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, true); 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, true); 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, true); 90 new = aarch64_insn_gen_nop(); 91 92 return ftrace_modify_code(pc, old, new, true); 93 } 94 95 int __init ftrace_dyn_arch_init(void) 96 { 97 return 0; 98 } 99 #endif /* CONFIG_DYNAMIC_FTRACE */ 100 101 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 102 /* 103 * function_graph tracer expects ftrace_return_to_handler() to be called 104 * on the way back to parent. For this purpose, this function is called 105 * in _mcount() or ftrace_caller() to replace return address (*parent) on 106 * the call stack to return_to_handler. 107 * 108 * Note that @frame_pointer is used only for sanity check later. 109 */ 110 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, 111 unsigned long frame_pointer) 112 { 113 unsigned long return_hooker = (unsigned long)&return_to_handler; 114 unsigned long old; 115 struct ftrace_graph_ent trace; 116 int err; 117 118 if (unlikely(atomic_read(¤t->tracing_graph_pause))) 119 return; 120 121 /* 122 * Note: 123 * No protection against faulting at *parent, which may be seen 124 * on other archs. It's unlikely on AArch64. 125 */ 126 old = *parent; 127 *parent = return_hooker; 128 129 trace.func = self_addr; 130 trace.depth = current->curr_ret_stack + 1; 131 132 /* Only trace if the calling function expects to */ 133 if (!ftrace_graph_entry(&trace)) { 134 *parent = old; 135 return; 136 } 137 138 err = ftrace_push_return_trace(old, self_addr, &trace.depth, 139 frame_pointer); 140 if (err == -EBUSY) { 141 *parent = old; 142 return; 143 } 144 } 145 146 #ifdef CONFIG_DYNAMIC_FTRACE 147 /* 148 * Turn on/off the call to ftrace_graph_caller() in ftrace_caller() 149 * depending on @enable. 150 */ 151 static int ftrace_modify_graph_caller(bool enable) 152 { 153 unsigned long pc = (unsigned long)&ftrace_graph_call; 154 u32 branch, nop; 155 156 branch = aarch64_insn_gen_branch_imm(pc, 157 (unsigned long)ftrace_graph_caller, false); 158 nop = aarch64_insn_gen_nop(); 159 160 if (enable) 161 return ftrace_modify_code(pc, nop, branch, true); 162 else 163 return ftrace_modify_code(pc, branch, nop, true); 164 } 165 166 int ftrace_enable_ftrace_graph_caller(void) 167 { 168 return ftrace_modify_graph_caller(true); 169 } 170 171 int ftrace_disable_ftrace_graph_caller(void) 172 { 173 return ftrace_modify_graph_caller(false); 174 } 175 #endif /* CONFIG_DYNAMIC_FTRACE */ 176 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 177