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(¤t->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_NOLINK); 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