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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
4 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
5 *
6 * Code for replacing ftrace calls with jumps.
7 *
8 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
9 *
10 * Thanks goes to Ingo Molnar, for suggesting the idea.
11 * Mathieu Desnoyers, for suggesting postponing the modifications.
12 * Arjan van de Ven, for keeping me straight, and explaining to me
13 * the dangers of modifying code on the run.
14 */
15#include <linux/uaccess.h>
16#include <linux/ftrace.h>
17#include <linux/string.h>
18#include <linux/init.h>
19#include <linux/io.h>
20#include <linux/kernel.h>
21#include <asm/ftrace.h>
22#include <asm/cacheflush.h>
23#include <asm/unistd.h>
24#include <trace/syscall.h>
25
26#ifdef CONFIG_DYNAMIC_FTRACE
27static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
28
29static unsigned char ftrace_nop[4];
30/*
31 * If we're trying to nop out a call to a function, we instead
32 * place a call to the address after the memory table.
33 *
34 * 8c011060 <a>:
35 * 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1
36 * 8c011062: 22 4f sts.l pr,@-r15
37 * 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0
38 * 8c011066: 2b 41 jmp @r1
39 * 8c011068: 2a 40 lds r0,pr
40 * 8c01106a: 09 00 nop
41 * 8c01106c: 68 24 .word 0x2468 <--- ip
42 * 8c01106e: 1d 8c .word 0x8c1d
43 * 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE
44 *
45 * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
46 * past the _mcount call and continue executing code like normal.
47 */
48static unsigned char *ftrace_nop_replace(unsigned long ip)
49{
50 __raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
51 return ftrace_nop;
52}
53
54static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
55{
56 /* Place the address in the memory table. */
57 __raw_writel(addr, ftrace_replaced_code);
58
59 /*
60 * No locking needed, this must be called via kstop_machine
61 * which in essence is like running on a uniprocessor machine.
62 */
63 return ftrace_replaced_code;
64}
65
66/*
67 * Modifying code must take extra care. On an SMP machine, if
68 * the code being modified is also being executed on another CPU
69 * that CPU will have undefined results and possibly take a GPF.
70 * We use kstop_machine to stop other CPUS from exectuing code.
71 * But this does not stop NMIs from happening. We still need
72 * to protect against that. We separate out the modification of
73 * the code to take care of this.
74 *
75 * Two buffers are added: An IP buffer and a "code" buffer.
76 *
77 * 1) Put the instruction pointer into the IP buffer
78 * and the new code into the "code" buffer.
79 * 2) Wait for any running NMIs to finish and set a flag that says
80 * we are modifying code, it is done in an atomic operation.
81 * 3) Write the code
82 * 4) clear the flag.
83 * 5) Wait for any running NMIs to finish.
84 *
85 * If an NMI is executed, the first thing it does is to call
86 * "ftrace_nmi_enter". This will check if the flag is set to write
87 * and if it is, it will write what is in the IP and "code" buffers.
88 *
89 * The trick is, it does not matter if everyone is writing the same
90 * content to the code location. Also, if a CPU is executing code
91 * it is OK to write to that code location if the contents being written
92 * are the same as what exists.
93 */
94#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
95static atomic_t nmi_running = ATOMIC_INIT(0);
96static int mod_code_status; /* holds return value of text write */
97static void *mod_code_ip; /* holds the IP to write to */
98static void *mod_code_newcode; /* holds the text to write to the IP */
99
100static void clear_mod_flag(void)
101{
102 int old = atomic_read(&nmi_running);
103
104 for (;;) {
105 int new = old & ~MOD_CODE_WRITE_FLAG;
106
107 if (old == new)
108 break;
109
110 old = atomic_cmpxchg(&nmi_running, old, new);
111 }
112}
113
114static void ftrace_mod_code(void)
115{
116 /*
117 * Yes, more than one CPU process can be writing to mod_code_status.
118 * (and the code itself)
119 * But if one were to fail, then they all should, and if one were
120 * to succeed, then they all should.
121 */
122 mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
123 MCOUNT_INSN_SIZE);
124
125 /* if we fail, then kill any new writers */
126 if (mod_code_status)
127 clear_mod_flag();
128}
129
130void arch_ftrace_nmi_enter(void)
131{
132 if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
133 smp_rmb();
134 ftrace_mod_code();
135 }
136 /* Must have previous changes seen before executions */
137 smp_mb();
138}
139
140void arch_ftrace_nmi_exit(void)
141{
142 /* Finish all executions before clearing nmi_running */
143 smp_mb();
144 atomic_dec(&nmi_running);
145}
146
147static void wait_for_nmi_and_set_mod_flag(void)
148{
149 if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
150 return;
151
152 do {
153 cpu_relax();
154 } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
155}
156
157static void wait_for_nmi(void)
158{
159 if (!atomic_read(&nmi_running))
160 return;
161
162 do {
163 cpu_relax();
164 } while (atomic_read(&nmi_running));
165}
166
167static int
168do_ftrace_mod_code(unsigned long ip, void *new_code)
169{
170 mod_code_ip = (void *)ip;
171 mod_code_newcode = new_code;
172
173 /* The buffers need to be visible before we let NMIs write them */
174 smp_mb();
175
176 wait_for_nmi_and_set_mod_flag();
177
178 /* Make sure all running NMIs have finished before we write the code */
179 smp_mb();
180
181 ftrace_mod_code();
182
183 /* Make sure the write happens before clearing the bit */
184 smp_mb();
185
186 clear_mod_flag();
187 wait_for_nmi();
188
189 return mod_code_status;
190}
191
192static int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
193 unsigned char *new_code)
194{
195 unsigned char replaced[MCOUNT_INSN_SIZE];
196
197 /*
198 * Note:
199 * We are paranoid about modifying text, as if a bug was to happen, it
200 * could cause us to read or write to someplace that could cause harm.
201 * Carefully read and modify the code with probe_kernel_*(), and make
202 * sure what we read is what we expected it to be before modifying it.
203 */
204
205 /* read the text we want to modify */
206 if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
207 return -EFAULT;
208
209 /* Make sure it is what we expect it to be */
210 if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
211 return -EINVAL;
212
213 /* replace the text with the new text */
214 if (do_ftrace_mod_code(ip, new_code))
215 return -EPERM;
216
217 flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
218
219 return 0;
220}
221
222int ftrace_update_ftrace_func(ftrace_func_t func)
223{
224 unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET;
225 unsigned char old[MCOUNT_INSN_SIZE], *new;
226
227 memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
228 new = ftrace_call_replace(ip, (unsigned long)func);
229
230 return ftrace_modify_code(ip, old, new);
231}
232
233int ftrace_make_nop(struct module *mod,
234 struct dyn_ftrace *rec, unsigned long addr)
235{
236 unsigned char *new, *old;
237 unsigned long ip = rec->ip;
238
239 old = ftrace_call_replace(ip, addr);
240 new = ftrace_nop_replace(ip);
241
242 return ftrace_modify_code(rec->ip, old, new);
243}
244
245int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
246{
247 unsigned char *new, *old;
248 unsigned long ip = rec->ip;
249
250 old = ftrace_nop_replace(ip);
251 new = ftrace_call_replace(ip, addr);
252
253 return ftrace_modify_code(rec->ip, old, new);
254}
255
256int __init ftrace_dyn_arch_init(void)
257{
258 return 0;
259}
260#endif /* CONFIG_DYNAMIC_FTRACE */
261
262#ifdef CONFIG_FUNCTION_GRAPH_TRACER
263#ifdef CONFIG_DYNAMIC_FTRACE
264extern void ftrace_graph_call(void);
265
266static int ftrace_mod(unsigned long ip, unsigned long old_addr,
267 unsigned long new_addr)
268{
269 unsigned char code[MCOUNT_INSN_SIZE];
270
271 if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
272 return -EFAULT;
273
274 if (old_addr != __raw_readl((unsigned long *)code))
275 return -EINVAL;
276
277 __raw_writel(new_addr, ip);
278 return 0;
279}
280
281int ftrace_enable_ftrace_graph_caller(void)
282{
283 unsigned long ip, old_addr, new_addr;
284
285 ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
286 old_addr = (unsigned long)(&skip_trace);
287 new_addr = (unsigned long)(&ftrace_graph_caller);
288
289 return ftrace_mod(ip, old_addr, new_addr);
290}
291
292int ftrace_disable_ftrace_graph_caller(void)
293{
294 unsigned long ip, old_addr, new_addr;
295
296 ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
297 old_addr = (unsigned long)(&ftrace_graph_caller);
298 new_addr = (unsigned long)(&skip_trace);
299
300 return ftrace_mod(ip, old_addr, new_addr);
301}
302#endif /* CONFIG_DYNAMIC_FTRACE */
303
304/*
305 * Hook the return address and push it in the stack of return addrs
306 * in the current thread info.
307 *
308 * This is the main routine for the function graph tracer. The function
309 * graph tracer essentially works like this:
310 *
311 * parent is the stack address containing self_addr's return address.
312 * We pull the real return address out of parent and store it in
313 * current's ret_stack. Then, we replace the return address on the stack
314 * with the address of return_to_handler. self_addr is the function that
315 * called mcount.
316 *
317 * When self_addr returns, it will jump to return_to_handler which calls
318 * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
319 * return address off of current's ret_stack and jump to it.
320 */
321void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
322{
323 unsigned long old;
324 int faulted;
325 unsigned long return_hooker = (unsigned long)&return_to_handler;
326
327 if (unlikely(ftrace_graph_is_dead()))
328 return;
329
330 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
331 return;
332
333 /*
334 * Protect against fault, even if it shouldn't
335 * happen. This tool is too much intrusive to
336 * ignore such a protection.
337 */
338 __asm__ __volatile__(
339 "1: \n\t"
340 "mov.l @%2, %0 \n\t"
341 "2: \n\t"
342 "mov.l %3, @%2 \n\t"
343 "mov #0, %1 \n\t"
344 "3: \n\t"
345 ".section .fixup, \"ax\" \n\t"
346 "4: \n\t"
347 "mov.l 5f, %0 \n\t"
348 "jmp @%0 \n\t"
349 " mov #1, %1 \n\t"
350 ".balign 4 \n\t"
351 "5: .long 3b \n\t"
352 ".previous \n\t"
353 ".section __ex_table,\"a\" \n\t"
354 ".long 1b, 4b \n\t"
355 ".long 2b, 4b \n\t"
356 ".previous \n\t"
357 : "=&r" (old), "=r" (faulted)
358 : "r" (parent), "r" (return_hooker)
359 );
360
361 if (unlikely(faulted)) {
362 ftrace_graph_stop();
363 WARN_ON(1);
364 return;
365 }
366
367 if (function_graph_enter(old, self_addr, 0, NULL))
368 __raw_writel(old, parent);
369}
370#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:
216 * We are paranoid about modifying text, as if a bug was to happen, it
217 * could cause us to read or write to someplace that could cause harm.
218 * Carefully read and modify the code with probe_kernel_*(), and make
219 * sure what we read is what we expected it to be before modifying it.
220 */
221
222 /* read the text we want to modify */
223 if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
224 return -EFAULT;
225
226 /* Make sure it is what we expect it to be */
227 if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
228 return -EINVAL;
229
230 /* replace the text with the new text */
231 if (do_ftrace_mod_code(ip, new_code))
232 return -EPERM;
233
234 flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
235
236 return 0;
237}
238
239int ftrace_update_ftrace_func(ftrace_func_t func)
240{
241 unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET;
242 unsigned char old[MCOUNT_INSN_SIZE], *new;
243
244 memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
245 new = ftrace_call_replace(ip, (unsigned long)func);
246
247 return ftrace_modify_code(ip, old, new);
248}
249
250int ftrace_make_nop(struct module *mod,
251 struct dyn_ftrace *rec, unsigned long addr)
252{
253 unsigned char *new, *old;
254 unsigned long ip = rec->ip;
255
256 old = ftrace_call_replace(ip, addr);
257 new = ftrace_nop_replace(ip);
258
259 return ftrace_modify_code(rec->ip, old, new);
260}
261
262int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
263{
264 unsigned char *new, *old;
265 unsigned long ip = rec->ip;
266
267 old = ftrace_nop_replace(ip);
268 new = ftrace_call_replace(ip, addr);
269
270 return ftrace_modify_code(rec->ip, old, new);
271}
272
273int __init ftrace_dyn_arch_init(void)
274{
275 return 0;
276}
277#endif /* CONFIG_DYNAMIC_FTRACE */
278
279#ifdef CONFIG_FUNCTION_GRAPH_TRACER
280#ifdef CONFIG_DYNAMIC_FTRACE
281extern void ftrace_graph_call(void);
282
283static int ftrace_mod(unsigned long ip, unsigned long old_addr,
284 unsigned long new_addr)
285{
286 unsigned char code[MCOUNT_INSN_SIZE];
287
288 if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
289 return -EFAULT;
290
291 if (old_addr != __raw_readl((unsigned long *)code))
292 return -EINVAL;
293
294 __raw_writel(new_addr, ip);
295 return 0;
296}
297
298int ftrace_enable_ftrace_graph_caller(void)
299{
300 unsigned long ip, old_addr, new_addr;
301
302 ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
303 old_addr = (unsigned long)(&skip_trace);
304 new_addr = (unsigned long)(&ftrace_graph_caller);
305
306 return ftrace_mod(ip, old_addr, new_addr);
307}
308
309int ftrace_disable_ftrace_graph_caller(void)
310{
311 unsigned long ip, old_addr, new_addr;
312
313 ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
314 old_addr = (unsigned long)(&ftrace_graph_caller);
315 new_addr = (unsigned long)(&skip_trace);
316
317 return ftrace_mod(ip, old_addr, new_addr);
318}
319#endif /* CONFIG_DYNAMIC_FTRACE */
320
321/*
322 * Hook the return address and push it in the stack of return addrs
323 * in the current thread info.
324 *
325 * This is the main routine for the function graph tracer. The function
326 * graph tracer essentially works like this:
327 *
328 * parent is the stack address containing self_addr's return address.
329 * We pull the real return address out of parent and store it in
330 * current's ret_stack. Then, we replace the return address on the stack
331 * with the address of return_to_handler. self_addr is the function that
332 * called mcount.
333 *
334 * When self_addr returns, it will jump to return_to_handler which calls
335 * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
336 * return address off of current's ret_stack and jump to it.
337 */
338void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
339{
340 unsigned long old;
341 int faulted, err;
342 struct ftrace_graph_ent trace;
343 unsigned long return_hooker = (unsigned long)&return_to_handler;
344
345 if (unlikely(ftrace_graph_is_dead()))
346 return;
347
348 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
349 return;
350
351 /*
352 * Protect against fault, even if it shouldn't
353 * happen. This tool is too much intrusive to
354 * ignore such a protection.
355 */
356 __asm__ __volatile__(
357 "1: \n\t"
358 "mov.l @%2, %0 \n\t"
359 "2: \n\t"
360 "mov.l %3, @%2 \n\t"
361 "mov #0, %1 \n\t"
362 "3: \n\t"
363 ".section .fixup, \"ax\" \n\t"
364 "4: \n\t"
365 "mov.l 5f, %0 \n\t"
366 "jmp @%0 \n\t"
367 " mov #1, %1 \n\t"
368 ".balign 4 \n\t"
369 "5: .long 3b \n\t"
370 ".previous \n\t"
371 ".section __ex_table,\"a\" \n\t"
372 ".long 1b, 4b \n\t"
373 ".long 2b, 4b \n\t"
374 ".previous \n\t"
375 : "=&r" (old), "=r" (faulted)
376 : "r" (parent), "r" (return_hooker)
377 );
378
379 if (unlikely(faulted)) {
380 ftrace_graph_stop();
381 WARN_ON(1);
382 return;
383 }
384
385 err = ftrace_push_return_trace(old, self_addr, &trace.depth, 0);
386 if (err == -EBUSY) {
387 __raw_writel(old, parent);
388 return;
389 }
390
391 trace.func = self_addr;
392
393 /* Only trace if the calling function expects to */
394 if (!ftrace_graph_entry(&trace)) {
395 current->curr_ret_stack--;
396 __raw_writel(old, parent);
397 }
398}
399#endif /* CONFIG_FUNCTION_GRAPH_TRACER */