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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 | 34 | notrace int ftrace_ip_converted(unsigned long ip) |
3d083395 | 35 | { |
dfa60aba | 36 | unsigned long save; |
3d083395 SR |
37 | |
38 | ip -= CALL_BACK; | |
dfa60aba | 39 | save = *(long *)ip; |
3d083395 | 40 | |
3c1720f0 SR |
41 | return save == *ftrace_nop; |
42 | } | |
3d083395 | 43 | |
3c1720f0 SR |
44 | static int notrace ftrace_calc_offset(long ip, long addr) |
45 | { | |
46 | return (int)(addr - ip); | |
47 | } | |
3d083395 | 48 | |
3c1720f0 SR |
49 | notrace unsigned char *ftrace_nop_replace(void) |
50 | { | |
51 | return (char *)ftrace_nop; | |
52 | } | |
53 | ||
54 | notrace unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) | |
55 | { | |
56 | static union ftrace_code_union calc; | |
3d083395 | 57 | |
3c1720f0 SR |
58 | calc.e8 = 0xe8; |
59 | calc.offset = ftrace_calc_offset(ip, addr); | |
60 | ||
61 | /* | |
62 | * No locking needed, this must be called via kstop_machine | |
63 | * which in essence is like running on a uniprocessor machine. | |
64 | */ | |
65 | return calc.code; | |
3d083395 SR |
66 | } |
67 | ||
3c1720f0 | 68 | notrace int |
3d083395 SR |
69 | ftrace_modify_code(unsigned long ip, unsigned char *old_code, |
70 | unsigned char *new_code) | |
71 | { | |
dfa60aba SR |
72 | unsigned replaced; |
73 | unsigned old = *(unsigned *)old_code; /* 4 bytes */ | |
74 | unsigned new = *(unsigned *)new_code; /* 4 bytes */ | |
75 | unsigned char newch = new_code[4]; | |
3d083395 SR |
76 | int faulted = 0; |
77 | ||
3c1720f0 SR |
78 | /* move the IP back to the start of the call */ |
79 | ip -= CALL_BACK; | |
80 | ||
3d083395 SR |
81 | /* |
82 | * Note: Due to modules and __init, code can | |
83 | * disappear and change, we need to protect against faulting | |
84 | * as well as code changing. | |
85 | * | |
86 | * No real locking needed, this code is run through | |
87 | * kstop_machine. | |
88 | */ | |
89 | asm volatile ( | |
90 | "1: lock\n" | |
dfa60aba SR |
91 | " cmpxchg %3, (%2)\n" |
92 | " jnz 2f\n" | |
93 | " movb %b4, 4(%2)\n" | |
3d083395 SR |
94 | "2:\n" |
95 | ".section .fixup, \"ax\"\n" | |
96 | " movl $1, %0\n" | |
97 | "3: jmp 2b\n" | |
98 | ".previous\n" | |
99 | _ASM_EXTABLE(1b, 3b) | |
100 | : "=r"(faulted), "=a"(replaced) | |
dfa60aba SR |
101 | : "r"(ip), "r"(new), "r"(newch), |
102 | "0"(faulted), "a"(old) | |
3d083395 SR |
103 | : "memory"); |
104 | sync_core(); | |
105 | ||
dfa60aba | 106 | if (replaced != old && replaced != new) |
3d083395 SR |
107 | faulted = 2; |
108 | ||
109 | return faulted; | |
110 | } | |
111 | ||
3c1720f0 | 112 | int __init ftrace_dyn_arch_init(void) |
3d083395 | 113 | { |
dfa60aba | 114 | const unsigned char *const *noptable = find_nop_table(); |
3d083395 | 115 | |
dfa60aba SR |
116 | ftrace_nop = (unsigned long *)noptable[CALL_BACK]; |
117 | ||
3d083395 SR |
118 | return 0; |
119 | } | |
3c1720f0 | 120 |