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          * 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(&current->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 */