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/*
* Copyright (C) 2008 Matt Fleming <mjf@gentoo.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 __init ftrace_dyn_arch_init(void *data)
{
/* The return code is retured via data */
__raw_writel(0, (unsigned long)data);
return 0;
}
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