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 * 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 */ 54 int 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 */ 69 int 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 */ 83 int 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 95 void arch_ftrace_update_code(int command) 96 { 97 ftrace_modify_all_code(command); 98 } 99 100 int __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 */ 115 void 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(¤t->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 */ 153 static 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 } 168 169 int ftrace_enable_ftrace_graph_caller(void) 170 { 171 return ftrace_modify_graph_caller(true); 172 } 173 174 int 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 */ 180