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 */
25static 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 */
55int 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 */
70int 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 */
84int 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
96int __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 */
111void 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 */
152static 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
168int ftrace_enable_ftrace_graph_caller(void)
169{
170	return ftrace_modify_graph_caller(true);
171}
172
173int 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