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 /* Syminfo callback.  */
 147
 148 void
 149 __go_syminfo_fnname_callback (void *data,
 150                               uintptr_t pc __attribute__ ((unused)),
 151                               const char *symname,
 152                               uintptr_t address __attribute__ ((unused)),
 153                               uintptr_t size __attribute__ ((unused)))
 154 {
 155   String* strptr = (String*) data;
 156
 157   if (symname != NULL)
 158     *strptr = runtime_gostringnocopy ((const byte *) symname);
 159 }
 160
 161 /* Error callback.  */
 162
 163 static void
 164 error_callback (void *data __attribute__ ((unused)),
 165                 const char *msg, int errnum)
 166 {
 167   if (errnum == -1)
 168     {
 169       /* No debug info available.  Carry on as best we can.  */
 170       return;
 171     }
 172   if (errnum != 0)
 173     runtime_printf ("%s errno %d\n", msg, errnum);
 174   runtime_throw (msg);
 175 }
 176
 177 /* Return whether we are already collecting a stack trace. This is
 178    called from the signal handler.  */
 179
 180 bool alreadyInCallers(void)
 181   __attribute__ ((no_split_stack));
 182 bool alreadyInCallers(void)
 183   __asm__ (GOSYM_PREFIX "runtime.alreadyInCallers");
 184
 185 bool
 186 alreadyInCallers()
 187 {
 188   return runtime_atomicload(&runtime_in_callers) > 0;
 189 }
 190
 191 /* Gather caller PC's.  */
 192
 193 int32
 194 runtime_callers (int32 skip, Location *locbuf, int32 m, bool keep_thunks)
 195 {
 196   struct callers_data data;
 197   struct backtrace_state* state;
 198   int32 i;
 199
 200   data.locbuf = locbuf;
 201   data.skip = skip + 1;
 202   data.index = 0;
 203   data.max = m;
 204   data.keep_thunks = keep_thunks;
 205   state = __go_get_backtrace_state ();
 206   runtime_xadd (&runtime_in_callers, 1);
 207   backtrace_full (state, 0, callback, error_callback, &data);
 208   runtime_xadd (&runtime_in_callers, -1);
 209
 210   /* For some reason GCC sometimes loses the name of a thunk function
 211      at the top of the stack.  If we are skipping thunks, skip that
 212      one too.  */
 213   if (!keep_thunks
 214       && data.index > 2
 215       && locbuf[data.index - 2].function.len == 0
 216       && locbuf[data.index - 1].function.str != NULL
 217       && __builtin_strcmp ((const char *) locbuf[data.index - 1].function.str,
 218                            "runtime.kickoff") == 0)
 219     {
 220       locbuf[data.index - 2] = locbuf[data.index - 1];
 221       --data.index;
 222     }
 223
 224   /* Try to use backtrace_syminfo to fill in any missing function
 225      names.  This can happen when tracing through an object which has
 226      no debug info; backtrace_syminfo will look at the symbol table to
 227      get the name.  This should only happen when tracing through code
 228      that is not written in Go and is not part of libgo.  */
 229   for (i = 0; i < data.index; ++i)
 230     {
 231       if (locbuf[i].function.len == 0 && locbuf[i].pc != 0)
 232         backtrace_syminfo (state, locbuf[i].pc, __go_syminfo_fnname_callback,
 233                            error_callback, &locbuf[i].function);
 234     }
 235
 236   return data.index;
 237 }
 238
 239 int Callers (int, struct __go_open_array)
 240   __asm__ (GOSYM_PREFIX "runtime.Callers");
 241
 242 int
 243 Callers (int skip, struct __go_open_array pc)
 244 {
 245   Location *locbuf;
 246   int ret;
 247   int i;
 248
 249   /* Note that calling mallocgc here assumes that we are not going to
 250      store any allocated Go pointers in the slice.  */
 251   locbuf = (Location *) runtime_mallocgc (pc.__count * sizeof (Location),
 252                                           nil, false);
 253
 254   /* In the Go 1 release runtime.Callers has an off-by-one error,
 255      which we can not correct because it would break backward
 256      compatibility.  Normally we would add 1 to SKIP here, but we
 257      don't so that we are compatible.  */
 258   ret = runtime_callers (skip, locbuf, pc.__count, false);
 259
 260   for (i = 0; i < ret; i++)
 261     ((uintptr *) pc.__values)[i] = locbuf[i].pc;
 262
 263   return ret;
 264 }