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 uint32 __go_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). See also
  67      similar code in runtime/mprof.go that strips out such functions
  68      for block/mutex/memory profiles.  */
  69   if (function != NULL && !arg->keep_thunks)
  70     {
  71       const char *p;
  72
  73       p = function + __builtin_strlen (function);
  74       while (p > function && p[-1] >= '0' && p[-1] <= '9')
  75         --p;
  76       if (p - function > 7 && __builtin_strncmp (p - 7, "..thunk", 7) == 0)
  77         return 0;
  78       if (p - function > 3 && __builtin_strcmp (p - 3, "..r") == 0)
  79         return 0;
  80       if (p - function > 6 && __builtin_strncmp (p - 6, "..stub", 6) == 0)
  81         return 0;
  82     }
  83
  84   if (arg->skip > 0)
  85     {
  86       --arg->skip;
  87       return 0;
  88     }
  89
  90   loc = &arg->locbuf[arg->index];
  91
  92   /* On the call to backtrace_full the pc value was most likely
  93      decremented if there was a normal call, since the pc referred to
  94      the instruction where the call returned and not the call itself.
  95      This was done so that the line number referred to the call
  96      instruction.  To make sure the actual pc from the call stack is
  97      used, it is incremented here.
  98
  99      In the case of a signal, the pc was not decremented by
 100      backtrace_full but still incremented here.  That doesn't really
 101      hurt anything since the line number is right and the pc refers to
 102      the same instruction.  */
 103
 104   loc->pc = pc + 1;
 105
 106   /* The libbacktrace library says that these strings might disappear,
 107      but with the current implementation they won't.  We can't easily
 108      allocate memory here, so for now assume that we can save a
 109      pointer to the strings.  */
 110   loc->filename = runtime_gostringnocopy ((const byte *) filename);
 111   loc->function = runtime_gostringnocopy ((const byte *) function);
 112
 113   loc->lineno = lineno;
 114   ++arg->index;
 115
 116   /* There is no point to tracing past certain runtime functions.
 117      Stopping the backtrace here can avoid problems on systems that
 118      don't provide proper unwind information for makecontext, such as
 119      Solaris (http://gcc.gnu.org/PR52583 comment #21).  */
 120   if (function != NULL)
 121     {
 122       if (__builtin_strcmp (function, "makecontext") == 0)
 123         return 1;
 124       if (filename != NULL)
 125         {
 126           const char *p;
 127
 128           p = strrchr (filename, '/');
 129           if (p == NULL)
 130             p = filename;
 131           if (__builtin_strcmp (p, "/proc.c") == 0)
 132             {
 133               if (__builtin_strcmp (function, "runtime_mstart") == 0)
 134                 return 1;
 135             }
 136           else if (__builtin_strcmp (p, "/proc.go") == 0)
 137             {
 138               if (__builtin_strcmp (function, "runtime.kickoff") == 0
 139                   || __builtin_strcmp (function, "runtime.main") == 0)
 140                 return 1;
 141             }
 142         }
 143     }
 144
 145   return arg->index >= arg->max;
 146 }
 147
 148 /* Syminfo callback.  */
 149
 150 void
 151 __go_syminfo_fnname_callback (void *data,
 152                               uintptr_t pc __attribute__ ((unused)),
 153                               const char *symname,
 154                               uintptr_t address __attribute__ ((unused)),
 155                               uintptr_t size __attribute__ ((unused)))
 156 {
 157   String* strptr = (String*) data;
 158
 159   if (symname != NULL)
 160     *strptr = runtime_gostringnocopy ((const byte *) symname);
 161 }
 162
 163 /* Error callback.  */
 164
 165 static void
 166 error_callback (void *data __attribute__ ((unused)),
 167                 const char *msg, int errnum)
 168 {
 169   if (errnum == -1)
 170     {
 171       /* No debug info available.  Carry on as best we can.  */
 172       return;
 173     }
 174   if (errnum != 0)
 175     runtime_printf ("%s errno %d\n", msg, errnum);
 176   runtime_throw (msg);
 177 }
 178
 179 /* Return whether we are already collecting a stack trace. This is
 180    called from the signal handler.  */
 181
 182 bool alreadyInCallers(void)
 183   __attribute__ ((no_split_stack));
 184 bool alreadyInCallers(void)
 185   __asm__ (GOSYM_PREFIX "runtime.alreadyInCallers");
 186
 187 bool
 188 alreadyInCallers()
 189 {
 190   return runtime_atomicload(&__go_runtime_in_callers) > 0;
 191 }
 192
 193 /* Gather caller PC's.  */
 194
 195 int32
 196 runtime_callers (int32 skip, Location *locbuf, int32 m, bool keep_thunks)
 197 {
 198   struct callers_data data;
 199   struct backtrace_state* state;
 200   int32 i;
 201
 202   data.locbuf = locbuf;
 203   data.skip = skip + 1;
 204   data.index = 0;
 205   data.max = m;
 206   data.keep_thunks = keep_thunks;
 207   runtime_xadd (&__go_runtime_in_callers, 1);
 208   state = __go_get_backtrace_state ();
 209   backtrace_full (state, 0, callback, error_callback, &data);
 210   runtime_xadd (&__go_runtime_in_callers, -1);
 211
 212   /* For some reason GCC sometimes loses the name of a thunk function
 213      at the top of the stack.  If we are skipping thunks, skip that
 214      one too.  */
 215   if (!keep_thunks
 216       && data.index > 2
 217       && locbuf[data.index - 2].function.len == 0
 218       && locbuf[data.index - 1].function.str != NULL
 219       && __builtin_strcmp ((const char *) locbuf[data.index - 1].function.str,
 220                            "runtime.kickoff") == 0)
 221     {
 222       locbuf[data.index - 2] = locbuf[data.index - 1];
 223       --data.index;
 224     }
 225
 226   /* Try to use backtrace_syminfo to fill in any missing function
 227      names.  This can happen when tracing through an object which has
 228      no debug info; backtrace_syminfo will look at the symbol table to
 229      get the name.  This should only happen when tracing through code
 230      that is not written in Go and is not part of libgo.  */
 231   for (i = 0; i < data.index; ++i)
 232     {
 233       if (locbuf[i].function.len == 0 && locbuf[i].pc != 0)
 234         backtrace_syminfo (state, locbuf[i].pc, __go_syminfo_fnname_callback,
 235                            error_callback, &locbuf[i].function);
 236     }
 237
 238   return data.index;
 239 }
 240
 241 intgo Callers (intgo, struct __go_open_array)
 242   __asm__ (GOSYM_PREFIX "runtime.Callers");
 243
 244 intgo
 245 Callers (intgo skip, struct __go_open_array pc)
 246 {
 247   Location *locbuf;
 248   int ret;
 249   int i;
 250
 251   /* Note that calling mallocgc here assumes that we are not going to
 252      store any allocated Go pointers in the slice.  */
 253   locbuf = (Location *) runtime_mallocgc (pc.__count * sizeof (Location),
 254                                           nil, false);
 255
 256   /* In the Go 1 release runtime.Callers has an off-by-one error,
 257      which we can not correct because it would break backward
 258      compatibility.  Normally we would add 1 to SKIP here, but we
 259      don't so that we are compatible.  */
 260   ret = runtime_callers (skip, locbuf, pc.__count, false);
 261
 262   for (i = 0; i < ret; i++)
 263     ((uintptr *) pc.__values)[i] = locbuf[i].pc;
 264
 265   return ret;
 266 }
 267
 268 struct callersRaw_data
 269 {
 270   uintptr* pcbuf;
 271   int index;
 272   int max;
 273 };
 274
 275 // Callback function for backtrace_simple.  Just collect pc's.
 276 // Return zero to continue, non-zero to stop.
 277
 278 static int callback_raw (void *data, uintptr_t pc)
 279 {
 280   struct callersRaw_data *arg = (struct callersRaw_data *) data;
 281
 282   /* On the call to backtrace_simple the pc value was most likely
 283      decremented if there was a normal call, since the pc referred to
 284      the instruction where the call returned and not the call itself.
 285      This was done so that the line number referred to the call
 286      instruction.  To make sure the actual pc from the call stack is
 287      used, it is incremented here.
 288
 289      In the case of a signal, the pc was not decremented by
 290      backtrace_full but still incremented here.  That doesn't really
 291      hurt anything since the line number is right and the pc refers to
 292      the same instruction.  */
 293
 294   arg->pcbuf[arg->index] = pc + 1;
 295   arg->index++;
 296   return arg->index >= arg->max;
 297 }
 298
 299 /* runtime_callersRaw is similar to runtime_callers() above, but
 300    it returns raw PC values as opposed to file/func/line locations. */
 301 int32
 302 runtime_callersRaw (uintptr *pcbuf, int32 m)
 303 {
 304   struct callersRaw_data data;
 305   struct backtrace_state* state;
 306
 307   data.pcbuf = pcbuf;
 308   data.index = 0;
 309   data.max = m;
 310   runtime_xadd (&__go_runtime_in_callers, 1);
 311   state = __go_get_backtrace_state ();
 312   backtrace_simple (state, 0, callback_raw, error_callback, &data);
 313   runtime_xadd (&__go_runtime_in_callers, -1);
 314
 315   return data.index;
 316 }
 317