arch/s390/kernel/ftrace.c

   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  *              Martin Schwidefsky <schwidefsky@de.ibm.com>
   8  */
   9
  10 #include <linux/hardirq.h>
  11 #include <linux/uaccess.h>
  12 #include <linux/ftrace.h>
  13 #include <linux/kernel.h>
  14 #include <linux/types.h>
  15 #include <linux/kprobes.h>
  16 #include <trace/syscall.h>
  17 #include <asm/asm-offsets.h>
  18 #include "entry.h"
  19
  20 #ifdef CONFIG_DYNAMIC_FTRACE
  21
  22 void ftrace_disable_code(void);
  23 void ftrace_enable_insn(void);
  24
  25 #ifdef CONFIG_64BIT
  26 /*
  27  * The 64-bit mcount code looks like this:
  28  *      stg     %r14,8(%r15)            # offset 0
  29  * >    larl    %r1,<&counter>          # offset 6
  30  * >    brasl   %r14,_mcount            # offset 12
  31  *      lg      %r14,8(%r15)            # offset 18
  32  * Total length is 24 bytes. The middle two instructions of the mcount
  33  * block get overwritten by ftrace_make_nop / ftrace_make_call.
  34  * The 64-bit enabled ftrace code block looks like this:
  35  *      stg     %r14,8(%r15)            # offset 0
  36  * >    lg      %r1,__LC_FTRACE_FUNC    # offset 6
  37  * >    lgr     %r0,%r0                 # offset 12
  38  * >    basr    %r14,%r1                # offset 16
  39  *      lg      %r14,8(%15)             # offset 18
  40  * The return points of the mcount/ftrace function have the same offset 18.
  41  * The 64-bit disable ftrace code block looks like this:
  42  *      stg     %r14,8(%r15)            # offset 0
  43  * >    jg      .+18                    # offset 6
  44  * >    lgr     %r0,%r0                 # offset 12
  45  * >    basr    %r14,%r1                # offset 16
  46  *      lg      %r14,8(%15)             # offset 18
  47  * The jg instruction branches to offset 24 to skip as many instructions
  48  * as possible.
  49  */
  50 asm(
  51         "       .align  4\n"
  52         "ftrace_disable_code:\n"
  53         "       jg      0f\n"
  54         "       lgr     %r0,%r0\n"
  55         "       basr    %r14,%r1\n"
  56         "0:\n"
  57         "       .align  4\n"
  58         "ftrace_enable_insn:\n"
  59         "       lg      %r1,"__stringify(__LC_FTRACE_FUNC)"\n");
  60
  61 #define FTRACE_INSN_SIZE        6
  62
  63 #else /* CONFIG_64BIT */
  64 /*
  65  * The 31-bit mcount code looks like this:
  66  *      st      %r14,4(%r15)            # offset 0
  67  * >    bras    %r1,0f                  # offset 4
  68  * >    .long   _mcount                 # offset 8
  69  * >    .long   <&counter>              # offset 12
  70  * > 0: l       %r14,0(%r1)             # offset 16
  71  * >    l       %r1,4(%r1)              # offset 20
  72  *      basr    %r14,%r14               # offset 24
  73  *      l       %r14,4(%r15)            # offset 26
  74  * Total length is 30 bytes. The twenty bytes starting from offset 4
  75  * to offset 24 get overwritten by ftrace_make_nop / ftrace_make_call.
  76  * The 31-bit enabled ftrace code block looks like this:
  77  *      st      %r14,4(%r15)            # offset 0
  78  * >    l       %r14,__LC_FTRACE_FUNC   # offset 4
  79  * >    j       0f                      # offset 8
  80  * >    .fill   12,1,0x07               # offset 12
  81  *   0: basr    %r14,%r14               # offset 24
  82  *      l       %r14,4(%r14)            # offset 26
  83  * The return points of the mcount/ftrace function have the same offset 26.
  84  * The 31-bit disabled ftrace code block looks like this:
  85  *      st      %r14,4(%r15)            # offset 0
  86  * >    j       .+26                    # offset 4
  87  * >    j       0f                      # offset 8
  88  * >    .fill   12,1,0x07               # offset 12
  89  *   0: basr    %r14,%r14               # offset 24
  90  *      l       %r14,4(%r14)            # offset 26
  91  * The j instruction branches to offset 30 to skip as many instructions
  92  * as possible.
  93  */
  94 asm(
  95         "       .align  4\n"
  96         "ftrace_disable_code:\n"
  97         "       j       1f\n"
  98         "       j       0f\n"
  99         "       .fill   12,1,0x07\n"
 100         "0:     basr    %r14,%r14\n"
 101         "1:\n"
 102         "       .align  4\n"
 103         "ftrace_enable_insn:\n"
 104         "       l       %r14,"__stringify(__LC_FTRACE_FUNC)"\n");
 105
 106 #define FTRACE_INSN_SIZE        4
 107
 108 #endif /* CONFIG_64BIT */
 109
 110
 111 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 112                     unsigned long addr)
 113 {
 114         if (probe_kernel_write((void *) rec->ip, ftrace_disable_code,
 115                                MCOUNT_INSN_SIZE))
 116                 return -EPERM;
 117         return 0;
 118 }
 119
 120 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 121 {
 122         if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn,
 123                                FTRACE_INSN_SIZE))
 124                 return -EPERM;
 125         return 0;
 126 }
 127
 128 int ftrace_update_ftrace_func(ftrace_func_t func)
 129 {
 130         return 0;
 131 }
 132
 133 int __init ftrace_dyn_arch_init(void *data)
 134 {
 135         *(unsigned long *) data = 0;
 136         return 0;
 137 }
 138
 139 #endif /* CONFIG_DYNAMIC_FTRACE */
 140
 141 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 142 /*
 143  * Hook the return address and push it in the stack of return addresses
 144  * in current thread info.
 145  */
 146 unsigned long __kprobes prepare_ftrace_return(unsigned long parent,
 147                                               unsigned long ip)
 148 {
 149         struct ftrace_graph_ent trace;
 150
 151         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 152                 goto out;
 153         ip = (ip & PSW_ADDR_INSN) - MCOUNT_INSN_SIZE;
 154         if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
 155                 goto out;
 156         trace.func = ip;
 157         /* Only trace if the calling function expects to. */
 158         if (!ftrace_graph_entry(&trace)) {
 159                 current->curr_ret_stack--;
 160                 goto out;
 161         }
 162         parent = (unsigned long) return_to_handler;
 163 out:
 164         return parent;
 165 }
 166
 167 #ifdef CONFIG_DYNAMIC_FTRACE
 168 /*
 169  * Patch the kernel code at ftrace_graph_caller location. The instruction
 170  * there is branch relative and save to prepare_ftrace_return. To disable
 171  * the call to prepare_ftrace_return we patch the bras offset to point
 172  * directly after the instructions. To enable the call we calculate
 173  * the original offset to prepare_ftrace_return and put it back.
 174  */
 175 int ftrace_enable_ftrace_graph_caller(void)
 176 {
 177         unsigned short offset;
 178
 179         offset = ((void *) prepare_ftrace_return -
 180                   (void *) ftrace_graph_caller) / 2;
 181         return probe_kernel_write((void *) ftrace_graph_caller + 2,
 182                                   &offset, sizeof(offset));
 183 }
 184
 185 int ftrace_disable_ftrace_graph_caller(void)
 186 {
 187         static unsigned short offset = 0x0002;
 188
 189         return probe_kernel_write((void *) ftrace_graph_caller + 2,
 190                                   &offset, sizeof(offset));
 191 }
 192
 193 #endif /* CONFIG_DYNAMIC_FTRACE */
 194 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */