/*
* 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 <linux/kernel.h>
#include <asm/ftrace.h>
#include <asm/cacheflush.h>
#include <asm/unistd.h>
#include <trace/syscall.h>
#ifdef CONFIG_DYNAMIC_FTRACE
static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
static unsigned char ftrace_nop[4];
/*
* If we're trying to nop out a call to a function, we instead
* place a call to the address after the memory table.
*
* 8c011060 <a>:
* 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1
* 8c011062: 22 4f sts.l pr,@-r15
* 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0
* 8c011066: 2b 41 jmp @r1
* 8c011068: 2a 40 lds r0,pr
* 8c01106a: 09 00 nop
* 8c01106c: 68 24 .word 0x2468 <--- ip
* 8c01106e: 1d 8c .word 0x8c1d
* 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE
*
* We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
* past the _mcount call and continue executing code like normal.
*/
static unsigned char *ftrace_nop_replace(unsigned long ip)
{
__raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
return ftrace_nop;
}
static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
{
/* Place the address in the memory table. */
__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;
}
/*
* Modifying code must take extra care. On an SMP machine, if
* the code being modified is also being executed on another CPU
* that CPU will have undefined results and possibly take a GPF.
* We use kstop_machine to stop other CPUS from exectuing code.
* But this does not stop NMIs from happening. We still need
* to protect against that. We separate out the modification of
* the code to take care of this.
*
* Two buffers are added: An IP buffer and a "code" buffer.
*
* 1) Put the instruction pointer into the IP buffer
* and the new code into the "code" buffer.
* 2) Wait for any running NMIs to finish and set a flag that says
* we are modifying code, it is done in an atomic operation.
* 3) Write the code
* 4) clear the flag.
* 5) Wait for any running NMIs to finish.
*
* If an NMI is executed, the first thing it does is to call
* "ftrace_nmi_enter". This will check if the flag is set to write
* and if it is, it will write what is in the IP and "code" buffers.
*
* The trick is, it does not matter if everyone is writing the same
* content to the code location. Also, if a CPU is executing code
* it is OK to write to that code location if the contents being written
* are the same as what exists.
*/
#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
static atomic_t nmi_running = ATOMIC_INIT(0);
static int mod_code_status; /* holds return value of text write */
static void *mod_code_ip; /* holds the IP to write to */
static void *mod_code_newcode; /* holds the text to write to the IP */
static unsigned nmi_wait_count;
static atomic_t nmi_update_count = ATOMIC_INIT(0);
int ftrace_arch_read_dyn_info(char *buf, int size)
{
int r;
r = snprintf(buf, size, "%u %u",
nmi_wait_count,
atomic_read(&nmi_update_count));
return r;
}
static void clear_mod_flag(void)
{
int old = atomic_read(&nmi_running);
for (;;) {
int new = old & ~MOD_CODE_WRITE_FLAG;
if (old == new)
break;
old = atomic_cmpxchg(&nmi_running, old, new);
}
}
static void ftrace_mod_code(void)
{
/*
* Yes, more than one CPU process can be writing to mod_code_status.
* (and the code itself)
* But if one were to fail, then they all should, and if one were
* to succeed, then they all should.
*/
mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
MCOUNT_INSN_SIZE);
/* if we fail, then kill any new writers */
if (mod_code_status)
clear_mod_flag();
}
void ftrace_nmi_enter(void)
{
if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
smp_rmb();
ftrace_mod_code();
atomic_inc(&nmi_update_count);
}
/* Must have previous changes seen before executions */
smp_mb();
}
void ftrace_nmi_exit(void)
{
/* Finish all executions before clearing nmi_running */
smp_mb();
atomic_dec(&nmi_running);
}
static void wait_for_nmi_and_set_mod_flag(void)
{
if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
return;
do {
cpu_relax();
} while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
nmi_wait_count++;
}
static void wait_for_nmi(void)
{
if (!atomic_read(&nmi_running))
return;
do {
cpu_relax();
} while (atomic_read(&nmi_running));
nmi_wait_count++;
}
static int
do_ftrace_mod_code(unsigned long ip, void *new_code)
{
mod_code_ip = (void *)ip;
mod_code_newcode = new_code;
/* The buffers need to be visible before we let NMIs write them */
smp_mb();
wait_for_nmi_and_set_mod_flag();
/* Make sure all running NMIs have finished before we write the code */
smp_mb();
ftrace_mod_code();
/* Make sure the write happens before clearing the bit */
smp_mb();
clear_mod_flag();
wait_for_nmi();
return mod_code_status;
}
static 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.
*/
/* 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 (do_ftrace_mod_code(ip, new_code))
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) + MCOUNT_INSN_OFFSET;
unsigned char old[MCOUNT_INSN_SIZE], *new;
memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
new = ftrace_call_replace(ip, (unsigned long)func);
return ftrace_modify_code(ip, 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(ip);
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(ip);
new = ftrace_call_replace(ip, addr);
return ftrace_modify_code(rec->ip, old, new);
}
int __init ftrace_dyn_arch_init(void)
{
return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
#ifdef CONFIG_DYNAMIC_FTRACE
extern void ftrace_graph_call(void);
static int ftrace_mod(unsigned long ip, unsigned long old_addr,
unsigned long new_addr)
{
unsigned char code[MCOUNT_INSN_SIZE];
if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
return -EFAULT;
if (old_addr != __raw_readl((unsigned long *)code))
return -EINVAL;
__raw_writel(new_addr, ip);
return 0;
}
int ftrace_enable_ftrace_graph_caller(void)
{
unsigned long ip, old_addr, new_addr;
ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
old_addr = (unsigned long)(&skip_trace);
new_addr = (unsigned long)(&ftrace_graph_caller);
return ftrace_mod(ip, old_addr, new_addr);
}
int ftrace_disable_ftrace_graph_caller(void)
{
unsigned long ip, old_addr, new_addr;
ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
old_addr = (unsigned long)(&ftrace_graph_caller);
new_addr = (unsigned long)(&skip_trace);
return ftrace_mod(ip, old_addr, new_addr);
}
#endif /* CONFIG_DYNAMIC_FTRACE */
/*
* Hook the return address and push it in the stack of return addrs
* in the current thread info.
*
* This is the main routine for the function graph tracer. The function
* graph tracer essentially works like this:
*
* parent is the stack address containing self_addr's return address.
* We pull the real return address out of parent and store it in
* current's ret_stack. Then, we replace the return address on the stack
* with the address of return_to_handler. self_addr is the function that
* called mcount.
*
* When self_addr returns, it will jump to return_to_handler which calls
* ftrace_return_to_handler. ftrace_return_to_handler will pull the real
* return address off of current's ret_stack and jump to it.
*/
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
{
unsigned long old;
int faulted, err;
struct ftrace_graph_ent trace;
unsigned long return_hooker = (unsigned long)&return_to_handler;
if (unlikely(ftrace_graph_is_dead()))
return;
if (unlikely(atomic_read(¤t->tracing_graph_pause)))
return;
/*
* Protect against fault, even if it shouldn't
* happen. This tool is too much intrusive to
* ignore such a protection.
*/
__asm__ __volatile__(
"1: \n\t"
"mov.l @%2, %0 \n\t"
"2: \n\t"
"mov.l %3, @%2 \n\t"
"mov #0, %1 \n\t"
"3: \n\t"
".section .fixup, \"ax\" \n\t"
"4: \n\t"
"mov.l 5f, %0 \n\t"
"jmp @%0 \n\t"
" mov #1, %1 \n\t"
".balign 4 \n\t"
"5: .long 3b \n\t"
".previous \n\t"
".section __ex_table,\"a\" \n\t"
".long 1b, 4b \n\t"
".long 2b, 4b \n\t"
".previous \n\t"
: "=&r" (old), "=r" (faulted)
: "r" (parent), "r" (return_hooker)
);
if (unlikely(faulted)) {
ftrace_graph_stop();
WARN_ON(1);
return;
}
err = ftrace_push_return_trace(old, self_addr, &trace.depth, 0);
if (err == -EBUSY) {
__raw_writel(old, parent);
return;
}
trace.func = self_addr;
/* Only trace if the calling function expects to */
if (!ftrace_graph_entry(&trace)) {
current->curr_ret_stack--;
__raw_writel(old, parent);
}
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */