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, 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(&current->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 */