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	 * We are paranoid about modifying text, as if a bug were to happen, it
 33	 * could cause us to read or write to someplace that could cause harm.
 34	 * Carefully read and modify the code with aarch64_insn_*() which uses
 35	 * probe_kernel_*(), and make sure what we read is what we expected it
 36	 * to be before modifying it.
 37	 */
 38	if (validate) {
 39		if (aarch64_insn_read((void *)pc, &replaced))
 40			return -EFAULT;
 41
 42		if (replaced != old)
 43			return -EINVAL;
 44	}
 45	if (aarch64_insn_patch_text_nosync((void *)pc, new))
 46		return -EPERM;
 47
 48	return 0;
 49}
 50
 51/*
 52 * Replace tracer function in ftrace_caller()
 53 */
 54int ftrace_update_ftrace_func(ftrace_func_t func)
 55{
 56	unsigned long pc;
 57	u32 new;
 58
 59	pc = (unsigned long)&ftrace_call;
 60	new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
 61					  AARCH64_INSN_BRANCH_LINK);
 62
 63	return ftrace_modify_code(pc, 0, new, false);
 64}
 65
 66/*
 67 * Turn on the call to ftrace_caller() in instrumented function
 68 */
 69int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 70{
 71	unsigned long pc = rec->ip;
 72	u32 old, new;
 73
 74	old = aarch64_insn_gen_nop();
 75	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
 76
 77	return ftrace_modify_code(pc, old, new, true);
 78}
 79
 80/*
 81 * Turn off the call to ftrace_caller() in instrumented function
 82 */
 83int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 84		    unsigned long addr)
 85{
 86	unsigned long pc = rec->ip;
 87	u32 old, new;
 88
 89	old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
 90	new = aarch64_insn_gen_nop();
 91
 92	return ftrace_modify_code(pc, old, new, true);
 93}
 94
 95void arch_ftrace_update_code(int command)
 96{
 97	ftrace_modify_all_code(command);
 98}
 99
100int __init ftrace_dyn_arch_init(void)
101{
102	return 0;
103}
104#endif /* CONFIG_DYNAMIC_FTRACE */
105
106#ifdef CONFIG_FUNCTION_GRAPH_TRACER
107/*
108 * function_graph tracer expects ftrace_return_to_handler() to be called
109 * on the way back to parent. For this purpose, this function is called
110 * in _mcount() or ftrace_caller() to replace return address (*parent) on
111 * the call stack to return_to_handler.
112 *
113 * Note that @frame_pointer is used only for sanity check later.
114 */
115void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
116			   unsigned long frame_pointer)
117{
118	unsigned long return_hooker = (unsigned long)&return_to_handler;
119	unsigned long old;
120	struct ftrace_graph_ent trace;
121	int err;
122
123	if (unlikely(atomic_read(&current->tracing_graph_pause)))
124		return;
125
126	/*
127	 * Note:
128	 * No protection against faulting at *parent, which may be seen
129	 * on other archs. It's unlikely on AArch64.
130	 */
131	old = *parent;
132
133	trace.func = self_addr;
134	trace.depth = current->curr_ret_stack + 1;
135
136	/* Only trace if the calling function expects to */
137	if (!ftrace_graph_entry(&trace))
138		return;
139
140	err = ftrace_push_return_trace(old, self_addr, &trace.depth,
141				       frame_pointer);
142	if (err == -EBUSY)
143		return;
144	else
145		*parent = return_hooker;
146}
147
148#ifdef CONFIG_DYNAMIC_FTRACE
149/*
150 * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
151 * depending on @enable.
152 */
153static int ftrace_modify_graph_caller(bool enable)
154{
155	unsigned long pc = (unsigned long)&ftrace_graph_call;
156	u32 branch, nop;
157
158	branch = aarch64_insn_gen_branch_imm(pc,
159					     (unsigned long)ftrace_graph_caller,
160					     AARCH64_INSN_BRANCH_NOLINK);
161	nop = aarch64_insn_gen_nop();
162
163	if (enable)
164		return ftrace_modify_code(pc, nop, branch, true);
165	else
166		return ftrace_modify_code(pc, branch, nop, true);
167}
168
169int ftrace_enable_ftrace_graph_caller(void)
170{
171	return ftrace_modify_graph_caller(true);
172}
173
174int ftrace_disable_ftrace_graph_caller(void)
175{
176	return ftrace_modify_graph_caller(false);
177}
178#endif /* CONFIG_DYNAMIC_FTRACE */
179#endif /* CONFIG_FUNCTION_GRAPH_TRACER */