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