xref: /openbmc/linux/arch/arm64/kernel/ftrace.c (revision e8f6f3b4)
1 /*
2  * arch/arm64/kernel/ftrace.c
3  *
4  * Copyright (C) 2013 Linaro Limited
5  * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
6  *
7  * This program is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU General Public License version 2 as
9  * published by the Free Software Foundation.
10  */
11 
12 #include <linux/ftrace.h>
13 #include <linux/swab.h>
14 #include <linux/uaccess.h>
15 
16 #include <asm/cacheflush.h>
17 #include <asm/ftrace.h>
18 #include <asm/insn.h>
19 
20 #ifdef CONFIG_DYNAMIC_FTRACE
21 /*
22  * Replace a single instruction, which may be a branch or NOP.
23  * If @validate == true, a replaced instruction is checked against 'old'.
24  */
25 static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
26 			      bool validate)
27 {
28 	u32 replaced;
29 
30 	/*
31 	 * Note:
32 	 * Due to modules and __init, code can disappear and change,
33 	 * we need to protect against faulting as well as code changing.
34 	 * We do this by aarch64_insn_*() which use the probe_kernel_*().
35 	 *
36 	 * No lock is held here because all the modifications are run
37 	 * through stop_machine().
38 	 */
39 	if (validate) {
40 		if (aarch64_insn_read((void *)pc, &replaced))
41 			return -EFAULT;
42 
43 		if (replaced != old)
44 			return -EINVAL;
45 	}
46 	if (aarch64_insn_patch_text_nosync((void *)pc, new))
47 		return -EPERM;
48 
49 	return 0;
50 }
51 
52 /*
53  * Replace tracer function in ftrace_caller()
54  */
55 int ftrace_update_ftrace_func(ftrace_func_t func)
56 {
57 	unsigned long pc;
58 	u32 new;
59 
60 	pc = (unsigned long)&ftrace_call;
61 	new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
62 					  AARCH64_INSN_BRANCH_LINK);
63 
64 	return ftrace_modify_code(pc, 0, new, false);
65 }
66 
67 /*
68  * Turn on the call to ftrace_caller() in instrumented function
69  */
70 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
71 {
72 	unsigned long pc = rec->ip;
73 	u32 old, new;
74 
75 	old = aarch64_insn_gen_nop();
76 	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
77 
78 	return ftrace_modify_code(pc, old, new, true);
79 }
80 
81 /*
82  * Turn off the call to ftrace_caller() in instrumented function
83  */
84 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
85 		    unsigned long addr)
86 {
87 	unsigned long pc = rec->ip;
88 	u32 old, new;
89 
90 	old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
91 	new = aarch64_insn_gen_nop();
92 
93 	return ftrace_modify_code(pc, old, new, true);
94 }
95 
96 int __init ftrace_dyn_arch_init(void)
97 {
98 	return 0;
99 }
100 #endif /* CONFIG_DYNAMIC_FTRACE */
101 
102 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
103 /*
104  * function_graph tracer expects ftrace_return_to_handler() to be called
105  * on the way back to parent. For this purpose, this function is called
106  * in _mcount() or ftrace_caller() to replace return address (*parent) on
107  * the call stack to return_to_handler.
108  *
109  * Note that @frame_pointer is used only for sanity check later.
110  */
111 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
112 			   unsigned long frame_pointer)
113 {
114 	unsigned long return_hooker = (unsigned long)&return_to_handler;
115 	unsigned long old;
116 	struct ftrace_graph_ent trace;
117 	int err;
118 
119 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
120 		return;
121 
122 	/*
123 	 * Note:
124 	 * No protection against faulting at *parent, which may be seen
125 	 * on other archs. It's unlikely on AArch64.
126 	 */
127 	old = *parent;
128 	*parent = return_hooker;
129 
130 	trace.func = self_addr;
131 	trace.depth = current->curr_ret_stack + 1;
132 
133 	/* Only trace if the calling function expects to */
134 	if (!ftrace_graph_entry(&trace)) {
135 		*parent = old;
136 		return;
137 	}
138 
139 	err = ftrace_push_return_trace(old, self_addr, &trace.depth,
140 				       frame_pointer);
141 	if (err == -EBUSY) {
142 		*parent = old;
143 		return;
144 	}
145 }
146 
147 #ifdef CONFIG_DYNAMIC_FTRACE
148 /*
149  * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
150  * depending on @enable.
151  */
152 static int ftrace_modify_graph_caller(bool enable)
153 {
154 	unsigned long pc = (unsigned long)&ftrace_graph_call;
155 	u32 branch, nop;
156 
157 	branch = aarch64_insn_gen_branch_imm(pc,
158 					     (unsigned long)ftrace_graph_caller,
159 					     AARCH64_INSN_BRANCH_LINK);
160 	nop = aarch64_insn_gen_nop();
161 
162 	if (enable)
163 		return ftrace_modify_code(pc, nop, branch, true);
164 	else
165 		return ftrace_modify_code(pc, branch, nop, true);
166 }
167 
168 int ftrace_enable_ftrace_graph_caller(void)
169 {
170 	return ftrace_modify_graph_caller(true);
171 }
172 
173 int ftrace_disable_ftrace_graph_caller(void)
174 {
175 	return ftrace_modify_graph_caller(false);
176 }
177 #endif /* CONFIG_DYNAMIC_FTRACE */
178 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
179