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1/*
2 * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
3 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
4 *
5 * Code for replacing ftrace calls with jumps.
6 *
7 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
8 *
9 * Thanks goes to Ingo Molnar, for suggesting the idea.
10 * Mathieu Desnoyers, for suggesting postponing the modifications.
11 * Arjan van de Ven, for keeping me straight, and explaining to me
12 * the dangers of modifying code on the run.
13 */
14#include <linux/uaccess.h>
15#include <linux/ftrace.h>
16#include <linux/string.h>
17#include <linux/init.h>
18#include <linux/io.h>
19#include <linux/kernel.h>
20#include <asm/ftrace.h>
21#include <asm/cacheflush.h>
22#include <asm/unistd.h>
23#include <trace/syscall.h>
24
25#ifdef CONFIG_DYNAMIC_FTRACE
26static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
27
28static unsigned char ftrace_nop[4];
29/*
30 * If we're trying to nop out a call to a function, we instead
31 * place a call to the address after the memory table.
32 *
33 * 8c011060 <a>:
34 * 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1
35 * 8c011062: 22 4f sts.l pr,@-r15
36 * 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0
37 * 8c011066: 2b 41 jmp @r1
38 * 8c011068: 2a 40 lds r0,pr
39 * 8c01106a: 09 00 nop
40 * 8c01106c: 68 24 .word 0x2468 <--- ip
41 * 8c01106e: 1d 8c .word 0x8c1d
42 * 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE
43 *
44 * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
45 * past the _mcount call and continue executing code like normal.
46 */
47static unsigned char *ftrace_nop_replace(unsigned long ip)
48{
49 __raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
50 return ftrace_nop;
51}
52
53static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
54{
55 /* Place the address in the memory table. */
56 __raw_writel(addr, ftrace_replaced_code);
57
58 /*
59 * No locking needed, this must be called via kstop_machine
60 * which in essence is like running on a uniprocessor machine.
61 */
62 return ftrace_replaced_code;
63}
64
65/*
66 * Modifying code must take extra care. On an SMP machine, if
67 * the code being modified is also being executed on another CPU
68 * that CPU will have undefined results and possibly take a GPF.
69 * We use kstop_machine to stop other CPUS from exectuing code.
70 * But this does not stop NMIs from happening. We still need
71 * to protect against that. We separate out the modification of
72 * the code to take care of this.
73 *
74 * Two buffers are added: An IP buffer and a "code" buffer.
75 *
76 * 1) Put the instruction pointer into the IP buffer
77 * and the new code into the "code" buffer.
78 * 2) Wait for any running NMIs to finish and set a flag that says
79 * we are modifying code, it is done in an atomic operation.
80 * 3) Write the code
81 * 4) clear the flag.
82 * 5) Wait for any running NMIs to finish.
83 *
84 * If an NMI is executed, the first thing it does is to call
85 * "ftrace_nmi_enter". This will check if the flag is set to write
86 * and if it is, it will write what is in the IP and "code" buffers.
87 *
88 * The trick is, it does not matter if everyone is writing the same
89 * content to the code location. Also, if a CPU is executing code
90 * it is OK to write to that code location if the contents being written
91 * are the same as what exists.
92 */
93#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
94static atomic_t nmi_running = ATOMIC_INIT(0);
95static int mod_code_status; /* holds return value of text write */
96static void *mod_code_ip; /* holds the IP to write to */
97static void *mod_code_newcode; /* holds the text to write to the IP */
98
99static unsigned nmi_wait_count;
100static atomic_t nmi_update_count = ATOMIC_INIT(0);
101
102int ftrace_arch_read_dyn_info(char *buf, int size)
103{
104 int r;
105
106 r = snprintf(buf, size, "%u %u",
107 nmi_wait_count,
108 atomic_read(&nmi_update_count));
109 return r;
110}
111
112static void clear_mod_flag(void)
113{
114 int old = atomic_read(&nmi_running);
115
116 for (;;) {
117 int new = old & ~MOD_CODE_WRITE_FLAG;
118
119 if (old == new)
120 break;
121
122 old = atomic_cmpxchg(&nmi_running, old, new);
123 }
124}
125
126static void ftrace_mod_code(void)
127{
128 /*
129 * Yes, more than one CPU process can be writing to mod_code_status.
130 * (and the code itself)
131 * But if one were to fail, then they all should, and if one were
132 * to succeed, then they all should.
133 */
134 mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
135 MCOUNT_INSN_SIZE);
136
137 /* if we fail, then kill any new writers */
138 if (mod_code_status)
139 clear_mod_flag();
140}
141
142void ftrace_nmi_enter(void)
143{
144 if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
145 smp_rmb();
146 ftrace_mod_code();
147 atomic_inc(&nmi_update_count);
148 }
149 /* Must have previous changes seen before executions */
150 smp_mb();
151}
152
153void ftrace_nmi_exit(void)
154{
155 /* Finish all executions before clearing nmi_running */
156 smp_mb();
157 atomic_dec(&nmi_running);
158}
159
160static void wait_for_nmi_and_set_mod_flag(void)
161{
162 if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
163 return;
164
165 do {
166 cpu_relax();
167 } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
168
169 nmi_wait_count++;
170}
171
172static void wait_for_nmi(void)
173{
174 if (!atomic_read(&nmi_running))
175 return;
176
177 do {
178 cpu_relax();
179 } while (atomic_read(&nmi_running));
180
181 nmi_wait_count++;
182}
183
184static int
185do_ftrace_mod_code(unsigned long ip, void *new_code)
186{
187 mod_code_ip = (void *)ip;
188 mod_code_newcode = new_code;
189
190 /* The buffers need to be visible before we let NMIs write them */
191 smp_mb();
192
193 wait_for_nmi_and_set_mod_flag();
194
195 /* Make sure all running NMIs have finished before we write the code */
196 smp_mb();
197
198 ftrace_mod_code();
199
200 /* Make sure the write happens before clearing the bit */
201 smp_mb();
202
203 clear_mod_flag();
204 wait_for_nmi();
205
206 return mod_code_status;
207}
208
209static int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
210 unsigned char *new_code)
211{
212 unsigned char replaced[MCOUNT_INSN_SIZE];
213
214 /*
215 * Note: Due to modules and __init, code can
216 * disappear and change, we need to protect against faulting
217 * as well as code changing. We do this by using the
218 * probe_kernel_* functions.
219 *
220 * No real locking needed, this code is run through
221 * kstop_machine, or before SMP starts.
222 */
223
224 /* read the text we want to modify */
225 if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
226 return -EFAULT;
227
228 /* Make sure it is what we expect it to be */
229 if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
230 return -EINVAL;
231
232 /* replace the text with the new text */
233 if (do_ftrace_mod_code(ip, new_code))
234 return -EPERM;
235
236 flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
237
238 return 0;
239}
240
241int ftrace_update_ftrace_func(ftrace_func_t func)
242{
243 unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET;
244 unsigned char old[MCOUNT_INSN_SIZE], *new;
245
246 memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
247 new = ftrace_call_replace(ip, (unsigned long)func);
248
249 return ftrace_modify_code(ip, old, new);
250}
251
252int ftrace_make_nop(struct module *mod,
253 struct dyn_ftrace *rec, unsigned long addr)
254{
255 unsigned char *new, *old;
256 unsigned long ip = rec->ip;
257
258 old = ftrace_call_replace(ip, addr);
259 new = ftrace_nop_replace(ip);
260
261 return ftrace_modify_code(rec->ip, old, new);
262}
263
264int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
265{
266 unsigned char *new, *old;
267 unsigned long ip = rec->ip;
268
269 old = ftrace_nop_replace(ip);
270 new = ftrace_call_replace(ip, addr);
271
272 return ftrace_modify_code(rec->ip, old, new);
273}
274
275int __init ftrace_dyn_arch_init(void)
276{
277 return 0;
278}
279#endif /* CONFIG_DYNAMIC_FTRACE */
280
281#ifdef CONFIG_FUNCTION_GRAPH_TRACER
282#ifdef CONFIG_DYNAMIC_FTRACE
283extern void ftrace_graph_call(void);
284
285static int ftrace_mod(unsigned long ip, unsigned long old_addr,
286 unsigned long new_addr)
287{
288 unsigned char code[MCOUNT_INSN_SIZE];
289
290 if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
291 return -EFAULT;
292
293 if (old_addr != __raw_readl((unsigned long *)code))
294 return -EINVAL;
295
296 __raw_writel(new_addr, ip);
297 return 0;
298}
299
300int ftrace_enable_ftrace_graph_caller(void)
301{
302 unsigned long ip, old_addr, new_addr;
303
304 ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
305 old_addr = (unsigned long)(&skip_trace);
306 new_addr = (unsigned long)(&ftrace_graph_caller);
307
308 return ftrace_mod(ip, old_addr, new_addr);
309}
310
311int ftrace_disable_ftrace_graph_caller(void)
312{
313 unsigned long ip, old_addr, new_addr;
314
315 ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
316 old_addr = (unsigned long)(&ftrace_graph_caller);
317 new_addr = (unsigned long)(&skip_trace);
318
319 return ftrace_mod(ip, old_addr, new_addr);
320}
321#endif /* CONFIG_DYNAMIC_FTRACE */
322
323/*
324 * Hook the return address and push it in the stack of return addrs
325 * in the current thread info.
326 *
327 * This is the main routine for the function graph tracer. The function
328 * graph tracer essentially works like this:
329 *
330 * parent is the stack address containing self_addr's return address.
331 * We pull the real return address out of parent and store it in
332 * current's ret_stack. Then, we replace the return address on the stack
333 * with the address of return_to_handler. self_addr is the function that
334 * called mcount.
335 *
336 * When self_addr returns, it will jump to return_to_handler which calls
337 * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
338 * return address off of current's ret_stack and jump to it.
339 */
340void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
341{
342 unsigned long old;
343 int faulted, err;
344 struct ftrace_graph_ent trace;
345 unsigned long return_hooker = (unsigned long)&return_to_handler;
346
347 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
348 return;
349
350 /*
351 * Protect against fault, even if it shouldn't
352 * happen. This tool is too much intrusive to
353 * ignore such a protection.
354 */
355 __asm__ __volatile__(
356 "1: \n\t"
357 "mov.l @%2, %0 \n\t"
358 "2: \n\t"
359 "mov.l %3, @%2 \n\t"
360 "mov #0, %1 \n\t"
361 "3: \n\t"
362 ".section .fixup, \"ax\" \n\t"
363 "4: \n\t"
364 "mov.l 5f, %0 \n\t"
365 "jmp @%0 \n\t"
366 " mov #1, %1 \n\t"
367 ".balign 4 \n\t"
368 "5: .long 3b \n\t"
369 ".previous \n\t"
370 ".section __ex_table,\"a\" \n\t"
371 ".long 1b, 4b \n\t"
372 ".long 2b, 4b \n\t"
373 ".previous \n\t"
374 : "=&r" (old), "=r" (faulted)
375 : "r" (parent), "r" (return_hooker)
376 );
377
378 if (unlikely(faulted)) {
379 ftrace_graph_stop();
380 WARN_ON(1);
381 return;
382 }
383
384 err = ftrace_push_return_trace(old, self_addr, &trace.depth, 0);
385 if (err == -EBUSY) {
386 __raw_writel(old, parent);
387 return;
388 }
389
390 trace.func = self_addr;
391
392 /* Only trace if the calling function expects to */
393 if (!ftrace_graph_entry(&trace)) {
394 current->curr_ret_stack--;
395 __raw_writel(old, parent);
396 }
397}
398#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
1/*
2 * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
3 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
4 *
5 * Code for replacing ftrace calls with jumps.
6 *
7 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
8 *
9 * Thanks goes to Ingo Molnar, for suggesting the idea.
10 * Mathieu Desnoyers, for suggesting postponing the modifications.
11 * Arjan van de Ven, for keeping me straight, and explaining to me
12 * the dangers of modifying code on the run.
13 */
14#include <linux/uaccess.h>
15#include <linux/ftrace.h>
16#include <linux/string.h>
17#include <linux/init.h>
18#include <linux/io.h>
19#include <linux/kernel.h>
20#include <asm/ftrace.h>
21#include <asm/cacheflush.h>
22#include <asm/unistd.h>
23#include <trace/syscall.h>
24
25#ifdef CONFIG_DYNAMIC_FTRACE
26static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
27
28static unsigned char ftrace_nop[4];
29/*
30 * If we're trying to nop out a call to a function, we instead
31 * place a call to the address after the memory table.
32 *
33 * 8c011060 <a>:
34 * 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1
35 * 8c011062: 22 4f sts.l pr,@-r15
36 * 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0
37 * 8c011066: 2b 41 jmp @r1
38 * 8c011068: 2a 40 lds r0,pr
39 * 8c01106a: 09 00 nop
40 * 8c01106c: 68 24 .word 0x2468 <--- ip
41 * 8c01106e: 1d 8c .word 0x8c1d
42 * 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE
43 *
44 * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
45 * past the _mcount call and continue executing code like normal.
46 */
47static unsigned char *ftrace_nop_replace(unsigned long ip)
48{
49 __raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
50 return ftrace_nop;
51}
52
53static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
54{
55 /* Place the address in the memory table. */
56 __raw_writel(addr, ftrace_replaced_code);
57
58 /*
59 * No locking needed, this must be called via kstop_machine
60 * which in essence is like running on a uniprocessor machine.
61 */
62 return ftrace_replaced_code;
63}
64
65/*
66 * Modifying code must take extra care. On an SMP machine, if
67 * the code being modified is also being executed on another CPU
68 * that CPU will have undefined results and possibly take a GPF.
69 * We use kstop_machine to stop other CPUS from exectuing code.
70 * But this does not stop NMIs from happening. We still need
71 * to protect against that. We separate out the modification of
72 * the code to take care of this.
73 *
74 * Two buffers are added: An IP buffer and a "code" buffer.
75 *
76 * 1) Put the instruction pointer into the IP buffer
77 * and the new code into the "code" buffer.
78 * 2) Wait for any running NMIs to finish and set a flag that says
79 * we are modifying code, it is done in an atomic operation.
80 * 3) Write the code
81 * 4) clear the flag.
82 * 5) Wait for any running NMIs to finish.
83 *
84 * If an NMI is executed, the first thing it does is to call
85 * "ftrace_nmi_enter". This will check if the flag is set to write
86 * and if it is, it will write what is in the IP and "code" buffers.
87 *
88 * The trick is, it does not matter if everyone is writing the same
89 * content to the code location. Also, if a CPU is executing code
90 * it is OK to write to that code location if the contents being written
91 * are the same as what exists.
92 */
93#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
94static atomic_t nmi_running = ATOMIC_INIT(0);
95static int mod_code_status; /* holds return value of text write */
96static void *mod_code_ip; /* holds the IP to write to */
97static void *mod_code_newcode; /* holds the text to write to the IP */
98
99static unsigned nmi_wait_count;
100static atomic_t nmi_update_count = ATOMIC_INIT(0);
101
102int ftrace_arch_read_dyn_info(char *buf, int size)
103{
104 int r;
105
106 r = snprintf(buf, size, "%u %u",
107 nmi_wait_count,
108 atomic_read(&nmi_update_count));
109 return r;
110}
111
112static void clear_mod_flag(void)
113{
114 int old = atomic_read(&nmi_running);
115
116 for (;;) {
117 int new = old & ~MOD_CODE_WRITE_FLAG;
118
119 if (old == new)
120 break;
121
122 old = atomic_cmpxchg(&nmi_running, old, new);
123 }
124}
125
126static void ftrace_mod_code(void)
127{
128 /*
129 * Yes, more than one CPU process can be writing to mod_code_status.
130 * (and the code itself)
131 * But if one were to fail, then they all should, and if one were
132 * to succeed, then they all should.
133 */
134 mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
135 MCOUNT_INSN_SIZE);
136
137 /* if we fail, then kill any new writers */
138 if (mod_code_status)
139 clear_mod_flag();
140}
141
142void ftrace_nmi_enter(void)
143{
144 if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
145 smp_rmb();
146 ftrace_mod_code();
147 atomic_inc(&nmi_update_count);
148 }
149 /* Must have previous changes seen before executions */
150 smp_mb();
151}
152
153void ftrace_nmi_exit(void)
154{
155 /* Finish all executions before clearing nmi_running */
156 smp_mb();
157 atomic_dec(&nmi_running);
158}
159
160static void wait_for_nmi_and_set_mod_flag(void)
161{
162 if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
163 return;
164
165 do {
166 cpu_relax();
167 } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
168
169 nmi_wait_count++;
170}
171
172static void wait_for_nmi(void)
173{
174 if (!atomic_read(&nmi_running))
175 return;
176
177 do {
178 cpu_relax();
179 } while (atomic_read(&nmi_running));
180
181 nmi_wait_count++;
182}
183
184static int
185do_ftrace_mod_code(unsigned long ip, void *new_code)
186{
187 mod_code_ip = (void *)ip;
188 mod_code_newcode = new_code;
189
190 /* The buffers need to be visible before we let NMIs write them */
191 smp_mb();
192
193 wait_for_nmi_and_set_mod_flag();
194
195 /* Make sure all running NMIs have finished before we write the code */
196 smp_mb();
197
198 ftrace_mod_code();
199
200 /* Make sure the write happens before clearing the bit */
201 smp_mb();
202
203 clear_mod_flag();
204 wait_for_nmi();
205
206 return mod_code_status;
207}
208
209static int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
210 unsigned char *new_code)
211{
212 unsigned char replaced[MCOUNT_INSN_SIZE];
213
214 /*
215 * Note: Due to modules and __init, code can
216 * disappear and change, we need to protect against faulting
217 * as well as code changing. We do this by using the
218 * probe_kernel_* functions.
219 *
220 * No real locking needed, this code is run through
221 * kstop_machine, or before SMP starts.
222 */
223
224 /* read the text we want to modify */
225 if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
226 return -EFAULT;
227
228 /* Make sure it is what we expect it to be */
229 if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
230 return -EINVAL;
231
232 /* replace the text with the new text */
233 if (do_ftrace_mod_code(ip, new_code))
234 return -EPERM;
235
236 flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
237
238 return 0;
239}
240
241int ftrace_update_ftrace_func(ftrace_func_t func)
242{
243 unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET;
244 unsigned char old[MCOUNT_INSN_SIZE], *new;
245
246 memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
247 new = ftrace_call_replace(ip, (unsigned long)func);
248
249 return ftrace_modify_code(ip, old, new);
250}
251
252int ftrace_make_nop(struct module *mod,
253 struct dyn_ftrace *rec, unsigned long addr)
254{
255 unsigned char *new, *old;
256 unsigned long ip = rec->ip;
257
258 old = ftrace_call_replace(ip, addr);
259 new = ftrace_nop_replace(ip);
260
261 return ftrace_modify_code(rec->ip, old, new);
262}
263
264int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
265{
266 unsigned char *new, *old;
267 unsigned long ip = rec->ip;
268
269 old = ftrace_nop_replace(ip);
270 new = ftrace_call_replace(ip, addr);
271
272 return ftrace_modify_code(rec->ip, old, new);
273}
274
275int __init ftrace_dyn_arch_init(void *data)
276{
277 /* The return code is retured via data */
278 __raw_writel(0, (unsigned long)data);
279
280 return 0;
281}
282#endif /* CONFIG_DYNAMIC_FTRACE */
283
284#ifdef CONFIG_FUNCTION_GRAPH_TRACER
285#ifdef CONFIG_DYNAMIC_FTRACE
286extern void ftrace_graph_call(void);
287
288static int ftrace_mod(unsigned long ip, unsigned long old_addr,
289 unsigned long new_addr)
290{
291 unsigned char code[MCOUNT_INSN_SIZE];
292
293 if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
294 return -EFAULT;
295
296 if (old_addr != __raw_readl((unsigned long *)code))
297 return -EINVAL;
298
299 __raw_writel(new_addr, ip);
300 return 0;
301}
302
303int ftrace_enable_ftrace_graph_caller(void)
304{
305 unsigned long ip, old_addr, new_addr;
306
307 ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
308 old_addr = (unsigned long)(&skip_trace);
309 new_addr = (unsigned long)(&ftrace_graph_caller);
310
311 return ftrace_mod(ip, old_addr, new_addr);
312}
313
314int ftrace_disable_ftrace_graph_caller(void)
315{
316 unsigned long ip, old_addr, new_addr;
317
318 ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
319 old_addr = (unsigned long)(&ftrace_graph_caller);
320 new_addr = (unsigned long)(&skip_trace);
321
322 return ftrace_mod(ip, old_addr, new_addr);
323}
324#endif /* CONFIG_DYNAMIC_FTRACE */
325
326/*
327 * Hook the return address and push it in the stack of return addrs
328 * in the current thread info.
329 *
330 * This is the main routine for the function graph tracer. The function
331 * graph tracer essentially works like this:
332 *
333 * parent is the stack address containing self_addr's return address.
334 * We pull the real return address out of parent and store it in
335 * current's ret_stack. Then, we replace the return address on the stack
336 * with the address of return_to_handler. self_addr is the function that
337 * called mcount.
338 *
339 * When self_addr returns, it will jump to return_to_handler which calls
340 * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
341 * return address off of current's ret_stack and jump to it.
342 */
343void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
344{
345 unsigned long old;
346 int faulted, err;
347 struct ftrace_graph_ent trace;
348 unsigned long return_hooker = (unsigned long)&return_to_handler;
349
350 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
351 return;
352
353 /*
354 * Protect against fault, even if it shouldn't
355 * happen. This tool is too much intrusive to
356 * ignore such a protection.
357 */
358 __asm__ __volatile__(
359 "1: \n\t"
360 "mov.l @%2, %0 \n\t"
361 "2: \n\t"
362 "mov.l %3, @%2 \n\t"
363 "mov #0, %1 \n\t"
364 "3: \n\t"
365 ".section .fixup, \"ax\" \n\t"
366 "4: \n\t"
367 "mov.l 5f, %0 \n\t"
368 "jmp @%0 \n\t"
369 " mov #1, %1 \n\t"
370 ".balign 4 \n\t"
371 "5: .long 3b \n\t"
372 ".previous \n\t"
373 ".section __ex_table,\"a\" \n\t"
374 ".long 1b, 4b \n\t"
375 ".long 2b, 4b \n\t"
376 ".previous \n\t"
377 : "=&r" (old), "=r" (faulted)
378 : "r" (parent), "r" (return_hooker)
379 );
380
381 if (unlikely(faulted)) {
382 ftrace_graph_stop();
383 WARN_ON(1);
384 return;
385 }
386
387 err = ftrace_push_return_trace(old, self_addr, &trace.depth, 0);
388 if (err == -EBUSY) {
389 __raw_writel(old, parent);
390 return;
391 }
392
393 trace.func = self_addr;
394
395 /* Only trace if the calling function expects to */
396 if (!ftrace_graph_entry(&trace)) {
397 current->curr_ret_stack--;
398 __raw_writel(old, parent);
399 }
400}
401#endif /* CONFIG_FUNCTION_GRAPH_TRACER */