Commit | Line | Data |
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3d083395 SR |
1 | /* |
2 | * Code for replacing ftrace calls with jumps. | |
3 | * | |
4 | * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com> | |
5 | * | |
6 | * Thanks goes to Ingo Molnar, for suggesting the idea. | |
7 | * Mathieu Desnoyers, for suggesting postponing the modifications. | |
8 | * Arjan van de Ven, for keeping me straight, and explaining to me | |
9 | * the dangers of modifying code on the run. | |
10 | */ | |
11 | ||
12 | #include <linux/spinlock.h> | |
13 | #include <linux/hardirq.h> | |
14 | #include <linux/ftrace.h> | |
15 | #include <linux/percpu.h> | |
16 | #include <linux/init.h> | |
17 | #include <linux/list.h> | |
18 | ||
dfa60aba | 19 | #include <asm/alternative.h> |
3d083395 | 20 | |
dfa60aba | 21 | #define CALL_BACK 5 |
3d083395 | 22 | |
dfa60aba SR |
23 | /* Long is fine, even if it is only 4 bytes ;-) */ |
24 | static long *ftrace_nop; | |
3d083395 | 25 | |
3d083395 SR |
26 | union ftrace_code_union { |
27 | char code[5]; | |
28 | struct { | |
29 | char e8; | |
30 | int offset; | |
31 | } __attribute__((packed)); | |
32 | }; | |
33 | ||
3c1720f0 SR |
34 | static int notrace ftrace_calc_offset(long ip, long addr) |
35 | { | |
36 | return (int)(addr - ip); | |
37 | } | |
3d083395 | 38 | |
3c1720f0 SR |
39 | notrace unsigned char *ftrace_nop_replace(void) |
40 | { | |
41 | return (char *)ftrace_nop; | |
42 | } | |
43 | ||
44 | notrace unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) | |
45 | { | |
46 | static union ftrace_code_union calc; | |
3d083395 | 47 | |
3c1720f0 SR |
48 | calc.e8 = 0xe8; |
49 | calc.offset = ftrace_calc_offset(ip, addr); | |
50 | ||
51 | /* | |
52 | * No locking needed, this must be called via kstop_machine | |
53 | * which in essence is like running on a uniprocessor machine. | |
54 | */ | |
55 | return calc.code; | |
3d083395 SR |
56 | } |
57 | ||
3c1720f0 | 58 | notrace int |
3d083395 SR |
59 | ftrace_modify_code(unsigned long ip, unsigned char *old_code, |
60 | unsigned char *new_code) | |
61 | { | |
dfa60aba SR |
62 | unsigned replaced; |
63 | unsigned old = *(unsigned *)old_code; /* 4 bytes */ | |
64 | unsigned new = *(unsigned *)new_code; /* 4 bytes */ | |
65 | unsigned char newch = new_code[4]; | |
3d083395 SR |
66 | int faulted = 0; |
67 | ||
3c1720f0 SR |
68 | /* move the IP back to the start of the call */ |
69 | ip -= CALL_BACK; | |
70 | ||
3d083395 SR |
71 | /* |
72 | * Note: Due to modules and __init, code can | |
73 | * disappear and change, we need to protect against faulting | |
74 | * as well as code changing. | |
75 | * | |
76 | * No real locking needed, this code is run through | |
77 | * kstop_machine. | |
78 | */ | |
79 | asm volatile ( | |
80 | "1: lock\n" | |
dfa60aba SR |
81 | " cmpxchg %3, (%2)\n" |
82 | " jnz 2f\n" | |
83 | " movb %b4, 4(%2)\n" | |
3d083395 SR |
84 | "2:\n" |
85 | ".section .fixup, \"ax\"\n" | |
a56be3fe SR |
86 | "3: movl $1, %0\n" |
87 | " jmp 2b\n" | |
3d083395 SR |
88 | ".previous\n" |
89 | _ASM_EXTABLE(1b, 3b) | |
90 | : "=r"(faulted), "=a"(replaced) | |
ee4311ad | 91 | : "r"(ip), "r"(new), "c"(newch), |
dfa60aba | 92 | "0"(faulted), "a"(old) |
3d083395 SR |
93 | : "memory"); |
94 | sync_core(); | |
95 | ||
dfa60aba | 96 | if (replaced != old && replaced != new) |
3d083395 SR |
97 | faulted = 2; |
98 | ||
99 | return faulted; | |
100 | } | |
101 | ||
d61f82d0 SR |
102 | notrace int ftrace_update_ftrace_func(ftrace_func_t func) |
103 | { | |
104 | unsigned long ip = (unsigned long)(&ftrace_call); | |
105 | unsigned char old[5], *new; | |
106 | int ret; | |
107 | ||
108 | ip += CALL_BACK; | |
109 | ||
110 | memcpy(old, &ftrace_call, 5); | |
111 | new = ftrace_call_replace(ip, (unsigned long)func); | |
112 | ret = ftrace_modify_code(ip, old, new); | |
113 | ||
114 | return ret; | |
115 | } | |
116 | ||
117 | notrace int ftrace_mcount_set(unsigned long *data) | |
118 | { | |
119 | unsigned long ip = (long)(&mcount_call); | |
120 | unsigned long *addr = data; | |
121 | unsigned char old[5], *new; | |
122 | ||
123 | /* ip is at the location, but modify code will subtact this */ | |
124 | ip += CALL_BACK; | |
125 | ||
126 | /* | |
127 | * Replace the mcount stub with a pointer to the | |
128 | * ip recorder function. | |
129 | */ | |
130 | memcpy(old, &mcount_call, 5); | |
131 | new = ftrace_call_replace(ip, *addr); | |
132 | *addr = ftrace_modify_code(ip, old, new); | |
133 | ||
134 | return 0; | |
135 | } | |
136 | ||
137 | int __init ftrace_dyn_arch_init(void *data) | |
3d083395 | 138 | { |
dfa60aba | 139 | const unsigned char *const *noptable = find_nop_table(); |
3d083395 | 140 | |
d61f82d0 SR |
141 | /* This is running in kstop_machine */ |
142 | ||
143 | ftrace_mcount_set(data); | |
144 | ||
dfa60aba SR |
145 | ftrace_nop = (unsigned long *)noptable[CALL_BACK]; |
146 | ||
3d083395 SR |
147 | return 0; |
148 | } | |
3c1720f0 | 149 |