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   1 /*
   2  * Dynamic function tracer architecture backend.
   3  *
   4  * Copyright IBM Corp. 2009
   5  *
   6  *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
   7  *
   8  */
   9
  10 #include <linux/uaccess.h>
  11 #include <linux/ftrace.h>
  12 #include <linux/kernel.h>
  13 #include <linux/types.h>
  14 #include <asm/lowcore.h>
  15
  16 void ftrace_disable_code(void);
  17 void ftrace_call_code(void);
  18 void ftrace_nop_code(void);
  19
  20 #define FTRACE_INSN_SIZE 4
  21
  22 #ifdef CONFIG_64BIT
  23
  24 asm(
  25         "       .align  4\n"
  26         "ftrace_disable_code:\n"
  27         "       j       0f\n"
  28         "       .word   0x0024\n"
  29         "       lg      %r1,"__stringify(__LC_FTRACE_FUNC)"\n"
  30         "       basr    %r14,%r1\n"
  31         "       lg      %r14,8(15)\n"
  32         "       lgr     %r0,%r0\n"
  33         "0:\n");
  34
  35 asm(
  36         "       .align  4\n"
  37         "ftrace_nop_code:\n"
  38         "       j       .+"__stringify(MCOUNT_INSN_SIZE)"\n");
  39
  40 asm(
  41         "       .align  4\n"
  42         "ftrace_call_code:\n"
  43         "       stg     %r14,8(%r15)\n");
  44
  45 #else /* CONFIG_64BIT */
  46
  47 asm(
  48         "       .align  4\n"
  49         "ftrace_disable_code:\n"
  50         "       j       0f\n"
  51         "       l       %r1,"__stringify(__LC_FTRACE_FUNC)"\n"
  52         "       basr    %r14,%r1\n"
  53         "       l       %r14,4(%r15)\n"
  54         "       j       0f\n"
  55         "       bcr     0,%r7\n"
  56         "       bcr     0,%r7\n"
  57         "       bcr     0,%r7\n"
  58         "       bcr     0,%r7\n"
  59         "       bcr     0,%r7\n"
  60         "       bcr     0,%r7\n"
  61         "0:\n");
  62
  63 asm(
  64         "       .align  4\n"
  65         "ftrace_nop_code:\n"
  66         "       j       .+"__stringify(MCOUNT_INSN_SIZE)"\n");
  67
  68 asm(
  69         "       .align  4\n"
  70         "ftrace_call_code:\n"
  71         "       st      %r14,4(%r15)\n");
  72
  73 #endif /* CONFIG_64BIT */
  74
  75 static int ftrace_modify_code(unsigned long ip,
  76                               void *old_code, int old_size,
  77                               void *new_code, int new_size)
  78 {
  79         unsigned char replaced[MCOUNT_INSN_SIZE];
  80
  81         /*
  82          * Note: Due to modules code can disappear and change.
  83          *  We need to protect against faulting as well as code
  84          *  changing. We do this by using the probe_kernel_*
  85          *  functions.
  86          *  This however is just a simple sanity check.
  87          */
  88         if (probe_kernel_read(replaced, (void *)ip, old_size))
  89                 return -EFAULT;
  90         if (memcmp(replaced, old_code, old_size) != 0)
  91                 return -EINVAL;
  92         if (probe_kernel_write((void *)ip, new_code, new_size))
  93                 return -EPERM;
  94         return 0;
  95 }
  96
  97 static int ftrace_make_initial_nop(struct module *mod, struct dyn_ftrace *rec,
  98                                    unsigned long addr)
  99 {
 100         return ftrace_modify_code(rec->ip,
 101                                   ftrace_call_code, FTRACE_INSN_SIZE,
 102                                   ftrace_disable_code, MCOUNT_INSN_SIZE);
 103 }
 104
 105 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 106                     unsigned long addr)
 107 {
 108         if (addr == MCOUNT_ADDR)
 109                 return ftrace_make_initial_nop(mod, rec, addr);
 110         return ftrace_modify_code(rec->ip,
 111                                   ftrace_call_code, FTRACE_INSN_SIZE,
 112                                   ftrace_nop_code, FTRACE_INSN_SIZE);
 113 }
 114
 115 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 116 {
 117         return ftrace_modify_code(rec->ip,
 118                                   ftrace_nop_code, FTRACE_INSN_SIZE,
 119                                   ftrace_call_code, FTRACE_INSN_SIZE);
 120 }
 121
 122 int ftrace_update_ftrace_func(ftrace_func_t func)
 123 {
 124         ftrace_dyn_func = (unsigned long)func;
 125         return 0;
 126 }
 127
 128 int __init ftrace_dyn_arch_init(void *data)
 129 {
 130         *(unsigned long *)data = 0;
 131         return 0;
 132 }