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