Linux Kernel  3.7.1
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ftrace.c
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1 /*
2  * Dynamic function tracing support.
3  *
4  * Copyright (C) 2008 Shaohua Li <[email protected]>
5  *
6  * For licencing details, see COPYING.
7  *
8  * Defines low-level handling of mcount calls when the kernel
9  * is compiled with the -pg flag. When using dynamic ftrace, the
10  * mcount call-sites get patched lazily with NOP till they are
11  * enabled. All code mutation routines here take effect atomically.
12  */
13 
14 #include <linux/uaccess.h>
15 #include <linux/ftrace.h>
16 
17 #include <asm/cacheflush.h>
18 #include <asm/patch.h>
19 
20 /* In IA64, each function will be added below two bundles with -pg option */
21 static unsigned char __attribute__((aligned(8)))
22 ftrace_orig_code[MCOUNT_INSN_SIZE] = {
23  0x02, 0x40, 0x31, 0x10, 0x80, 0x05, /* alloc r40=ar.pfs,12,8,0 */
24  0xb0, 0x02, 0x00, 0x00, 0x42, 0x40, /* mov r43=r0;; */
25  0x05, 0x00, 0xc4, 0x00, /* mov r42=b0 */
26  0x11, 0x48, 0x01, 0x02, 0x00, 0x21, /* mov r41=r1 */
27  0x00, 0x00, 0x00, 0x02, 0x00, 0x00, /* nop.i 0x0 */
28  0x08, 0x00, 0x00, 0x50 /* br.call.sptk.many b0 = _mcount;; */
29 };
30 
33  u64 dummy4:64-41+13;
34  u64 imm20:20;
36  u64 sign:1;
38 };
39 
40 /* mcount stub will be converted below for nop */
41 static unsigned char ftrace_nop_code[MCOUNT_INSN_SIZE] = {
42  0x00, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MII] nop.m 0x0 */
43  0x30, 0x00, 0x00, 0x60, 0x00, 0x00, /* mov r3=ip */
44  0x00, 0x00, 0x04, 0x00, /* nop.i 0x0 */
45  0x05, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MLX] nop.m 0x0 */
46  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* nop.x 0x0;; */
47  0x00, 0x00, 0x04, 0x00
48 };
49 
50 static unsigned char *ftrace_nop_replace(void)
51 {
52  return ftrace_nop_code;
53 }
54 
55 /*
56  * mcount stub will be converted below for call
57  * Note: Just the last instruction is changed against nop
58  * */
59 static unsigned char __attribute__((aligned(8)))
60 ftrace_call_code[MCOUNT_INSN_SIZE] = {
61  0x00, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MII] nop.m 0x0 */
62  0x30, 0x00, 0x00, 0x60, 0x00, 0x00, /* mov r3=ip */
63  0x00, 0x00, 0x04, 0x00, /* nop.i 0x0 */
64  0x05, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MLX] nop.m 0x0 */
65  0xff, 0xff, 0xff, 0xff, 0x7f, 0x00, /* brl.many .;;*/
66  0xf8, 0xff, 0xff, 0xc8
67 };
68 
71  u64 dummy3:48;
74  u64 dummy4:13;
75  u64 imm20:20;
77  u64 i:1;
79 };
80 
81 static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
82 {
83  struct ftrace_call_insn *code = (void *)ftrace_call_code;
84  unsigned long offset = addr - (ip + 0x10);
85 
86  code->imm39_l = offset >> 24;
87  code->imm39_h = offset >> 40;
88  code->imm20 = offset >> 4;
89  code->i = offset >> 63;
90  return ftrace_call_code;
91 }
92 
93 static int
94 ftrace_modify_code(unsigned long ip, unsigned char *old_code,
95  unsigned char *new_code, int do_check)
96 {
97  unsigned char replaced[MCOUNT_INSN_SIZE];
98 
99  /*
100  * Note: Due to modules and __init, code can
101  * disappear and change, we need to protect against faulting
102  * as well as code changing. We do this by using the
103  * probe_kernel_* functions.
104  *
105  * No real locking needed, this code is run through
106  * kstop_machine, or before SMP starts.
107  */
108 
109  if (!do_check)
110  goto skip_check;
111 
112  /* read the text we want to modify */
113  if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
114  return -EFAULT;
115 
116  /* Make sure it is what we expect it to be */
117  if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
118  return -EINVAL;
119 
120 skip_check:
121  /* replace the text with the new text */
122  if (probe_kernel_write(((void *)ip), new_code, MCOUNT_INSN_SIZE))
123  return -EPERM;
125 
126  return 0;
127 }
128 
129 static int ftrace_make_nop_check(struct dyn_ftrace *rec, unsigned long addr)
130 {
131  unsigned char __attribute__((aligned(8))) replaced[MCOUNT_INSN_SIZE];
132  unsigned long ip = rec->ip;
133 
134  if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
135  return -EFAULT;
136  if (rec->flags & FTRACE_FL_CONVERTED) {
137  struct ftrace_call_insn *call_insn, *tmp_call;
138 
139  call_insn = (void *)ftrace_call_code;
140  tmp_call = (void *)replaced;
141  call_insn->imm39_l = tmp_call->imm39_l;
142  call_insn->imm39_h = tmp_call->imm39_h;
143  call_insn->imm20 = tmp_call->imm20;
144  call_insn->i = tmp_call->i;
145  if (memcmp(replaced, ftrace_call_code, MCOUNT_INSN_SIZE) != 0)
146  return -EINVAL;
147  return 0;
148  } else {
149  struct ftrace_orig_insn *call_insn, *tmp_call;
150 
151  call_insn = (void *)ftrace_orig_code;
152  tmp_call = (void *)replaced;
153  call_insn->sign = tmp_call->sign;
154  call_insn->imm20 = tmp_call->imm20;
155  if (memcmp(replaced, ftrace_orig_code, MCOUNT_INSN_SIZE) != 0)
156  return -EINVAL;
157  return 0;
158  }
159 }
160 
162  struct dyn_ftrace *rec, unsigned long addr)
163 {
164  int ret;
165  char *new;
166 
167  ret = ftrace_make_nop_check(rec, addr);
168  if (ret)
169  return ret;
170  new = ftrace_nop_replace();
171  return ftrace_modify_code(rec->ip, NULL, new, 0);
172 }
173 
174 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
175 {
176  unsigned long ip = rec->ip;
177  unsigned char *old, *new;
178 
179  old= ftrace_nop_replace();
180  new = ftrace_call_replace(ip, addr);
181  return ftrace_modify_code(ip, old, new, 1);
182 }
183 
184 /* in IA64, _mcount can't directly call ftrace_stub. Only jump is ok */
185 int ftrace_update_ftrace_func(ftrace_func_t func)
186 {
187  unsigned long ip;
188  unsigned long addr = ((struct fnptr *)ftrace_call)->ip;
189 
190  if (func == ftrace_stub)
191  return 0;
192  ip = ((struct fnptr *)func)->ip;
193 
194  ia64_patch_imm64(addr + 2, ip);
195 
196  flush_icache_range(addr, addr + 16);
197  return 0;
198 }
199 
200 /* run from kstop_machine */
202 {
203  *(unsigned long *)data = 0;
204 
205  return 0;
206 }