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
  19 #ifdef CONFIG_64BIT
  20 #define MCOUNT_OFFSET_RET 12
  21 #else
  22 #define MCOUNT_OFFSET_RET 22
  23 #endif
  24
  25 #ifdef CONFIG_DYNAMIC_FTRACE
  26
  27 void ftrace_disable_code(void);
  28 void ftrace_enable_insn(void);
  29
  30 #ifdef CONFIG_64BIT
  31 /*
  32  * The 64-bit mcount code looks like this:
  33  *      stg     %r14,8(%r15)            # offset 0
  34  * >    larl    %r1,<&counter>          # offset 6
  35  * >    brasl   %r14,_mcount            # offset 12
  36  *      lg      %r14,8(%r15)            # offset 18
  37  * Total length is 24 bytes. The middle two instructions of the mcount
  38  * block get overwritten by ftrace_make_nop / ftrace_make_call.
  39  * The 64-bit enabled ftrace code block looks like this:
  40  *      stg     %r14,8(%r15)            # offset 0
  41  * >    lg      %r1,__LC_FTRACE_FUNC    # offset 6
  42  * >    lgr     %r0,%r0                 # offset 12
  43  * >    basr    %r14,%r1                # offset 16
  44  *      lg      %r14,8(%15)             # offset 18
  45  * The return points of the mcount/ftrace function have the same offset 18.
  46  * The 64-bit disable ftrace code block looks like this:
  47  *      stg     %r14,8(%r15)            # offset 0
  48  * >    jg      .+18                    # offset 6
  49  * >    lgr     %r0,%r0                 # offset 12
  50  * >    basr    %r14,%r1                # offset 16
  51  *      lg      %r14,8(%15)             # offset 18
  52  * The jg instruction branches to offset 24 to skip as many instructions
  53  * as possible.
  54  */
  55 asm(
  56         "       .align  4\n"
  57         "ftrace_disable_code:\n"
  58         "       jg      0f\n"
  59         "       lgr     %r0,%r0\n"
  60         "       basr    %r14,%r1\n"
  61         "0:\n"
  62         "       .align  4\n"
  63         "ftrace_enable_insn:\n"
  64         "       lg      %r1,"__stringify(__LC_FTRACE_FUNC)"\n");
  65
  66 #define FTRACE_INSN_SIZE        6
  67
  68 #else /* CONFIG_64BIT */
  69 /*
  70  * The 31-bit mcount code looks like this:
  71  *      st      %r14,4(%r15)            # offset 0
  72  * >    bras    %r1,0f                  # offset 4
  73  * >    .long   _mcount                 # offset 8
  74  * >    .long   <&counter>              # offset 12
  75  * > 0: l       %r14,0(%r1)             # offset 16
  76  * >    l       %r1,4(%r1)              # offset 20
  77  *      basr    %r14,%r14               # offset 24
  78  *      l       %r14,4(%r15)            # offset 26
  79  * Total length is 30 bytes. The twenty bytes starting from offset 4
  80  * to offset 24 get overwritten by ftrace_make_nop / ftrace_make_call.
  81  * The 31-bit enabled ftrace code block looks like this:
  82  *      st      %r14,4(%r15)            # offset 0
  83  * >    l       %r14,__LC_FTRACE_FUNC   # offset 4
  84  * >    j       0f                      # offset 8
  85  * >    .fill   12,1,0x07               # offset 12
  86  *   0: basr    %r14,%r14               # offset 24
  87  *      l       %r14,4(%r14)            # offset 26
  88  * The return points of the mcount/ftrace function have the same offset 26.
  89  * The 31-bit disabled ftrace code block looks like this:
  90  *      st      %r14,4(%r15)            # offset 0
  91  * >    j       .+26                    # offset 4
  92  * >    j       0f                      # offset 8
  93  * >    .fill   12,1,0x07               # offset 12
  94  *   0: basr    %r14,%r14               # offset 24
  95  *      l       %r14,4(%r14)            # offset 26
  96  * The j instruction branches to offset 30 to skip as many instructions
  97  * as possible.
  98  */
  99 asm(
 100         "       .align  4\n"
 101         "ftrace_disable_code:\n"
 102         "       j       1f\n"
 103         "       j       0f\n"
 104         "       .fill   12,1,0x07\n"
 105         "0:     basr    %r14,%r14\n"
 106         "1:\n"
 107         "       .align  4\n"
 108         "ftrace_enable_insn:\n"
 109         "       l       %r14,"__stringify(__LC_FTRACE_FUNC)"\n");
 110
 111 #define FTRACE_INSN_SIZE        4
 112
 113 #endif /* CONFIG_64BIT */
 114
 115
 116 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 117                     unsigned long addr)
 118 {
 119         if (probe_kernel_write((void *) rec->ip, ftrace_disable_code,
 120                                MCOUNT_INSN_SIZE))
 121                 return -EPERM;
 122         return 0;
 123 }
 124
 125 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 126 {
 127         if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn,
 128                                FTRACE_INSN_SIZE))
 129                 return -EPERM;
 130         return 0;
 131 }
 132
 133 int ftrace_update_ftrace_func(ftrace_func_t func)
 134 {
 135         return 0;
 136 }
 137
 138 int __init ftrace_dyn_arch_init(void *data)
 139 {
 140         *(unsigned long *) data = 0;
 141         return 0;
 142 }
 143
 144 #endif /* CONFIG_DYNAMIC_FTRACE */
 145
 146 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 147 /*
 148  * Hook the return address and push it in the stack of return addresses
 149  * in current thread info.
 150  */
 151 unsigned long __kprobes prepare_ftrace_return(unsigned long parent,
 152                                               unsigned long ip)
 153 {
 154         struct ftrace_graph_ent trace;
 155
 156         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 157                 goto out;
 158         if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
 159                 goto out;
 160         trace.func = (ip & PSW_ADDR_INSN) - MCOUNT_OFFSET_RET;
 161         /* Only trace if the calling function expects to. */
 162         if (!ftrace_graph_entry(&trace)) {
 163                 current->curr_ret_stack--;
 164                 goto out;
 165         }
 166         parent = (unsigned long) return_to_handler;
 167 out:
 168         return parent;
 169 }
 170
 171 #ifdef CONFIG_DYNAMIC_FTRACE
 172 /*
 173  * Patch the kernel code at ftrace_graph_caller location. The instruction
 174  * there is branch relative and save to prepare_ftrace_return. To disable
 175  * the call to prepare_ftrace_return we patch the bras offset to point
 176  * directly after the instructions. To enable the call we calculate
 177  * the original offset to prepare_ftrace_return and put it back.
 178  */
 179 int ftrace_enable_ftrace_graph_caller(void)
 180 {
 181         unsigned short offset;
 182
 183         offset = ((void *) prepare_ftrace_return -
 184                   (void *) ftrace_graph_caller) / 2;
 185         return probe_kernel_write(ftrace_graph_caller + 2,
 186                                   &offset, sizeof(offset));
 187 }
 188
 189 int ftrace_disable_ftrace_graph_caller(void)
 190 {
 191         static unsigned short offset = 0x0002;
 192
 193         return probe_kernel_write(ftrace_graph_caller + 2,
 194                                   &offset, sizeof(offset));
 195 }
 196
 197 #endif /* CONFIG_DYNAMIC_FTRACE */
 198 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */