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 | |
8115f3f0 | 24 | static unsigned char ftrace_nop[MCOUNT_INSN_SIZE]; |
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 | |
15adc048 | 35 | static int ftrace_calc_offset(long ip, long addr) |
3c1720f0 SR |
36 | { |
37 | return (int)(addr - ip); | |
38 | } | |
3d083395 | 39 | |
15adc048 | 40 | unsigned char *ftrace_nop_replace(void) |
3c1720f0 | 41 | { |
8115f3f0 | 42 | return ftrace_nop; |
3c1720f0 SR |
43 | } |
44 | ||
15adc048 | 45 | unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) |
3c1720f0 SR |
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 | ||
15adc048 | 59 | int |
3d083395 SR |
60 | ftrace_modify_code(unsigned long ip, unsigned char *old_code, |
61 | unsigned char *new_code) | |
62 | { | |
6f93fc07 | 63 | unsigned char replaced[MCOUNT_INSN_SIZE]; |
3d083395 SR |
64 | |
65 | /* | |
66 | * Note: Due to modules and __init, code can | |
67 | * disappear and change, we need to protect against faulting | |
76aefee5 | 68 | * as well as code changing. We do this by using the |
ab9a0918 | 69 | * probe_kernel_* functions. |
3d083395 SR |
70 | * |
71 | * No real locking needed, this code is run through | |
6f93fc07 | 72 | * kstop_machine, or before SMP starts. |
3d083395 | 73 | */ |
76aefee5 SR |
74 | |
75 | /* read the text we want to modify */ | |
ab9a0918 | 76 | if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE)) |
593eb8a2 | 77 | return -EFAULT; |
6f93fc07 | 78 | |
76aefee5 | 79 | /* Make sure it is what we expect it to be */ |
6f93fc07 | 80 | if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0) |
593eb8a2 | 81 | return -EINVAL; |
3d083395 | 82 | |
76aefee5 | 83 | /* replace the text with the new text */ |
ab9a0918 | 84 | if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE)) |
593eb8a2 | 85 | return -EPERM; |
6f93fc07 SR |
86 | |
87 | sync_core(); | |
3d083395 | 88 | |
6f93fc07 | 89 | return 0; |
3d083395 SR |
90 | } |
91 | ||
15adc048 | 92 | int ftrace_update_ftrace_func(ftrace_func_t func) |
d61f82d0 SR |
93 | { |
94 | unsigned long ip = (unsigned long)(&ftrace_call); | |
395a59d0 | 95 | unsigned char old[MCOUNT_INSN_SIZE], *new; |
d61f82d0 SR |
96 | int ret; |
97 | ||
395a59d0 | 98 | memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE); |
d61f82d0 SR |
99 | new = ftrace_call_replace(ip, (unsigned long)func); |
100 | ret = ftrace_modify_code(ip, old, new); | |
101 | ||
102 | return ret; | |
103 | } | |
104 | ||
d61f82d0 | 105 | int __init ftrace_dyn_arch_init(void *data) |
3d083395 | 106 | { |
732f3ca7 SR |
107 | extern const unsigned char ftrace_test_p6nop[]; |
108 | extern const unsigned char ftrace_test_nop5[]; | |
109 | extern const unsigned char ftrace_test_jmp[]; | |
110 | int faulted = 0; | |
d61f82d0 | 111 | |
732f3ca7 SR |
112 | /* |
113 | * There is no good nop for all x86 archs. | |
114 | * We will default to using the P6_NOP5, but first we | |
115 | * will test to make sure that the nop will actually | |
116 | * work on this CPU. If it faults, we will then | |
117 | * go to a lesser efficient 5 byte nop. If that fails | |
118 | * we then just use a jmp as our nop. This isn't the most | |
119 | * efficient nop, but we can not use a multi part nop | |
120 | * since we would then risk being preempted in the middle | |
121 | * of that nop, and if we enabled tracing then, it might | |
122 | * cause a system crash. | |
123 | * | |
124 | * TODO: check the cpuid to determine the best nop. | |
125 | */ | |
126 | asm volatile ( | |
732f3ca7 SR |
127 | "ftrace_test_jmp:" |
128 | "jmp ftrace_test_p6nop\n" | |
8b27386a AK |
129 | "nop\n" |
130 | "nop\n" | |
131 | "nop\n" /* 2 byte jmp + 3 bytes */ | |
732f3ca7 SR |
132 | "ftrace_test_p6nop:" |
133 | P6_NOP5 | |
134 | "jmp 1f\n" | |
135 | "ftrace_test_nop5:" | |
136 | ".byte 0x66,0x66,0x66,0x66,0x90\n" | |
732f3ca7 SR |
137 | "1:" |
138 | ".section .fixup, \"ax\"\n" | |
139 | "2: movl $1, %0\n" | |
140 | " jmp ftrace_test_nop5\n" | |
141 | "3: movl $2, %0\n" | |
142 | " jmp 1b\n" | |
143 | ".previous\n" | |
144 | _ASM_EXTABLE(ftrace_test_p6nop, 2b) | |
145 | _ASM_EXTABLE(ftrace_test_nop5, 3b) | |
146 | : "=r"(faulted) : "0" (faulted)); | |
147 | ||
148 | switch (faulted) { | |
149 | case 0: | |
150 | pr_info("ftrace: converting mcount calls to 0f 1f 44 00 00\n"); | |
8115f3f0 | 151 | memcpy(ftrace_nop, ftrace_test_p6nop, MCOUNT_INSN_SIZE); |
732f3ca7 SR |
152 | break; |
153 | case 1: | |
154 | pr_info("ftrace: converting mcount calls to 66 66 66 66 90\n"); | |
8115f3f0 | 155 | memcpy(ftrace_nop, ftrace_test_nop5, MCOUNT_INSN_SIZE); |
732f3ca7 SR |
156 | break; |
157 | case 2: | |
8b27386a | 158 | pr_info("ftrace: converting mcount calls to jmp . + 5\n"); |
8115f3f0 | 159 | memcpy(ftrace_nop, ftrace_test_jmp, MCOUNT_INSN_SIZE); |
732f3ca7 SR |
160 | break; |
161 | } | |
162 | ||
163 | /* The return code is retured via data */ | |
164 | *(unsigned long *)data = 0; | |
dfa60aba | 165 | |
3d083395 SR |
166 | return 0; |
167 | } |