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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Code for replacing ftrace calls with jumps.
4 *
5 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
6 * Copyright (C) 2009, 2010 DSLab, Lanzhou University, China
7 * Author: Wu Zhangjin <wuzhangjin@gmail.com>
8 *
9 * Thanks goes to Steven Rostedt for writing the original x86 version.
10 */
11
12#include <linux/uaccess.h>
13#include <linux/init.h>
14#include <linux/ftrace.h>
15#include <linux/syscalls.h>
16
17#include <asm/asm.h>
18#include <asm/asm-offsets.h>
19#include <asm/cacheflush.h>
20#include <asm/syscall.h>
21#include <asm/uasm.h>
22#include <asm/unistd.h>
23
24#include <asm-generic/sections.h>
25
26#if defined(KBUILD_MCOUNT_RA_ADDRESS) && defined(CONFIG_32BIT)
27#define MCOUNT_OFFSET_INSNS 5
28#else
29#define MCOUNT_OFFSET_INSNS 4
30#endif
31
32#ifdef CONFIG_DYNAMIC_FTRACE
33
34/* Arch override because MIPS doesn't need to run this from stop_machine() */
35void arch_ftrace_update_code(int command)
36{
37 ftrace_modify_all_code(command);
38}
39
40#endif
41
42#ifdef CONFIG_DYNAMIC_FTRACE
43
44#define JAL 0x0c000000 /* jump & link: ip --> ra, jump to target */
45#define ADDR_MASK 0x03ffffff /* op_code|addr : 31...26|25 ....0 */
46#define JUMP_RANGE_MASK ((1UL << 28) - 1)
47
48#define INSN_NOP 0x00000000 /* nop */
49#define INSN_JAL(addr) \
50 ((unsigned int)(JAL | (((addr) >> 2) & ADDR_MASK)))
51
52static unsigned int insn_jal_ftrace_caller __read_mostly;
53static unsigned int insn_la_mcount[2] __read_mostly;
54static unsigned int insn_j_ftrace_graph_caller __maybe_unused __read_mostly;
55
56static inline void ftrace_dyn_arch_init_insns(void)
57{
58 u32 *buf;
59 unsigned int v1;
60
61 /* la v1, _mcount */
62 v1 = 3;
63 buf = (u32 *)&insn_la_mcount[0];
64 UASM_i_LA(&buf, v1, MCOUNT_ADDR);
65
66 /* jal (ftrace_caller + 8), jump over the first two instruction */
67 buf = (u32 *)&insn_jal_ftrace_caller;
68 uasm_i_jal(&buf, (FTRACE_ADDR + 8) & JUMP_RANGE_MASK);
69
70#ifdef CONFIG_FUNCTION_GRAPH_TRACER
71 /* j ftrace_graph_caller */
72 buf = (u32 *)&insn_j_ftrace_graph_caller;
73 uasm_i_j(&buf, (unsigned long)ftrace_graph_caller & JUMP_RANGE_MASK);
74#endif
75}
76
77static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
78{
79 int faulted;
80 mm_segment_t old_fs;
81
82 /* *(unsigned int *)ip = new_code; */
83 safe_store_code(new_code, ip, faulted);
84
85 if (unlikely(faulted))
86 return -EFAULT;
87
88 old_fs = get_fs();
89 set_fs(get_ds());
90 flush_icache_range(ip, ip + 8);
91 set_fs(old_fs);
92
93 return 0;
94}
95
96#ifndef CONFIG_64BIT
97static int ftrace_modify_code_2(unsigned long ip, unsigned int new_code1,
98 unsigned int new_code2)
99{
100 int faulted;
101 mm_segment_t old_fs;
102
103 safe_store_code(new_code1, ip, faulted);
104 if (unlikely(faulted))
105 return -EFAULT;
106
107 ip += 4;
108 safe_store_code(new_code2, ip, faulted);
109 if (unlikely(faulted))
110 return -EFAULT;
111
112 ip -= 4;
113 old_fs = get_fs();
114 set_fs(get_ds());
115 flush_icache_range(ip, ip + 8);
116 set_fs(old_fs);
117
118 return 0;
119}
120
121static int ftrace_modify_code_2r(unsigned long ip, unsigned int new_code1,
122 unsigned int new_code2)
123{
124 int faulted;
125 mm_segment_t old_fs;
126
127 ip += 4;
128 safe_store_code(new_code2, ip, faulted);
129 if (unlikely(faulted))
130 return -EFAULT;
131
132 ip -= 4;
133 safe_store_code(new_code1, ip, faulted);
134 if (unlikely(faulted))
135 return -EFAULT;
136
137 old_fs = get_fs();
138 set_fs(get_ds());
139 flush_icache_range(ip, ip + 8);
140 set_fs(old_fs);
141
142 return 0;
143}
144#endif
145
146/*
147 * The details about the calling site of mcount on MIPS
148 *
149 * 1. For kernel:
150 *
151 * move at, ra
152 * jal _mcount --> nop
153 * sub sp, sp, 8 --> nop (CONFIG_32BIT)
154 *
155 * 2. For modules:
156 *
157 * 2.1 For KBUILD_MCOUNT_RA_ADDRESS and CONFIG_32BIT
158 *
159 * lui v1, hi_16bit_of_mcount --> b 1f (0x10000005)
160 * addiu v1, v1, low_16bit_of_mcount --> nop (CONFIG_32BIT)
161 * move at, ra
162 * move $12, ra_address
163 * jalr v1
164 * sub sp, sp, 8
165 * 1: offset = 5 instructions
166 * 2.2 For the Other situations
167 *
168 * lui v1, hi_16bit_of_mcount --> b 1f (0x10000004)
169 * addiu v1, v1, low_16bit_of_mcount --> nop (CONFIG_32BIT)
170 * move at, ra
171 * jalr v1
172 * nop | move $12, ra_address | sub sp, sp, 8
173 * 1: offset = 4 instructions
174 */
175
176#define INSN_B_1F (0x10000000 | MCOUNT_OFFSET_INSNS)
177
178int ftrace_make_nop(struct module *mod,
179 struct dyn_ftrace *rec, unsigned long addr)
180{
181 unsigned int new;
182 unsigned long ip = rec->ip;
183
184 /*
185 * If ip is in kernel space, no long call, otherwise, long call is
186 * needed.
187 */
188 new = core_kernel_text(ip) ? INSN_NOP : INSN_B_1F;
189#ifdef CONFIG_64BIT
190 return ftrace_modify_code(ip, new);
191#else
192 /*
193 * On 32 bit MIPS platforms, gcc adds a stack adjust
194 * instruction in the delay slot after the branch to
195 * mcount and expects mcount to restore the sp on return.
196 * This is based on a legacy API and does nothing but
197 * waste instructions so it's being removed at runtime.
198 */
199 return ftrace_modify_code_2(ip, new, INSN_NOP);
200#endif
201}
202
203int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
204{
205 unsigned int new;
206 unsigned long ip = rec->ip;
207
208 new = core_kernel_text(ip) ? insn_jal_ftrace_caller : insn_la_mcount[0];
209
210#ifdef CONFIG_64BIT
211 return ftrace_modify_code(ip, new);
212#else
213 return ftrace_modify_code_2r(ip, new, core_kernel_text(ip) ?
214 INSN_NOP : insn_la_mcount[1]);
215#endif
216}
217
218#define FTRACE_CALL_IP ((unsigned long)(&ftrace_call))
219
220int ftrace_update_ftrace_func(ftrace_func_t func)
221{
222 unsigned int new;
223
224 new = INSN_JAL((unsigned long)func);
225
226 return ftrace_modify_code(FTRACE_CALL_IP, new);
227}
228
229int __init ftrace_dyn_arch_init(void)
230{
231 /* Encode the instructions when booting */
232 ftrace_dyn_arch_init_insns();
233
234 /* Remove "b ftrace_stub" to ensure ftrace_caller() is executed */
235 ftrace_modify_code(MCOUNT_ADDR, INSN_NOP);
236
237 return 0;
238}
239#endif /* CONFIG_DYNAMIC_FTRACE */
240
241#ifdef CONFIG_FUNCTION_GRAPH_TRACER
242
243#ifdef CONFIG_DYNAMIC_FTRACE
244
245extern void ftrace_graph_call(void);
246#define FTRACE_GRAPH_CALL_IP ((unsigned long)(&ftrace_graph_call))
247
248int ftrace_enable_ftrace_graph_caller(void)
249{
250 return ftrace_modify_code(FTRACE_GRAPH_CALL_IP,
251 insn_j_ftrace_graph_caller);
252}
253
254int ftrace_disable_ftrace_graph_caller(void)
255{
256 return ftrace_modify_code(FTRACE_GRAPH_CALL_IP, INSN_NOP);
257}
258
259#endif /* CONFIG_DYNAMIC_FTRACE */
260
261#ifndef KBUILD_MCOUNT_RA_ADDRESS
262
263#define S_RA_SP (0xafbf << 16) /* s{d,w} ra, offset(sp) */
264#define S_R_SP (0xafb0 << 16) /* s{d,w} R, offset(sp) */
265#define OFFSET_MASK 0xffff /* stack offset range: 0 ~ PT_SIZE */
266
267unsigned long ftrace_get_parent_ra_addr(unsigned long self_ra, unsigned long
268 old_parent_ra, unsigned long parent_ra_addr, unsigned long fp)
269{
270 unsigned long sp, ip, tmp;
271 unsigned int code;
272 int faulted;
273
274 /*
275 * For module, move the ip from the return address after the
276 * instruction "lui v1, hi_16bit_of_mcount"(offset is 24), but for
277 * kernel, move after the instruction "move ra, at"(offset is 16)
278 */
279 ip = self_ra - (core_kernel_text(self_ra) ? 16 : 24);
280
281 /*
282 * search the text until finding the non-store instruction or "s{d,w}
283 * ra, offset(sp)" instruction
284 */
285 do {
286 /* get the code at "ip": code = *(unsigned int *)ip; */
287 safe_load_code(code, ip, faulted);
288
289 if (unlikely(faulted))
290 return 0;
291 /*
292 * If we hit the non-store instruction before finding where the
293 * ra is stored, then this is a leaf function and it does not
294 * store the ra on the stack
295 */
296 if ((code & S_R_SP) != S_R_SP)
297 return parent_ra_addr;
298
299 /* Move to the next instruction */
300 ip -= 4;
301 } while ((code & S_RA_SP) != S_RA_SP);
302
303 sp = fp + (code & OFFSET_MASK);
304
305 /* tmp = *(unsigned long *)sp; */
306 safe_load_stack(tmp, sp, faulted);
307 if (unlikely(faulted))
308 return 0;
309
310 if (tmp == old_parent_ra)
311 return sp;
312 return 0;
313}
314
315#endif /* !KBUILD_MCOUNT_RA_ADDRESS */
316
317/*
318 * Hook the return address and push it in the stack of return addrs
319 * in current thread info.
320 */
321void prepare_ftrace_return(unsigned long *parent_ra_addr, unsigned long self_ra,
322 unsigned long fp)
323{
324 unsigned long old_parent_ra;
325 struct ftrace_graph_ent trace;
326 unsigned long return_hooker = (unsigned long)
327 &return_to_handler;
328 int faulted, insns;
329
330 if (unlikely(ftrace_graph_is_dead()))
331 return;
332
333 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
334 return;
335
336 /*
337 * "parent_ra_addr" is the stack address saved the return address of
338 * the caller of _mcount.
339 *
340 * if the gcc < 4.5, a leaf function does not save the return address
341 * in the stack address, so, we "emulate" one in _mcount's stack space,
342 * and hijack it directly, but for a non-leaf function, it save the
343 * return address to the its own stack space, we can not hijack it
344 * directly, but need to find the real stack address,
345 * ftrace_get_parent_addr() does it!
346 *
347 * if gcc>= 4.5, with the new -mmcount-ra-address option, for a
348 * non-leaf function, the location of the return address will be saved
349 * to $12 for us, and for a leaf function, only put a zero into $12. we
350 * do it in ftrace_graph_caller of mcount.S.
351 */
352
353 /* old_parent_ra = *parent_ra_addr; */
354 safe_load_stack(old_parent_ra, parent_ra_addr, faulted);
355 if (unlikely(faulted))
356 goto out;
357#ifndef KBUILD_MCOUNT_RA_ADDRESS
358 parent_ra_addr = (unsigned long *)ftrace_get_parent_ra_addr(self_ra,
359 old_parent_ra, (unsigned long)parent_ra_addr, fp);
360 /*
361 * If fails when getting the stack address of the non-leaf function's
362 * ra, stop function graph tracer and return
363 */
364 if (parent_ra_addr == NULL)
365 goto out;
366#endif
367 /* *parent_ra_addr = return_hooker; */
368 safe_store_stack(return_hooker, parent_ra_addr, faulted);
369 if (unlikely(faulted))
370 goto out;
371
372 if (ftrace_push_return_trace(old_parent_ra, self_ra, &trace.depth, fp,
373 NULL) == -EBUSY) {
374 *parent_ra_addr = old_parent_ra;
375 return;
376 }
377
378 /*
379 * Get the recorded ip of the current mcount calling site in the
380 * __mcount_loc section, which will be used to filter the function
381 * entries configured through the tracing/set_graph_function interface.
382 */
383
384 insns = core_kernel_text(self_ra) ? 2 : MCOUNT_OFFSET_INSNS + 1;
385 trace.func = self_ra - (MCOUNT_INSN_SIZE * insns);
386
387 /* Only trace if the calling function expects to */
388 if (!ftrace_graph_entry(&trace)) {
389 current->curr_ret_stack--;
390 *parent_ra_addr = old_parent_ra;
391 }
392 return;
393out:
394 ftrace_graph_stop();
395 WARN_ON(1);
396}
397#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
398
399#ifdef CONFIG_FTRACE_SYSCALLS
400
401#ifdef CONFIG_32BIT
402unsigned long __init arch_syscall_addr(int nr)
403{
404 return (unsigned long)sys_call_table[nr - __NR_O32_Linux];
405}
406#endif
407
408#ifdef CONFIG_64BIT
409
410unsigned long __init arch_syscall_addr(int nr)
411{
412#ifdef CONFIG_MIPS32_N32
413 if (nr >= __NR_N32_Linux && nr <= __NR_N32_Linux + __NR_N32_Linux_syscalls)
414 return (unsigned long)sysn32_call_table[nr - __NR_N32_Linux];
415#endif
416 if (nr >= __NR_64_Linux && nr <= __NR_64_Linux + __NR_64_Linux_syscalls)
417 return (unsigned long)sys_call_table[nr - __NR_64_Linux];
418#ifdef CONFIG_MIPS32_O32
419 if (nr >= __NR_O32_Linux && nr <= __NR_O32_Linux + __NR_O32_Linux_syscalls)
420 return (unsigned long)sys32_call_table[nr - __NR_O32_Linux];
421#endif
422
423 return (unsigned long) &sys_ni_syscall;
424}
425#endif
426
427#endif /* CONFIG_FTRACE_SYSCALLS */
1/*
2 * Code for replacing ftrace calls with jumps.
3 *
4 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
5 * Copyright (C) 2009, 2010 DSLab, Lanzhou University, China
6 * Author: Wu Zhangjin <wuzhangjin@gmail.com>
7 *
8 * Thanks goes to Steven Rostedt for writing the original x86 version.
9 */
10
11#include <linux/uaccess.h>
12#include <linux/init.h>
13#include <linux/ftrace.h>
14
15#include <asm/asm.h>
16#include <asm/asm-offsets.h>
17#include <asm/cacheflush.h>
18#include <asm/uasm.h>
19
20#include <asm-generic/sections.h>
21
22#if defined(KBUILD_MCOUNT_RA_ADDRESS) && defined(CONFIG_32BIT)
23#define MCOUNT_OFFSET_INSNS 5
24#else
25#define MCOUNT_OFFSET_INSNS 4
26#endif
27
28/*
29 * Check if the address is in kernel space
30 *
31 * Clone core_kernel_text() from kernel/extable.c, but doesn't call
32 * init_kernel_text() for Ftrace doesn't trace functions in init sections.
33 */
34static inline int in_kernel_space(unsigned long ip)
35{
36 if (ip >= (unsigned long)_stext &&
37 ip <= (unsigned long)_etext)
38 return 1;
39 return 0;
40}
41
42#ifdef CONFIG_DYNAMIC_FTRACE
43
44#define JAL 0x0c000000 /* jump & link: ip --> ra, jump to target */
45#define ADDR_MASK 0x03ffffff /* op_code|addr : 31...26|25 ....0 */
46#define JUMP_RANGE_MASK ((1UL << 28) - 1)
47
48#define INSN_NOP 0x00000000 /* nop */
49#define INSN_JAL(addr) \
50 ((unsigned int)(JAL | (((addr) >> 2) & ADDR_MASK)))
51
52static unsigned int insn_jal_ftrace_caller __read_mostly;
53static unsigned int insn_lui_v1_hi16_mcount __read_mostly;
54static unsigned int insn_j_ftrace_graph_caller __maybe_unused __read_mostly;
55
56static inline void ftrace_dyn_arch_init_insns(void)
57{
58 u32 *buf;
59 unsigned int v1;
60
61 /* lui v1, hi16_mcount */
62 v1 = 3;
63 buf = (u32 *)&insn_lui_v1_hi16_mcount;
64 UASM_i_LA_mostly(&buf, v1, MCOUNT_ADDR);
65
66 /* jal (ftrace_caller + 8), jump over the first two instruction */
67 buf = (u32 *)&insn_jal_ftrace_caller;
68 uasm_i_jal(&buf, (FTRACE_ADDR + 8) & JUMP_RANGE_MASK);
69
70#ifdef CONFIG_FUNCTION_GRAPH_TRACER
71 /* j ftrace_graph_caller */
72 buf = (u32 *)&insn_j_ftrace_graph_caller;
73 uasm_i_j(&buf, (unsigned long)ftrace_graph_caller & JUMP_RANGE_MASK);
74#endif
75}
76
77static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
78{
79 int faulted;
80
81 /* *(unsigned int *)ip = new_code; */
82 safe_store_code(new_code, ip, faulted);
83
84 if (unlikely(faulted))
85 return -EFAULT;
86
87 flush_icache_range(ip, ip + 8);
88
89 return 0;
90}
91
92/*
93 * The details about the calling site of mcount on MIPS
94 *
95 * 1. For kernel:
96 *
97 * move at, ra
98 * jal _mcount --> nop
99 *
100 * 2. For modules:
101 *
102 * 2.1 For KBUILD_MCOUNT_RA_ADDRESS and CONFIG_32BIT
103 *
104 * lui v1, hi_16bit_of_mcount --> b 1f (0x10000005)
105 * addiu v1, v1, low_16bit_of_mcount
106 * move at, ra
107 * move $12, ra_address
108 * jalr v1
109 * sub sp, sp, 8
110 * 1: offset = 5 instructions
111 * 2.2 For the Other situations
112 *
113 * lui v1, hi_16bit_of_mcount --> b 1f (0x10000004)
114 * addiu v1, v1, low_16bit_of_mcount
115 * move at, ra
116 * jalr v1
117 * nop | move $12, ra_address | sub sp, sp, 8
118 * 1: offset = 4 instructions
119 */
120
121#define INSN_B_1F (0x10000000 | MCOUNT_OFFSET_INSNS)
122
123int ftrace_make_nop(struct module *mod,
124 struct dyn_ftrace *rec, unsigned long addr)
125{
126 unsigned int new;
127 unsigned long ip = rec->ip;
128
129 /*
130 * If ip is in kernel space, no long call, otherwise, long call is
131 * needed.
132 */
133 new = in_kernel_space(ip) ? INSN_NOP : INSN_B_1F;
134
135 return ftrace_modify_code(ip, new);
136}
137
138int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
139{
140 unsigned int new;
141 unsigned long ip = rec->ip;
142
143 new = in_kernel_space(ip) ? insn_jal_ftrace_caller :
144 insn_lui_v1_hi16_mcount;
145
146 return ftrace_modify_code(ip, new);
147}
148
149#define FTRACE_CALL_IP ((unsigned long)(&ftrace_call))
150
151int ftrace_update_ftrace_func(ftrace_func_t func)
152{
153 unsigned int new;
154
155 new = INSN_JAL((unsigned long)func);
156
157 return ftrace_modify_code(FTRACE_CALL_IP, new);
158}
159
160int __init ftrace_dyn_arch_init(void *data)
161{
162 /* Encode the instructions when booting */
163 ftrace_dyn_arch_init_insns();
164
165 /* Remove "b ftrace_stub" to ensure ftrace_caller() is executed */
166 ftrace_modify_code(MCOUNT_ADDR, INSN_NOP);
167
168 /* The return code is retured via data */
169 *(unsigned long *)data = 0;
170
171 return 0;
172}
173#endif /* CONFIG_DYNAMIC_FTRACE */
174
175#ifdef CONFIG_FUNCTION_GRAPH_TRACER
176
177#ifdef CONFIG_DYNAMIC_FTRACE
178
179extern void ftrace_graph_call(void);
180#define FTRACE_GRAPH_CALL_IP ((unsigned long)(&ftrace_graph_call))
181
182int ftrace_enable_ftrace_graph_caller(void)
183{
184 return ftrace_modify_code(FTRACE_GRAPH_CALL_IP,
185 insn_j_ftrace_graph_caller);
186}
187
188int ftrace_disable_ftrace_graph_caller(void)
189{
190 return ftrace_modify_code(FTRACE_GRAPH_CALL_IP, INSN_NOP);
191}
192
193#endif /* CONFIG_DYNAMIC_FTRACE */
194
195#ifndef KBUILD_MCOUNT_RA_ADDRESS
196
197#define S_RA_SP (0xafbf << 16) /* s{d,w} ra, offset(sp) */
198#define S_R_SP (0xafb0 << 16) /* s{d,w} R, offset(sp) */
199#define OFFSET_MASK 0xffff /* stack offset range: 0 ~ PT_SIZE */
200
201unsigned long ftrace_get_parent_ra_addr(unsigned long self_ra, unsigned long
202 old_parent_ra, unsigned long parent_ra_addr, unsigned long fp)
203{
204 unsigned long sp, ip, tmp;
205 unsigned int code;
206 int faulted;
207
208 /*
209 * For module, move the ip from the return address after the
210 * instruction "lui v1, hi_16bit_of_mcount"(offset is 24), but for
211 * kernel, move after the instruction "move ra, at"(offset is 16)
212 */
213 ip = self_ra - (in_kernel_space(self_ra) ? 16 : 24);
214
215 /*
216 * search the text until finding the non-store instruction or "s{d,w}
217 * ra, offset(sp)" instruction
218 */
219 do {
220 /* get the code at "ip": code = *(unsigned int *)ip; */
221 safe_load_code(code, ip, faulted);
222
223 if (unlikely(faulted))
224 return 0;
225 /*
226 * If we hit the non-store instruction before finding where the
227 * ra is stored, then this is a leaf function and it does not
228 * store the ra on the stack
229 */
230 if ((code & S_R_SP) != S_R_SP)
231 return parent_ra_addr;
232
233 /* Move to the next instruction */
234 ip -= 4;
235 } while ((code & S_RA_SP) != S_RA_SP);
236
237 sp = fp + (code & OFFSET_MASK);
238
239 /* tmp = *(unsigned long *)sp; */
240 safe_load_stack(tmp, sp, faulted);
241 if (unlikely(faulted))
242 return 0;
243
244 if (tmp == old_parent_ra)
245 return sp;
246 return 0;
247}
248
249#endif /* !KBUILD_MCOUNT_RA_ADDRESS */
250
251/*
252 * Hook the return address and push it in the stack of return addrs
253 * in current thread info.
254 */
255void prepare_ftrace_return(unsigned long *parent_ra_addr, unsigned long self_ra,
256 unsigned long fp)
257{
258 unsigned long old_parent_ra;
259 struct ftrace_graph_ent trace;
260 unsigned long return_hooker = (unsigned long)
261 &return_to_handler;
262 int faulted, insns;
263
264 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
265 return;
266
267 /*
268 * "parent_ra_addr" is the stack address saved the return address of
269 * the caller of _mcount.
270 *
271 * if the gcc < 4.5, a leaf function does not save the return address
272 * in the stack address, so, we "emulate" one in _mcount's stack space,
273 * and hijack it directly, but for a non-leaf function, it save the
274 * return address to the its own stack space, we can not hijack it
275 * directly, but need to find the real stack address,
276 * ftrace_get_parent_addr() does it!
277 *
278 * if gcc>= 4.5, with the new -mmcount-ra-address option, for a
279 * non-leaf function, the location of the return address will be saved
280 * to $12 for us, and for a leaf function, only put a zero into $12. we
281 * do it in ftrace_graph_caller of mcount.S.
282 */
283
284 /* old_parent_ra = *parent_ra_addr; */
285 safe_load_stack(old_parent_ra, parent_ra_addr, faulted);
286 if (unlikely(faulted))
287 goto out;
288#ifndef KBUILD_MCOUNT_RA_ADDRESS
289 parent_ra_addr = (unsigned long *)ftrace_get_parent_ra_addr(self_ra,
290 old_parent_ra, (unsigned long)parent_ra_addr, fp);
291 /*
292 * If fails when getting the stack address of the non-leaf function's
293 * ra, stop function graph tracer and return
294 */
295 if (parent_ra_addr == 0)
296 goto out;
297#endif
298 /* *parent_ra_addr = return_hooker; */
299 safe_store_stack(return_hooker, parent_ra_addr, faulted);
300 if (unlikely(faulted))
301 goto out;
302
303 if (ftrace_push_return_trace(old_parent_ra, self_ra, &trace.depth, fp)
304 == -EBUSY) {
305 *parent_ra_addr = old_parent_ra;
306 return;
307 }
308
309 /*
310 * Get the recorded ip of the current mcount calling site in the
311 * __mcount_loc section, which will be used to filter the function
312 * entries configured through the tracing/set_graph_function interface.
313 */
314
315 insns = in_kernel_space(self_ra) ? 2 : MCOUNT_OFFSET_INSNS + 1;
316 trace.func = self_ra - (MCOUNT_INSN_SIZE * insns);
317
318 /* Only trace if the calling function expects to */
319 if (!ftrace_graph_entry(&trace)) {
320 current->curr_ret_stack--;
321 *parent_ra_addr = old_parent_ra;
322 }
323 return;
324out:
325 ftrace_graph_stop();
326 WARN_ON(1);
327}
328#endif /* CONFIG_FUNCTION_GRAPH_TRACER */