1 /*
2 * Copyright (C) 2008 Matt Fleming <mjf@gentoo.org>
3 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
4 *
5 * Code for replacing ftrace calls with jumps.
6 *
7 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
8 *
9 * Thanks goes to Ingo Molnar, for suggesting the idea.
10 * Mathieu Desnoyers, for suggesting postponing the modifications.
11 * Arjan van de Ven, for keeping me straight, and explaining to me
12 * the dangers of modifying code on the run.
13 */
14 #include <linux/uaccess.h>
15 #include <linux/ftrace.h>
16 #include <linux/string.h>
17 #include <linux/init.h>
18 #include <linux/io.h>
19 #include <asm/ftrace.h>
20 #include <asm/cacheflush.h>
21
22 static unsigned char ftrace_nop[] = {
23 0x09, 0x00, /* nop */
24 0x09, 0x00, /* nop */
25 };
26
27 static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
28
ftrace_nop_replace(void)29 unsigned char *ftrace_nop_replace(void)
30 {
31 return ftrace_nop;
32 }
33
is_sh_nop(unsigned char * ip)34 static int is_sh_nop(unsigned char *ip)
35 {
36 return strncmp(ip, ftrace_nop, sizeof(ftrace_nop));
37 }
38
ftrace_call_replace(unsigned long ip,unsigned long addr)39 unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
40 {
41 /* Place the address in the memory table. */
42 if (addr == CALLER_ADDR)
43 __raw_writel(addr + MCOUNT_INSN_OFFSET, ftrace_replaced_code);
44 else
45 __raw_writel(addr, ftrace_replaced_code);
46
47 /*
48 * No locking needed, this must be called via kstop_machine
49 * which in essence is like running on a uniprocessor machine.
50 */
51 return ftrace_replaced_code;
52 }
53
ftrace_modify_code(unsigned long ip,unsigned char * old_code,unsigned char * new_code)54 int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
55 unsigned char *new_code)
56 {
57 unsigned char replaced[MCOUNT_INSN_SIZE];
58
59 /*
60 * Note: Due to modules and __init, code can
61 * disappear and change, we need to protect against faulting
62 * as well as code changing. We do this by using the
63 * probe_kernel_* functions.
64 *
65 * No real locking needed, this code is run through
66 * kstop_machine, or before SMP starts.
67 */
68
69 /*
70 * If we're trying to nop out a call to a function, we instead
71 * place a call to the address after the memory table.
72 */
73 if (is_sh_nop(new_code) == 0)
74 __raw_writel(ip + MCOUNT_INSN_SIZE, (unsigned long)new_code);
75
76 /* read the text we want to modify */
77 if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
78 return -EFAULT;
79
80 /* Make sure it is what we expect it to be */
81 if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
82 return -EINVAL;
83
84 /* replace the text with the new text */
85 if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
86 return -EPERM;
87
88 flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
89
90 return 0;
91 }
92
ftrace_update_ftrace_func(ftrace_func_t func)93 int ftrace_update_ftrace_func(ftrace_func_t func)
94 {
95 unsigned long ip = (unsigned long)(&ftrace_call);
96 unsigned char old[MCOUNT_INSN_SIZE], *new;
97
98 memcpy(old, (unsigned char *)(ip + MCOUNT_INSN_OFFSET), MCOUNT_INSN_SIZE);
99 new = ftrace_call_replace(ip, (unsigned long)func);
100
101 return ftrace_modify_code(ip + MCOUNT_INSN_OFFSET, old, new);
102 }
103
ftrace_make_nop(struct module * mod,struct dyn_ftrace * rec,unsigned long addr)104 int ftrace_make_nop(struct module *mod,
105 struct dyn_ftrace *rec, unsigned long addr)
106 {
107 unsigned char *new, *old;
108 unsigned long ip = rec->ip;
109
110 old = ftrace_call_replace(ip, addr);
111 new = ftrace_nop_replace();
112
113 return ftrace_modify_code(rec->ip, old, new);
114 }
115
ftrace_make_call(struct dyn_ftrace * rec,unsigned long addr)116 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
117 {
118 unsigned char *new, *old;
119 unsigned long ip = rec->ip;
120
121 old = ftrace_nop_replace();
122 new = ftrace_call_replace(ip, addr);
123
124 return ftrace_modify_code(rec->ip, old, new);
125 }
126
ftrace_dyn_arch_init(void * data)127 int __init ftrace_dyn_arch_init(void *data)
128 {
129 /* The return code is retured via data */
130 __raw_writel(0, (unsigned long)data);
131
132 return 0;
133 }
134