arch/arm64/kernel/ftrace.c

   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(&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, NULL);
 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 */