN_SIZE];

	/*
	 * Note: Due to modules and __init, code can
	 *  disappear and change, we need to protect against faulting
	 *  as well as code changing. We do this by using the
	 *  probe_kernel_* functions.
	 *
	 * No real locking needed, this code is run through
	 * kstop_machine, or before SMP starts.
	 */

	/*
	 * If we're trying to nop out a call to a function, we instead
	 * place a call to the address after the memory table.
	 */
	if (is_sh_nop(new_code) == 0)
		__raw_writel(ip + MCOUNT_INSN_SIZE, (unsigned long)new_code);

	/* read the text we want to modify */
	if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
		return -EFAULT;

	/* Make sure it is what we expect it to be */
	if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
		return -EINVAL;

	/* replace the text with the new text */
	if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
		return -EPERM;

	flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);

	return 0;
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
	unsigned long ip = (unsigned long)(&ftrace_call);
	unsigned char old[MCOUNT_INSN_SIZE], *new;

	memcpy(old, (unsigned char *)(ip + MCOUNT_INSN_OFFSET), MCOUNT_INSN_SIZE);
	new = ftrace_call_replace(ip, (unsigned long)func);

	return ftrace_modify_code(ip + MCOUNT_INSN_OFFSET, old, new);
}

int ftrace_make_nop(struct module *mod,
		    struct dyn_ftrace *rec, unsigned long addr)
{
	unsigned char *new, *old;
	unsigned long ip = rec->ip;

	old = ftrace_call_replace(ip, addr);
	new = ftrace_nop_replace();

	return ftrace_modify_code(rec->ip, old, new);
}

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
	unsigned char *new, *old;
	unsigned long ip = rec->ip;

	old = ftrace_nop_replace();
	new = ftrace_call_replace(ip, addr);

	return ftrace_modify_code(rec->ip, old, new);
}

int __init ftrace_dyn_arch_init(void *data)
{
	/* The return code is retured via data */
	__raw_writel(0, (unsigned long)data);

	return 0;
}