xref: /openbmc/linux/arch/arm/kernel/ftrace.c (revision c819e2cf)
1 /*
2  * Dynamic function tracing support.
3  *
4  * Copyright (C) 2008 Abhishek Sagar <sagar.abhishek@gmail.com>
5  * Copyright (C) 2010 Rabin Vincent <rabin@rab.in>
6  *
7  * For licencing details, see COPYING.
8  *
9  * Defines low-level handling of mcount calls when the kernel
10  * is compiled with the -pg flag. When using dynamic ftrace, the
11  * mcount call-sites get patched with NOP till they are enabled.
12  * All code mutation routines here are called under stop_machine().
13  */
14 
15 #include <linux/ftrace.h>
16 #include <linux/uaccess.h>
17 #include <linux/module.h>
18 #include <linux/stop_machine.h>
19 
20 #include <asm/cacheflush.h>
21 #include <asm/opcodes.h>
22 #include <asm/ftrace.h>
23 
24 #include "insn.h"
25 
26 #ifdef CONFIG_THUMB2_KERNEL
27 #define	NOP		0xf85deb04	/* pop.w {lr} */
28 #else
29 #define	NOP		0xe8bd4000	/* pop {lr} */
30 #endif
31 
32 #ifdef CONFIG_DYNAMIC_FTRACE
33 #ifdef CONFIG_OLD_MCOUNT
34 #define OLD_MCOUNT_ADDR	((unsigned long) mcount)
35 #define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
36 
37 #define	OLD_NOP		0xe1a00000	/* mov r0, r0 */
38 
39 static int __ftrace_modify_code(void *data)
40 {
41 	int *command = data;
42 
43 	set_kernel_text_rw();
44 	ftrace_modify_all_code(*command);
45 	set_kernel_text_ro();
46 
47 	return 0;
48 }
49 
50 void arch_ftrace_update_code(int command)
51 {
52 	stop_machine(__ftrace_modify_code, &command, NULL);
53 }
54 
55 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
56 {
57 	return rec->arch.old_mcount ? OLD_NOP : NOP;
58 }
59 
60 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
61 {
62 	if (!rec->arch.old_mcount)
63 		return addr;
64 
65 	if (addr == MCOUNT_ADDR)
66 		addr = OLD_MCOUNT_ADDR;
67 	else if (addr == FTRACE_ADDR)
68 		addr = OLD_FTRACE_ADDR;
69 
70 	return addr;
71 }
72 #else
73 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
74 {
75 	return NOP;
76 }
77 
78 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
79 {
80 	return addr;
81 }
82 #endif
83 
84 int ftrace_arch_code_modify_prepare(void)
85 {
86 	set_all_modules_text_rw();
87 	return 0;
88 }
89 
90 int ftrace_arch_code_modify_post_process(void)
91 {
92 	set_all_modules_text_ro();
93 	/* Make sure any TLB misses during machine stop are cleared. */
94 	flush_tlb_all();
95 	return 0;
96 }
97 
98 static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
99 {
100 	return arm_gen_branch_link(pc, addr);
101 }
102 
103 static int ftrace_modify_code(unsigned long pc, unsigned long old,
104 			      unsigned long new, bool validate)
105 {
106 	unsigned long replaced;
107 
108 	if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
109 		old = __opcode_to_mem_thumb32(old);
110 		new = __opcode_to_mem_thumb32(new);
111 	} else {
112 		old = __opcode_to_mem_arm(old);
113 		new = __opcode_to_mem_arm(new);
114 	}
115 
116 	if (validate) {
117 		if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
118 			return -EFAULT;
119 
120 		if (replaced != old)
121 			return -EINVAL;
122 	}
123 
124 	if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
125 		return -EPERM;
126 
127 	flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
128 
129 	return 0;
130 }
131 
132 int ftrace_update_ftrace_func(ftrace_func_t func)
133 {
134 	unsigned long pc;
135 	unsigned long new;
136 	int ret;
137 
138 	pc = (unsigned long)&ftrace_call;
139 	new = ftrace_call_replace(pc, (unsigned long)func);
140 
141 	ret = ftrace_modify_code(pc, 0, new, false);
142 
143 #ifdef CONFIG_OLD_MCOUNT
144 	if (!ret) {
145 		pc = (unsigned long)&ftrace_call_old;
146 		new = ftrace_call_replace(pc, (unsigned long)func);
147 
148 		ret = ftrace_modify_code(pc, 0, new, false);
149 	}
150 #endif
151 
152 	return ret;
153 }
154 
155 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
156 {
157 	unsigned long new, old;
158 	unsigned long ip = rec->ip;
159 
160 	old = ftrace_nop_replace(rec);
161 	new = ftrace_call_replace(ip, adjust_address(rec, addr));
162 
163 	return ftrace_modify_code(rec->ip, old, new, true);
164 }
165 
166 int ftrace_make_nop(struct module *mod,
167 		    struct dyn_ftrace *rec, unsigned long addr)
168 {
169 	unsigned long ip = rec->ip;
170 	unsigned long old;
171 	unsigned long new;
172 	int ret;
173 
174 	old = ftrace_call_replace(ip, adjust_address(rec, addr));
175 	new = ftrace_nop_replace(rec);
176 	ret = ftrace_modify_code(ip, old, new, true);
177 
178 #ifdef CONFIG_OLD_MCOUNT
179 	if (ret == -EINVAL && addr == MCOUNT_ADDR) {
180 		rec->arch.old_mcount = true;
181 
182 		old = ftrace_call_replace(ip, adjust_address(rec, addr));
183 		new = ftrace_nop_replace(rec);
184 		ret = ftrace_modify_code(ip, old, new, true);
185 	}
186 #endif
187 
188 	return ret;
189 }
190 
191 int __init ftrace_dyn_arch_init(void)
192 {
193 	return 0;
194 }
195 #endif /* CONFIG_DYNAMIC_FTRACE */
196 
197 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
198 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
199 			   unsigned long frame_pointer)
200 {
201 	unsigned long return_hooker = (unsigned long) &return_to_handler;
202 	struct ftrace_graph_ent trace;
203 	unsigned long old;
204 	int err;
205 
206 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
207 		return;
208 
209 	old = *parent;
210 	*parent = return_hooker;
211 
212 	trace.func = self_addr;
213 	trace.depth = current->curr_ret_stack + 1;
214 
215 	/* Only trace if the calling function expects to */
216 	if (!ftrace_graph_entry(&trace)) {
217 		*parent = old;
218 		return;
219 	}
220 
221 	err = ftrace_push_return_trace(old, self_addr, &trace.depth,
222 				       frame_pointer);
223 	if (err == -EBUSY) {
224 		*parent = old;
225 		return;
226 	}
227 }
228 
229 #ifdef CONFIG_DYNAMIC_FTRACE
230 extern unsigned long ftrace_graph_call;
231 extern unsigned long ftrace_graph_call_old;
232 extern void ftrace_graph_caller_old(void);
233 
234 static int __ftrace_modify_caller(unsigned long *callsite,
235 				  void (*func) (void), bool enable)
236 {
237 	unsigned long caller_fn = (unsigned long) func;
238 	unsigned long pc = (unsigned long) callsite;
239 	unsigned long branch = arm_gen_branch(pc, caller_fn);
240 	unsigned long nop = 0xe1a00000;	/* mov r0, r0 */
241 	unsigned long old = enable ? nop : branch;
242 	unsigned long new = enable ? branch : nop;
243 
244 	return ftrace_modify_code(pc, old, new, true);
245 }
246 
247 static int ftrace_modify_graph_caller(bool enable)
248 {
249 	int ret;
250 
251 	ret = __ftrace_modify_caller(&ftrace_graph_call,
252 				     ftrace_graph_caller,
253 				     enable);
254 
255 #ifdef CONFIG_OLD_MCOUNT
256 	if (!ret)
257 		ret = __ftrace_modify_caller(&ftrace_graph_call_old,
258 					     ftrace_graph_caller_old,
259 					     enable);
260 #endif
261 
262 	return ret;
263 }
264 
265 int ftrace_enable_ftrace_graph_caller(void)
266 {
267 	return ftrace_modify_graph_caller(true);
268 }
269 
270 int ftrace_disable_ftrace_graph_caller(void)
271 {
272 	return ftrace_modify_graph_caller(false);
273 }
274 #endif /* CONFIG_DYNAMIC_FTRACE */
275 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
276