libgo/runtime/go-unwind.c

   1 /* go-unwind.c -- unwind the stack for panic/recover.
   2
   3    Copyright 2010 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 <stdlib.h>
  10 #include <unistd.h>
  11
  12 #include "unwind.h"
  13 #define NO_SIZE_OF_ENCODED_VALUE
  14 #include "unwind-pe.h"
  15
  16 #include "runtime.h"
  17 #include "go-alloc.h"
  18 #include "go-defer.h"
  19 #include "go-panic.h"
  20
  21 /* The code for a Go exception.  */
  22
  23 #ifdef __ARM_EABI_UNWINDER__
  24 static const _Unwind_Exception_Class __go_exception_class =
  25   { 'G', 'N', 'U', 'C', 'G', 'O', '\0', '\0' };
  26 #else
  27 static const _Unwind_Exception_Class __go_exception_class =
  28   ((((((((_Unwind_Exception_Class) 'G'
  29          << 8 | (_Unwind_Exception_Class) 'N')
  30         << 8 | (_Unwind_Exception_Class) 'U')
  31        << 8 | (_Unwind_Exception_Class) 'C')
  32       << 8 | (_Unwind_Exception_Class) 'G')
  33      << 8 | (_Unwind_Exception_Class) 'O')
  34     << 8 | (_Unwind_Exception_Class) '\0')
  35    << 8 | (_Unwind_Exception_Class) '\0');
  36 #endif
  37
  38
  39 /* This function is called by exception handlers used when unwinding
  40    the stack after a recovered panic.  The exception handler looks
  41    like this:
  42      __go_check_defer (frame);
  43      return;
  44    If we have not yet reached the frame we are looking for, we
  45    continue unwinding.  */
  46
  47 void
  48 __go_check_defer (_Bool *frame)
  49 {
  50   G *g;
  51   struct _Unwind_Exception *hdr;
  52
  53   g = runtime_g ();
  54
  55   if (g == NULL)
  56     {
  57       /* Some other language has thrown an exception.  We know there
  58          are no defer handlers, so there is nothing to do.  */
  59     }
  60   else if (g->is_foreign)
  61     {
  62       struct __go_panic_stack *n;
  63       _Bool was_recovered;
  64
  65       /* Some other language has thrown an exception.  We need to run
  66          the local defer handlers.  If they call recover, we stop
  67          unwinding the stack here.  */
  68
  69       n = ((struct __go_panic_stack *)
  70            __go_alloc (sizeof (struct __go_panic_stack)));
  71
  72       n->__arg.__type_descriptor = NULL;
  73       n->__arg.__object = NULL;
  74       n->__was_recovered = 0;
  75       n->__is_foreign = 1;
  76       n->__next = g->panic;
  77       g->panic = n;
  78
  79       while (1)
  80         {
  81           struct __go_defer_stack *d;
  82           void (*pfn) (void *);
  83
  84           d = g->defer;
  85           if (d == NULL || d->__frame != frame || d->__pfn == NULL)
  86             break;
  87
  88           pfn = d->__pfn;
  89           g->defer = d->__next;
  90
  91           (*pfn) (d->__arg);
  92
  93           if (runtime_m () != NULL)
  94             runtime_freedefer (d);
  95
  96           if (n->__was_recovered)
  97             {
  98               /* The recover function caught the panic thrown by some
  99                  other language.  */
 100               break;
 101             }
 102         }
 103
 104       was_recovered = n->__was_recovered;
 105       g->panic = n->__next;
 106       __go_free (n);
 107
 108       if (was_recovered)
 109         {
 110           /* Just return and continue executing Go code.  */
 111           *frame = 1;
 112           return;
 113         }
 114
 115       /* We are panicing through this function.  */
 116       *frame = 0;
 117     }
 118   else if (g->defer != NULL
 119            && g->defer->__pfn == NULL
 120            && g->defer->__frame == frame)
 121     {
 122       struct __go_defer_stack *d;
 123
 124       /* This is the defer function which called recover.  Simply
 125          return to stop the stack unwind, and let the Go code continue
 126          to execute.  */
 127       d = g->defer;
 128       g->defer = d->__next;
 129
 130       if (runtime_m () != NULL)
 131         runtime_freedefer (d);
 132
 133       /* We are returning from this function.  */
 134       *frame = 1;
 135
 136       return;
 137     }
 138
 139   /* This is some other defer function.  It was already run by the
 140      call to panic, or just above.  Rethrow the exception.  */
 141
 142   hdr = (struct _Unwind_Exception *) g->exception;
 143
 144 #ifdef LIBGO_SJLJ_EXCEPTIONS
 145   _Unwind_SjLj_Resume_or_Rethrow (hdr);
 146 #else
 147 #if defined(_LIBUNWIND_STD_ABI)
 148   _Unwind_RaiseException (hdr);
 149 #else
 150   _Unwind_Resume_or_Rethrow (hdr);
 151 #endif
 152 #endif
 153
 154   /* Rethrowing the exception should not return.  */
 155   abort();
 156 }
 157
 158 /* Unwind function calls until we reach the one which used a defer
 159    function which called recover.  Each function which uses a defer
 160    statement will have an exception handler, as shown above.  */
 161
 162 void
 163 __go_unwind_stack ()
 164 {
 165   struct _Unwind_Exception *hdr;
 166
 167   hdr = ((struct _Unwind_Exception *)
 168          __go_alloc (sizeof (struct _Unwind_Exception)));
 169   __builtin_memcpy (&hdr->exception_class, &__go_exception_class,
 170                     sizeof hdr->exception_class);
 171   hdr->exception_cleanup = NULL;
 172
 173   runtime_g ()->exception = hdr;
 174
 175 #ifdef __USING_SJLJ_EXCEPTIONS__
 176   _Unwind_SjLj_RaiseException (hdr);
 177 #else
 178   _Unwind_RaiseException (hdr);
 179 #endif
 180
 181   /* Raising an exception should not return.  */
 182   abort ();
 183 }
 184
 185 /* The rest of this code is really similar to gcc/unwind-c.c and
 186    libjava/exception.cc.  */
 187
 188 typedef struct
 189 {
 190   _Unwind_Ptr Start;
 191   _Unwind_Ptr LPStart;
 192   _Unwind_Ptr ttype_base;
 193   const unsigned char *TType;
 194   const unsigned char *action_table;
 195   unsigned char ttype_encoding;
 196   unsigned char call_site_encoding;
 197 } lsda_header_info;
 198
 199 static const unsigned char *
 200 parse_lsda_header (struct _Unwind_Context *context, const unsigned char *p,
 201                    lsda_header_info *info)
 202 {
 203   _uleb128_t tmp;
 204   unsigned char lpstart_encoding;
 205
 206   info->Start = (context ? _Unwind_GetRegionStart (context) : 0);
 207
 208   /* Find @LPStart, the base to which landing pad offsets are relative.  */
 209   lpstart_encoding = *p++;
 210   if (lpstart_encoding != DW_EH_PE_omit)
 211     p = read_encoded_value (context, lpstart_encoding, p, &info->LPStart);
 212   else
 213     info->LPStart = info->Start;
 214
 215   /* Find @TType, the base of the handler and exception spec type data.  */
 216   info->ttype_encoding = *p++;
 217   if (info->ttype_encoding != DW_EH_PE_omit)
 218     {
 219       p = read_uleb128 (p, &tmp);
 220       info->TType = p + tmp;
 221     }
 222   else
 223     info->TType = 0;
 224
 225   /* The encoding and length of the call-site table; the action table
 226      immediately follows.  */
 227   info->call_site_encoding = *p++;
 228   p = read_uleb128 (p, &tmp);
 229   info->action_table = p + tmp;
 230
 231   return p;
 232 }
 233
 234 /* The personality function is invoked when unwinding the stack due to
 235    a panic.  Its job is to find the cleanup and exception handlers to
 236    run.  We can't split the stack here, because we won't be able to
 237    unwind from that split.  */
 238
 239 #ifdef __ARM_EABI_UNWINDER__
 240 /* ARM EABI personality routines must also unwind the stack.  */
 241 #define CONTINUE_UNWINDING \
 242   do                                                            \
 243     {                                                           \
 244       if (__gnu_unwind_frame (ue_header, context) != _URC_OK)   \
 245         return _URC_FAILURE;                                    \
 246       return _URC_CONTINUE_UNWIND;                              \
 247     }                                                           \
 248   while (0)
 249 #else
 250 #define CONTINUE_UNWINDING return _URC_CONTINUE_UNWIND
 251 #endif
 252
 253 #ifdef __USING_SJLJ_EXCEPTIONS__
 254 #define PERSONALITY_FUNCTION    __gccgo_personality_sj0
 255 #define __builtin_eh_return_data_regno(x) x
 256 #else
 257 #define PERSONALITY_FUNCTION    __gccgo_personality_v0
 258 #endif
 259
 260 #ifdef __ARM_EABI_UNWINDER__
 261 _Unwind_Reason_Code
 262 PERSONALITY_FUNCTION (_Unwind_State, struct _Unwind_Exception *,
 263                       struct _Unwind_Context *)
 264   __attribute__ ((no_split_stack, flatten));
 265
 266 _Unwind_Reason_Code
 267 PERSONALITY_FUNCTION (_Unwind_State state,
 268                       struct _Unwind_Exception * ue_header,
 269                       struct _Unwind_Context * context)
 270 #else
 271 _Unwind_Reason_Code
 272 PERSONALITY_FUNCTION (int, _Unwind_Action, _Unwind_Exception_Class,
 273                       struct _Unwind_Exception *, struct _Unwind_Context *)
 274   __attribute__ ((no_split_stack, flatten));
 275
 276 _Unwind_Reason_Code
 277 PERSONALITY_FUNCTION (int version,
 278                       _Unwind_Action actions,
 279                       _Unwind_Exception_Class exception_class,
 280                       struct _Unwind_Exception *ue_header,
 281                       struct _Unwind_Context *context)
 282 #endif
 283 {
 284   lsda_header_info info;
 285   const unsigned char *language_specific_data, *p, *action_record;
 286   _Unwind_Ptr landing_pad, ip;
 287   int ip_before_insn = 0;
 288   _Bool is_foreign;
 289   G *g;
 290
 291 #ifdef __ARM_EABI_UNWINDER__
 292   _Unwind_Action actions;
 293
 294   switch (state & _US_ACTION_MASK)
 295     {
 296     case _US_VIRTUAL_UNWIND_FRAME:
 297       actions = _UA_SEARCH_PHASE;
 298       break;
 299
 300     case _US_UNWIND_FRAME_STARTING:
 301       actions = _UA_CLEANUP_PHASE;
 302       if (!(state & _US_FORCE_UNWIND)
 303           && ue_header->barrier_cache.sp == _Unwind_GetGR(context, 13))
 304         actions |= _UA_HANDLER_FRAME;
 305       break;
 306
 307     case _US_UNWIND_FRAME_RESUME:
 308       CONTINUE_UNWINDING;
 309       break;
 310
 311     default:
 312       abort();
 313     }
 314   actions |= state & _US_FORCE_UNWIND;
 315
 316   is_foreign = 0;
 317
 318   /* The dwarf unwinder assumes the context structure holds things like the
 319      function and LSDA pointers.  The ARM implementation caches these in
 320      the exception header (UCB).  To avoid rewriting everything we make the
 321      virtual IP register point at the UCB.  */
 322   ip = (_Unwind_Ptr) ue_header;
 323   _Unwind_SetGR (context, 12, ip);
 324 #else
 325   if (version != 1)
 326     return _URC_FATAL_PHASE1_ERROR;
 327
 328   is_foreign = exception_class != __go_exception_class;
 329 #endif
 330
 331   language_specific_data = (const unsigned char *)
 332     _Unwind_GetLanguageSpecificData (context);
 333
 334   /* If no LSDA, then there are no handlers or cleanups.  */
 335   if (! language_specific_data)
 336     CONTINUE_UNWINDING;
 337
 338   /* Parse the LSDA header.  */
 339   p = parse_lsda_header (context, language_specific_data, &info);
 340 #ifdef HAVE_GETIPINFO
 341   ip = _Unwind_GetIPInfo (context, &ip_before_insn);
 342 #else
 343   ip = _Unwind_GetIP (context);
 344 #endif
 345   if (! ip_before_insn)
 346     --ip;
 347   landing_pad = 0;
 348   action_record = NULL;
 349
 350 #ifdef __USING_SJLJ_EXCEPTIONS__
 351   /* The given "IP" is an index into the call-site table, with two
 352      exceptions -- -1 means no-action, and 0 means terminate.  But
 353      since we're using uleb128 values, we've not got random access
 354      to the array.  */
 355   if ((int) ip <= 0)
 356     return _URC_CONTINUE_UNWIND;
 357   else
 358     {
 359       _uleb128_t cs_lp, cs_action;
 360       do
 361         {
 362           p = read_uleb128 (p, &cs_lp);
 363           p = read_uleb128 (p, &cs_action);
 364         }
 365       while (--ip);
 366
 367       /* Can never have null landing pad for sjlj -- that would have
 368          been indicated by a -1 call site index.  */
 369       landing_pad = (_Unwind_Ptr)cs_lp + 1;
 370       if (cs_action)
 371         action_record = info.action_table + cs_action - 1;
 372       goto found_something;
 373     }
 374 #else
 375   /* Search the call-site table for the action associated with this IP.  */
 376   while (p < info.action_table)
 377     {
 378       _Unwind_Ptr cs_start, cs_len, cs_lp;
 379       _uleb128_t cs_action;
 380
 381       /* Note that all call-site encodings are "absolute" displacements.  */
 382       p = read_encoded_value (0, info.call_site_encoding, p, &cs_start);
 383       p = read_encoded_value (0, info.call_site_encoding, p, &cs_len);
 384       p = read_encoded_value (0, info.call_site_encoding, p, &cs_lp);
 385       p = read_uleb128 (p, &cs_action);
 386
 387       /* The table is sorted, so if we've passed the ip, stop.  */
 388       if (ip < info.Start + cs_start)
 389         p = info.action_table;
 390       else if (ip < info.Start + cs_start + cs_len)
 391         {
 392           if (cs_lp)
 393             landing_pad = info.LPStart + cs_lp;
 394           if (cs_action)
 395             action_record = info.action_table + cs_action - 1;
 396           goto found_something;
 397         }
 398     }
 399 #endif
 400
 401   /* IP is not in table.  No associated cleanups.  */
 402   CONTINUE_UNWINDING;
 403
 404  found_something:
 405   if (landing_pad == 0)
 406     {
 407       /* IP is present, but has a null landing pad.
 408          No handler to be run.  */
 409       CONTINUE_UNWINDING;
 410     }
 411
 412   if (actions & _UA_SEARCH_PHASE)
 413     {
 414       if (action_record == 0)
 415         {
 416           /* This indicates a cleanup rather than an exception
 417              handler.  */
 418           CONTINUE_UNWINDING;
 419         }
 420
 421       return _URC_HANDLER_FOUND;
 422     }
 423
 424   /* It's possible for g to be NULL here for an exception thrown by a
 425      language other than Go.  */
 426   g = runtime_g ();
 427   if (g == NULL)
 428     {
 429       if (!is_foreign)
 430         abort ();
 431     }
 432   else
 433     {
 434       g->exception = ue_header;
 435       g->is_foreign = is_foreign;
 436     }
 437
 438   _Unwind_SetGR (context, __builtin_eh_return_data_regno (0),
 439                  (_Unwind_Ptr) ue_header);
 440   _Unwind_SetGR (context, __builtin_eh_return_data_regno (1), 0);
 441   _Unwind_SetIP (context, landing_pad);
 442   return _URC_INSTALL_CONTEXT;
 443 }