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> | |
6f93fc07 | 14 | #include <linux/uaccess.h> |
3d083395 SR |
15 | #include <linux/ftrace.h> |
16 | #include <linux/percpu.h> | |
17 | #include <linux/init.h> | |
18 | #include <linux/list.h> | |
19 | ||
395a59d0 | 20 | #include <asm/ftrace.h> |
732f3ca7 | 21 | #include <asm/nops.h> |
3d083395 | 22 | |
3d083395 | 23 | |
dfa60aba | 24 | /* Long is fine, even if it is only 4 bytes ;-) */ |
37a52f5e | 25 | static unsigned long *ftrace_nop; |
3d083395 | 26 | |
3d083395 | 27 | union ftrace_code_union { |
395a59d0 | 28 | char code[MCOUNT_INSN_SIZE]; |
3d083395 SR |
29 | struct { |
30 | char e8; | |
31 | int offset; | |
32 | } __attribute__((packed)); | |
33 | }; | |
34 | ||
395a59d0 | 35 | |
3c1720f0 SR |
36 | static int notrace ftrace_calc_offset(long ip, long addr) |
37 | { | |
38 | return (int)(addr - ip); | |
39 | } | |
3d083395 | 40 | |
3c1720f0 SR |
41 | notrace unsigned char *ftrace_nop_replace(void) |
42 | { | |
43 | return (char *)ftrace_nop; | |
44 | } | |
45 | ||
46 | notrace unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) | |
47 | { | |
48 | static union ftrace_code_union calc; | |
3d083395 | 49 | |
3c1720f0 | 50 | calc.e8 = 0xe8; |
395a59d0 | 51 | calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr); |
3c1720f0 SR |
52 | |
53 | /* | |
54 | * No locking needed, this must be called via kstop_machine | |
55 | * which in essence is like running on a uniprocessor machine. | |
56 | */ | |
57 | return calc.code; | |
3d083395 SR |
58 | } |
59 | ||
3c1720f0 | 60 | notrace int |
3d083395 SR |
61 | ftrace_modify_code(unsigned long ip, unsigned char *old_code, |
62 | unsigned char *new_code) | |
63 | { | |
6f93fc07 | 64 | unsigned char replaced[MCOUNT_INSN_SIZE]; |
c5138675 | 65 | int ret; |
3d083395 SR |
66 | |
67 | /* | |
68 | * Note: Due to modules and __init, code can | |
69 | * disappear and change, we need to protect against faulting | |
70 | * as well as code changing. | |
71 | * | |
72 | * No real locking needed, this code is run through | |
6f93fc07 | 73 | * kstop_machine, or before SMP starts. |
3d083395 | 74 | */ |
ac2b86fd | 75 | if (__copy_from_user_inatomic(replaced, (char __user *)ip, MCOUNT_INSN_SIZE)) |
6f93fc07 SR |
76 | return 1; |
77 | ||
78 | if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0) | |
79 | return 2; | |
3d083395 | 80 | |
c5138675 SR |
81 | ret = __copy_to_user_inatomic((char __user *)ip, new_code, |
82 | MCOUNT_INSN_SIZE); | |
83 | WARN_ON_ONCE(ret); | |
6f93fc07 SR |
84 | |
85 | sync_core(); | |
3d083395 | 86 | |
6f93fc07 | 87 | return 0; |
3d083395 SR |
88 | } |
89 | ||
d61f82d0 SR |
90 | notrace int ftrace_update_ftrace_func(ftrace_func_t func) |
91 | { | |
92 | unsigned long ip = (unsigned long)(&ftrace_call); | |
395a59d0 | 93 | unsigned char old[MCOUNT_INSN_SIZE], *new; |
d61f82d0 SR |
94 | int ret; |
95 | ||
395a59d0 | 96 | memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE); |
d61f82d0 SR |
97 | new = ftrace_call_replace(ip, (unsigned long)func); |
98 | ret = ftrace_modify_code(ip, old, new); | |
99 | ||
100 | return ret; | |
101 | } | |
102 | ||
103 | notrace int ftrace_mcount_set(unsigned long *data) | |
104 | { | |
0a37605c SR |
105 | /* mcount is initialized as a nop */ |
106 | *data = 0; | |
d61f82d0 SR |
107 | return 0; |
108 | } | |
109 | ||
110 | int __init ftrace_dyn_arch_init(void *data) | |
3d083395 | 111 | { |
732f3ca7 SR |
112 | extern const unsigned char ftrace_test_p6nop[]; |
113 | extern const unsigned char ftrace_test_nop5[]; | |
114 | extern const unsigned char ftrace_test_jmp[]; | |
115 | int faulted = 0; | |
d61f82d0 | 116 | |
732f3ca7 SR |
117 | /* |
118 | * There is no good nop for all x86 archs. | |
119 | * We will default to using the P6_NOP5, but first we | |
120 | * will test to make sure that the nop will actually | |
121 | * work on this CPU. If it faults, we will then | |
122 | * go to a lesser efficient 5 byte nop. If that fails | |
123 | * we then just use a jmp as our nop. This isn't the most | |
124 | * efficient nop, but we can not use a multi part nop | |
125 | * since we would then risk being preempted in the middle | |
126 | * of that nop, and if we enabled tracing then, it might | |
127 | * cause a system crash. | |
128 | * | |
129 | * TODO: check the cpuid to determine the best nop. | |
130 | */ | |
131 | asm volatile ( | |
132 | "jmp ftrace_test_jmp\n" | |
133 | /* This code needs to stay around */ | |
134 | ".section .text, \"ax\"\n" | |
135 | "ftrace_test_jmp:" | |
136 | "jmp ftrace_test_p6nop\n" | |
8b27386a AK |
137 | "nop\n" |
138 | "nop\n" | |
139 | "nop\n" /* 2 byte jmp + 3 bytes */ | |
732f3ca7 SR |
140 | "ftrace_test_p6nop:" |
141 | P6_NOP5 | |
142 | "jmp 1f\n" | |
143 | "ftrace_test_nop5:" | |
144 | ".byte 0x66,0x66,0x66,0x66,0x90\n" | |
145 | "jmp 1f\n" | |
146 | ".previous\n" | |
147 | "1:" | |
148 | ".section .fixup, \"ax\"\n" | |
149 | "2: movl $1, %0\n" | |
150 | " jmp ftrace_test_nop5\n" | |
151 | "3: movl $2, %0\n" | |
152 | " jmp 1b\n" | |
153 | ".previous\n" | |
154 | _ASM_EXTABLE(ftrace_test_p6nop, 2b) | |
155 | _ASM_EXTABLE(ftrace_test_nop5, 3b) | |
156 | : "=r"(faulted) : "0" (faulted)); | |
157 | ||
158 | switch (faulted) { | |
159 | case 0: | |
160 | pr_info("ftrace: converting mcount calls to 0f 1f 44 00 00\n"); | |
161 | ftrace_nop = (unsigned long *)ftrace_test_p6nop; | |
162 | break; | |
163 | case 1: | |
164 | pr_info("ftrace: converting mcount calls to 66 66 66 66 90\n"); | |
165 | ftrace_nop = (unsigned long *)ftrace_test_nop5; | |
166 | break; | |
167 | case 2: | |
8b27386a | 168 | pr_info("ftrace: converting mcount calls to jmp . + 5\n"); |
732f3ca7 SR |
169 | ftrace_nop = (unsigned long *)ftrace_test_jmp; |
170 | break; | |
171 | } | |
172 | ||
173 | /* The return code is retured via data */ | |
174 | *(unsigned long *)data = 0; | |
dfa60aba | 175 | |
3d083395 SR |
176 | return 0; |
177 | } |