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/*
* 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/spinlock.h>
#include <linux/hardirq.h>
#include <linux/ftrace.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/list.h>
#include <asm/alternative.h>
#define CALL_BACK 5
/* Long is fine, even if it is only 4 bytes ;-) */
static long *ftrace_nop;
struct ftrace_record {
struct dyn_ftrace rec;
int failed;
} __attribute__((packed));
struct ftrace_page {
struct ftrace_page *next;
int index;
struct ftrace_record records[];
} __attribute__((packed));
#define ENTRIES_PER_PAGE \
((PAGE_SIZE - sizeof(struct ftrace_page)) / sizeof(struct ftrace_record))
/* estimate from running different kernels */
#define NR_TO_INIT 10000
#define MCOUNT_ADDR ((long)(&mcount))
union ftrace_code_union {
char code[5];
struct {
char e8;
int offset;
} __attribute__((packed));
};
static struct ftrace_page *ftrace_pages_start;
static struct ftrace_page *ftrace_pages;
notrace struct dyn_ftrace *ftrace_alloc_shutdown_node(unsigned long ip)
{
struct ftrace_record *rec;
unsigned long save;
ip -= CALL_BACK;
save = *(long *)ip;
/* If this was already converted, skip it */
if (save == *ftrace_nop)
return NULL;
if (ftrace_pages->index == ENTRIES_PER_PAGE) {
if (!ftrace_pages->next)
return NULL;
ftrace_pages = ftrace_pages->next;
}
rec = &ftrace_pages->records[ftrace_pages->index++];
return &rec->rec;
}
static int notrace
ftrace_modify_code(unsigned long ip, unsigned char *old_code,
unsigned char *new_code)
{
unsigned replaced;
unsigned old = *(unsigned *)old_code; /* 4 bytes */
unsigned new = *(unsigned *)new_code; /* 4 bytes */
unsigned char newch = new_code[4];
int faulted = 0;
/*
* Note: Due to modules and __init, code can
* disappear and change, we need to protect against faulting
* as well as code changing.
*
* No real locking needed, this code is run through
* kstop_machine.
*/
asm volatile (
"1: lock\n"
" cmpxchg %3, (%2)\n"
" jnz 2f\n"
" movb %b4, 4(%2)\n"
"2:\n"
".section .fixup, \"ax\"\n"
" movl $1, %0\n"
"3: jmp 2b\n"
".previous\n"
_ASM_EXTABLE(1b, 3b)
: "=r"(faulted), "=a"(replaced)
: "r"(ip), "r"(new), "r"(newch),
"0"(faulted), "a"(old)
: "memory");
sync_core();
if (replaced != old && replaced != new)
faulted = 2;
return faulted;
}
static int notrace ftrace_calc_offset(long ip)
{
return (int)(MCOUNT_ADDR - ip);
}
notrace void ftrace_code_disable(struct dyn_ftrace *rec)
{
unsigned long ip;
union ftrace_code_union save;
struct ftrace_record *r =
container_of(rec, struct ftrace_record, rec);
ip = rec->ip;
save.e8 = 0xe8;
save.offset = ftrace_calc_offset(ip);
/* move the IP back to the start of the call */
ip -= CALL_BACK;
r->failed = ftrace_modify_code(ip, save.code, (char *)ftrace_nop);
}
static void notrace ftrace_replace_code(int saved)
{
unsigned char *new = NULL, *old = NULL;
struct ftrace_record *rec;
struct ftrace_page *pg;
unsigned long ip;
int i;
if (saved)
old = (char *)ftrace_nop;
else
new = (char *)ftrace_nop;
for (pg = ftrace_pages_start; pg; pg = pg->next) {
for (i = 0; i < pg->index; i++) {
union ftrace_code_union calc;
rec = &pg->records[i];
/* don't modify code that has already faulted */
if (rec->failed)
continue;
ip = rec->rec.ip;
calc.e8 = 0xe8;
calc.offset = ftrace_calc_offset(ip);
if (saved)
new = calc.code;
else
old = calc.code;
ip -= CALL_BACK;
rec->failed = ftrace_modify_code(ip, old, new);
}
}
}
notrace void ftrace_startup_code(void)
{
ftrace_replace_code(1);
}
notrace void ftrace_shutdown_code(void)
{
ftrace_replace_code(0);
}
notrace void ftrace_shutdown_replenish(void)
{
if (ftrace_pages->next)
return;
/* allocate another page */
ftrace_pages->next = (void *)get_zeroed_page(GFP_KERNEL);
}
notrace int __init ftrace_shutdown_arch_init(void)
{
const unsigned char *const *noptable = find_nop_table();
struct ftrace_page *pg;
int cnt;
int i;
ftrace_nop = (unsigned long *)noptable[CALL_BACK];
/* allocate a few pages */
ftrace_pages_start = (void *)get_zeroed_page(GFP_KERNEL);
if (!ftrace_pages_start)
return -1;
/*
* Allocate a few more pages.
*
* TODO: have some parser search vmlinux before
* final linking to find all calls to ftrace.
* Then we can:
* a) know how many pages to allocate.
* and/or
* b) set up the table then.
*
* The dynamic code is still necessary for
* modules.
*/
pg = ftrace_pages = ftrace_pages_start;
cnt = NR_TO_INIT / ENTRIES_PER_PAGE;
for (i = 0; i < cnt; i++) {
pg->next = (void *)get_zeroed_page(GFP_KERNEL);
/* If we fail, we'll try later anyway */
if (!pg->next)
break;
pg = pg->next;
}
return 0;
}
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