libgo/runtime/go-callers.c

   1 /* go-callers.c -- get callers for Go.
   2
   3    Copyright 2012 The Go Authors. All rights reserved.
   4    Use of this source code is governed by a BSD-style
   5    license that can be found in the LICENSE file.  */
   6
   7 #include "config.h"
   8
   9 #include "backtrace.h"
  10
  11 #include "runtime.h"
  12 #include "array.h"
  13
  14 /* This is set to non-zero when calling backtrace_full.  This is used
  15    to avoid getting hanging on a recursive lock in dl_iterate_phdr on
  16    older versions of glibc when a SIGPROF signal arrives while
  17    collecting a backtrace.  */
  18
  19 static uint32 runtime_in_callers;
  20
  21 /* Argument passed to callback function.  */
  22
  23 struct callers_data
  24 {
  25   Location *locbuf;
  26   int skip;
  27   int index;
  28   int max;
  29   int keep_thunks;
  30 };
  31
  32 /* Callback function for backtrace_full.  Just collect the locations.
  33    Return zero to continue, non-zero to stop.  */
  34
  35 static int
  36 callback (void *data, uintptr_t pc, const char *filename, int lineno,
  37           const char *function)
  38 {
  39   struct callers_data *arg = (struct callers_data *) data;
  40   Location *loc;
  41
  42   /* Skip split stack functions.  */
  43   if (function != NULL)
  44     {
  45       const char *p;
  46
  47       p = function;
  48       if (__builtin_strncmp (p, "___", 3) == 0)
  49         ++p;
  50       if (__builtin_strncmp (p, "__morestack_", 12) == 0)
  51         return 0;
  52     }
  53   else if (filename != NULL)
  54     {
  55       const char *p;
  56
  57       p = strrchr (filename, '/');
  58       if (p == NULL)
  59         p = filename;
  60       if (__builtin_strncmp (p, "/morestack.S", 12) == 0)
  61         return 0;
  62     }
  63
  64   /* Skip thunks and recover functions.  There is no equivalent to
  65      these functions in the gc toolchain, so returning them here means
  66      significantly different results for runtime.Caller(N).  */
  67   if (function != NULL && !arg->keep_thunks)
  68     {
  69       const char *p;
  70
  71       p = function + __builtin_strlen (function);
  72       while (p > function && p[-1] >= '0' && p[-1] <= '9')
  73         --p;
  74       if (p - function > 7 && __builtin_strncmp (p - 7, "..thunk", 7) == 0)
  75         return 0;
  76       if (p - function > 3 && __builtin_strcmp (p - 3, "..r") == 0)
  77         return 0;
  78       if (p - function > 6 && __builtin_strcmp (p - 6, "..stub") == 0)
  79         return 0;
  80     }
  81
  82   if (arg->skip > 0)
  83     {
  84       --arg->skip;
  85       return 0;
  86     }
  87
  88   loc = &arg->locbuf[arg->index];
  89
  90   /* On the call to backtrace_full the pc value was most likely
  91      decremented if there was a normal call, since the pc referred to
  92      the instruction where the call returned and not the call itself.
  93      This was done so that the line number referred to the call
  94      instruction.  To make sure the actual pc from the call stack is
  95      used, it is incremented here.
  96
  97      In the case of a signal, the pc was not decremented by
  98      backtrace_full but still incremented here.  That doesn't really
  99      hurt anything since the line number is right and the pc refers to
 100      the same instruction.  */
 101
 102   loc->pc = pc + 1;
 103
 104   /* The libbacktrace library says that these strings might disappear,
 105      but with the current implementation they won't.  We can't easily
 106      allocate memory here, so for now assume that we can save a
 107      pointer to the strings.  */
 108   loc->filename = runtime_gostringnocopy ((const byte *) filename);
 109   loc->function = runtime_gostringnocopy ((const byte *) function);
 110
 111   loc->lineno = lineno;
 112   ++arg->index;
 113
 114   /* There is no point to tracing past certain runtime functions.
 115      Stopping the backtrace here can avoid problems on systems that
 116      don't provide proper unwind information for makecontext, such as
 117      Solaris (http://gcc.gnu.org/PR52583 comment #21).  */
 118   if (function != NULL)
 119     {
 120       if (__builtin_strcmp (function, "makecontext") == 0)
 121         return 1;
 122       if (filename != NULL)
 123         {
 124           const char *p;
 125
 126           p = strrchr (filename, '/');
 127           if (p == NULL)
 128             p = filename;
 129           if (__builtin_strcmp (p, "/proc.c") == 0)
 130             {
 131               if (__builtin_strcmp (function, "runtime_mstart") == 0)
 132                 return 1;
 133             }
 134           else if (__builtin_strcmp (p, "/proc.go") == 0)
 135             {
 136               if (__builtin_strcmp (function, "runtime.kickoff") == 0
 137                   || __builtin_strcmp (function, "runtime.main") == 0)
 138                 return 1;
 139             }
 140         }
 141     }
 142
 143   return arg->index >= arg->max;
 144 }
 145
 146 /* Error callback.  */
 147
 148 static void
 149 error_callback (void *data __attribute__ ((unused)),
 150                 const char *msg, int errnum)
 151 {
 152   if (errnum == -1)
 153     {
 154       /* No debug info available.  Carry on as best we can.  */
 155       return;
 156     }
 157   if (errnum != 0)
 158     runtime_printf ("%s errno %d\n", msg, errnum);
 159   runtime_throw (msg);
 160 }
 161
 162 /* Return whether we are already collecting a stack trace. This is
 163    called from the signal handler.  */
 164
 165 bool alreadyInCallers(void)
 166   __attribute__ ((no_split_stack));
 167 bool alreadyInCallers(void)
 168   __asm__ (GOSYM_PREFIX "runtime.alreadyInCallers");
 169
 170 bool
 171 alreadyInCallers()
 172 {
 173   return runtime_atomicload(&runtime_in_callers) > 0;
 174 }
 175
 176 /* Gather caller PC's.  */
 177
 178 int32
 179 runtime_callers (int32 skip, Location *locbuf, int32 m, bool keep_thunks)
 180 {
 181   struct callers_data data;
 182
 183   data.locbuf = locbuf;
 184   data.skip = skip + 1;
 185   data.index = 0;
 186   data.max = m;
 187   data.keep_thunks = keep_thunks;
 188   runtime_xadd (&runtime_in_callers, 1);
 189   backtrace_full (__go_get_backtrace_state (), 0, callback, error_callback,
 190                   &data);
 191   runtime_xadd (&runtime_in_callers, -1);
 192
 193   /* For some reason GCC sometimes loses the name of a thunk function
 194      at the top of the stack.  If we are skipping thunks, skip that
 195      one too.  */
 196   if (!keep_thunks
 197       && data.index > 2
 198       && locbuf[data.index - 2].function.len == 0
 199       && locbuf[data.index - 1].function.str != NULL
 200       && __builtin_strcmp ((const char *) locbuf[data.index - 1].function.str,
 201                            "runtime.kickoff") == 0)
 202     {
 203       locbuf[data.index - 2] = locbuf[data.index - 1];
 204       --data.index;
 205     }
 206
 207   return data.index;
 208 }
 209
 210 int Callers (int, struct __go_open_array)
 211   __asm__ (GOSYM_PREFIX "runtime.Callers");
 212
 213 int
 214 Callers (int skip, struct __go_open_array pc)
 215 {
 216   Location *locbuf;
 217   int ret;
 218   int i;
 219
 220   /* Note that calling mallocgc here assumes that we are not going to
 221      store any allocated Go pointers in the slice.  */
 222   locbuf = (Location *) runtime_mallocgc (pc.__count * sizeof (Location),
 223                                           nil, false);
 224
 225   /* In the Go 1 release runtime.Callers has an off-by-one error,
 226      which we can not correct because it would break backward
 227      compatibility.  Normally we would add 1 to SKIP here, but we
 228      don't so that we are compatible.  */
 229   ret = runtime_callers (skip, locbuf, pc.__count, false);
 230
 231   for (i = 0; i < ret; i++)
 232     ((uintptr *) pc.__values)[i] = locbuf[i].pc;
 233
 234   return ret;
 235 }