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> |
395a59d0 | 20 | #include <asm/ftrace.h> |
3d083395 | 21 | |
3d083395 | 22 | |
dfa60aba SR |
23 | /* Long is fine, even if it is only 4 bytes ;-) */ |
24 | static long *ftrace_nop; | |
3d083395 | 25 | |
3d083395 | 26 | union ftrace_code_union { |
395a59d0 | 27 | char code[MCOUNT_INSN_SIZE]; |
3d083395 SR |
28 | struct { |
29 | char e8; | |
30 | int offset; | |
31 | } __attribute__((packed)); | |
32 | }; | |
33 | ||
395a59d0 | 34 | |
3c1720f0 SR |
35 | static int notrace ftrace_calc_offset(long ip, long addr) |
36 | { | |
37 | return (int)(addr - ip); | |
38 | } | |
3d083395 | 39 | |
3c1720f0 SR |
40 | notrace unsigned char *ftrace_nop_replace(void) |
41 | { | |
42 | return (char *)ftrace_nop; | |
43 | } | |
44 | ||
45 | notrace unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) | |
46 | { | |
47 | static union ftrace_code_union calc; | |
3d083395 | 48 | |
3c1720f0 | 49 | calc.e8 = 0xe8; |
395a59d0 | 50 | calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr); |
3c1720f0 SR |
51 | |
52 | /* | |
53 | * No locking needed, this must be called via kstop_machine | |
54 | * which in essence is like running on a uniprocessor machine. | |
55 | */ | |
56 | return calc.code; | |
3d083395 SR |
57 | } |
58 | ||
3c1720f0 | 59 | notrace int |
3d083395 SR |
60 | ftrace_modify_code(unsigned long ip, unsigned char *old_code, |
61 | unsigned char *new_code) | |
62 | { | |
dfa60aba SR |
63 | unsigned replaced; |
64 | unsigned old = *(unsigned *)old_code; /* 4 bytes */ | |
65 | unsigned new = *(unsigned *)new_code; /* 4 bytes */ | |
66 | unsigned char newch = new_code[4]; | |
3d083395 SR |
67 | int faulted = 0; |
68 | ||
69 | /* | |
70 | * Note: Due to modules and __init, code can | |
71 | * disappear and change, we need to protect against faulting | |
72 | * as well as code changing. | |
73 | * | |
74 | * No real locking needed, this code is run through | |
75 | * kstop_machine. | |
76 | */ | |
77 | asm volatile ( | |
78 | "1: lock\n" | |
dfa60aba SR |
79 | " cmpxchg %3, (%2)\n" |
80 | " jnz 2f\n" | |
81 | " movb %b4, 4(%2)\n" | |
3d083395 SR |
82 | "2:\n" |
83 | ".section .fixup, \"ax\"\n" | |
a56be3fe SR |
84 | "3: movl $1, %0\n" |
85 | " jmp 2b\n" | |
3d083395 SR |
86 | ".previous\n" |
87 | _ASM_EXTABLE(1b, 3b) | |
88 | : "=r"(faulted), "=a"(replaced) | |
ee4311ad | 89 | : "r"(ip), "r"(new), "c"(newch), |
dfa60aba | 90 | "0"(faulted), "a"(old) |
3d083395 SR |
91 | : "memory"); |
92 | sync_core(); | |
93 | ||
dfa60aba | 94 | if (replaced != old && replaced != new) |
3d083395 SR |
95 | faulted = 2; |
96 | ||
97 | return faulted; | |
98 | } | |
99 | ||
d61f82d0 SR |
100 | notrace int ftrace_update_ftrace_func(ftrace_func_t func) |
101 | { | |
102 | unsigned long ip = (unsigned long)(&ftrace_call); | |
395a59d0 | 103 | unsigned char old[MCOUNT_INSN_SIZE], *new; |
d61f82d0 SR |
104 | int ret; |
105 | ||
395a59d0 | 106 | memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE); |
d61f82d0 SR |
107 | new = ftrace_call_replace(ip, (unsigned long)func); |
108 | ret = ftrace_modify_code(ip, old, new); | |
109 | ||
110 | return ret; | |
111 | } | |
112 | ||
113 | notrace int ftrace_mcount_set(unsigned long *data) | |
114 | { | |
115 | unsigned long ip = (long)(&mcount_call); | |
116 | unsigned long *addr = data; | |
395a59d0 | 117 | unsigned char old[MCOUNT_INSN_SIZE], *new; |
d61f82d0 SR |
118 | |
119 | /* | |
120 | * Replace the mcount stub with a pointer to the | |
121 | * ip recorder function. | |
122 | */ | |
395a59d0 | 123 | memcpy(old, &mcount_call, MCOUNT_INSN_SIZE); |
d61f82d0 SR |
124 | new = ftrace_call_replace(ip, *addr); |
125 | *addr = ftrace_modify_code(ip, old, new); | |
126 | ||
127 | return 0; | |
128 | } | |
129 | ||
130 | int __init ftrace_dyn_arch_init(void *data) | |
3d083395 | 131 | { |
dfa60aba | 132 | const unsigned char *const *noptable = find_nop_table(); |
3d083395 | 133 | |
d61f82d0 SR |
134 | /* This is running in kstop_machine */ |
135 | ||
136 | ftrace_mcount_set(data); | |
137 | ||
395a59d0 | 138 | ftrace_nop = (unsigned long *)noptable[MCOUNT_INSN_SIZE]; |
dfa60aba | 139 | |
3d083395 SR |
140 | return 0; |
141 | } |