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/* go-unwind.c -- unwind the stack for panic/recover.

   Copyright 2010 The Go Authors. All rights reserved.

   Use of this source code is governed by a BSD-style

   license that can be found in the LICENSE file.  */

#include "config.h"

#include <stdlib.h>

#include <unistd.h>

#include "unwind.h"

#define NO_SIZE_OF_ENCODED_VALUE

#include "unwind-pe.h"

#include "runtime.h"

#include "go-alloc.h"

#include "go-defer.h"

#include "go-panic.h"

/* The code for a Go exception.  */

#ifdef __ARM_EABI_UNWINDER__

static const _Unwind_Exception_Class __go_exception_class =

  { 'G', 'N', 'U', 'C', 'G', 'O', '\0', '\0' };

#else

static const _Unwind_Exception_Class __go_exception_class =

  ((((((((_Unwind_Exception_Class) 'G'

         << 8 | (_Unwind_Exception_Class) 'N')

        << 8 | (_Unwind_Exception_Class) 'U')

       << 8 | (_Unwind_Exception_Class) 'C')

      << 8 | (_Unwind_Exception_Class) 'G')

     << 8 | (_Unwind_Exception_Class) 'O')

    << 8 | (_Unwind_Exception_Class) '\0')

   << 8 | (_Unwind_Exception_Class) '\0');

#endif

/* This function is called by exception handlers used when unwinding

   the stack after a recovered panic.  The exception handler looks

   like this:

     __go_check_defer (frame);

     return;

   If we have not yet reached the frame we are looking for, we

   continue unwinding.  */

void

__go_check_defer (_Bool *frame)

{

  G *g;

  struct _Unwind_Exception *hdr;

  g = runtime_g ();

  if (g == NULL)

    {

      /* Some other language has thrown an exception.  We know there

         are no defer handlers, so there is nothing to do.  */

    }

  else if (g->is_foreign)

    {

      struct __go_panic_stack *n;

      _Bool was_recovered;

      /* Some other language has thrown an exception.  We need to run

         the local defer handlers.  If they call recover, we stop

         unwinding the stack here.  */

      n = ((struct __go_panic_stack *)

           __go_alloc (sizeof (struct __go_panic_stack)));

      n->__arg.__type_descriptor = NULL;

      n->__arg.__object = NULL;

      n->__was_recovered = 0;

      n->__is_foreign = 1;

      n->__next = g->panic;

      g->panic = n;

      while (1)

        {

          struct __go_defer_stack *d;

          void (*pfn) (void *);

          d = g->defer;

          if (d == NULL || d->__frame != frame || d->__pfn == NULL)

            break;

          pfn = d->__pfn;

          g->defer = d->__next;

          (*pfn) (d->__arg);

          __go_free (d);

          if (n->__was_recovered)

            {

              /* The recover function caught the panic thrown by some

                 other language.  */

              break;

            }

        }

      was_recovered = n->__was_recovered;

      g->panic = n->__next;

      __go_free (n);

      if (was_recovered)

        {

          /* Just return and continue executing Go code.  */

          *frame = 1;

          return;

        }

      /* We are panicing through this function.  */

      *frame = 0;

    }

  else if (g->defer != NULL

           && g->defer->__pfn == NULL

           && g->defer->__frame == frame)

    {

      struct __go_defer_stack *d;

      /* This is the defer function which called recover.  Simply

         return to stop the stack unwind, and let the Go code continue

         to execute.  */

      d = g->defer;

      g->defer = d->__next;

      __go_free (d);

      /* We are returning from this function.  */

      *frame = 1;

      return;

    }

  /* This is some other defer function.  It was already run by the

     call to panic, or just above.  Rethrow the exception.  */

  hdr = (struct _Unwind_Exception *) g->exception;

#ifdef LIBGO_SJLJ_EXCEPTIONS

  _Unwind_SjLj_Resume_or_Rethrow (hdr);

#else

#if defined(_LIBUNWIND_STD_ABI)

  _Unwind_RaiseException (hdr);

#else

  _Unwind_Resume_or_Rethrow (hdr);

#endif

#endif

  /* Rethrowing the exception should not return.  */

  abort();

}

/* Unwind function calls until we reach the one which used a defer

   function which called recover.  Each function which uses a defer

   statement will have an exception handler, as shown above.  */

void

__go_unwind_stack ()

{

  struct _Unwind_Exception *hdr;

  hdr = ((struct _Unwind_Exception *)

         __go_alloc (sizeof (struct _Unwind_Exception)));

  __builtin_memcpy (&hdr->exception_class, &__go_exception_class,

                    sizeof hdr->exception_class);

  hdr->exception_cleanup = NULL;

  runtime_g ()->exception = hdr;

#ifdef __USING_SJLJ_EXCEPTIONS__

  _Unwind_SjLj_RaiseException (hdr);

#else

  _Unwind_RaiseException (hdr);

#endif

  /* Raising an exception should not return.  */

  abort ();

}

/* The rest of this code is really similar to gcc/unwind-c.c and

   libjava/exception.cc.  */

typedef struct

{

  _Unwind_Ptr Start;

  _Unwind_Ptr LPStart;

  _Unwind_Ptr ttype_base;

  const unsigned char *TType;

  const unsigned char *action_table;

  unsigned char ttype_encoding;

  unsigned char call_site_encoding;

} lsda_header_info;

static const unsigned char *

parse_lsda_header (struct _Unwind_Context *context, const unsigned char *p,

                   lsda_header_info *info)

{

  _uleb128_t tmp;

  unsigned char lpstart_encoding;

  info->Start = (context ? _Unwind_GetRegionStart (context) : 0);

  /* Find @LPStart, the base to which landing pad offsets are relative.  */

  lpstart_encoding = *p++;

  if (lpstart_encoding != DW_EH_PE_omit)

    p = read_encoded_value (context, lpstart_encoding, p, &info->LPStart);

  else

    info->LPStart = info->Start;

  /* Find @TType, the base of the handler and exception spec type data.  */

  info->ttype_encoding = *p++;

  if (info->ttype_encoding != DW_EH_PE_omit)

    {

      p = read_uleb128 (p, &tmp);

      info->TType = p + tmp;

    }

  else

    info->TType = 0;

  /* The encoding and length of the call-site table; the action table

     immediately follows.  */

  info->call_site_encoding = *p++;

  p = read_uleb128 (p, &tmp);

  info->action_table = p + tmp;

  return p;

}

/* The personality function is invoked when unwinding the stack due to

   a panic.  Its job is to find the cleanup and exception handlers to

   run.  We can't split the stack here, because we won't be able to

   unwind from that split.  */

#ifdef __ARM_EABI_UNWINDER__

/* ARM EABI personality routines must also unwind the stack.  */

#define CONTINUE_UNWINDING \

  do                                                            \

    {                                                           \

      if (__gnu_unwind_frame (ue_header, context) != _URC_OK)   \

        return _URC_FAILURE;                                    \

      return _URC_CONTINUE_UNWIND;                              \

    }                                                           \

  while (0)

#else

#define CONTINUE_UNWINDING return _URC_CONTINUE_UNWIND

#endif

#ifdef __USING_SJLJ_EXCEPTIONS__

#define PERSONALITY_FUNCTION    __gccgo_personality_sj0

#define __builtin_eh_return_data_regno(x) x

#else

#define PERSONALITY_FUNCTION    __gccgo_personality_v0

#endif

#ifdef __ARM_EABI_UNWINDER__

_Unwind_Reason_Code

PERSONALITY_FUNCTION (_Unwind_State, struct _Unwind_Exception *,

                      struct _Unwind_Context *)

  __attribute__ ((no_split_stack, flatten));

_Unwind_Reason_Code

PERSONALITY_FUNCTION (_Unwind_State state,

                      struct _Unwind_Exception * ue_header,

                      struct _Unwind_Context * context)

#else

_Unwind_Reason_Code

PERSONALITY_FUNCTION (int, _Unwind_Action, _Unwind_Exception_Class,

                      struct _Unwind_Exception *, struct _Unwind_Context *)

  __attribute__ ((no_split_stack, flatten));

_Unwind_Reason_Code

PERSONALITY_FUNCTION (int version,

                      _Unwind_Action actions,

                      _Unwind_Exception_Class exception_class,

                      struct _Unwind_Exception *ue_header,

                      struct _Unwind_Context *context)

#endif

{

  lsda_header_info info;

  const unsigned char *language_specific_data, *p, *action_record;

  _Unwind_Ptr landing_pad, ip;

  int ip_before_insn = 0;

  _Bool is_foreign;

  G *g;

#ifdef __ARM_EABI_UNWINDER__

  _Unwind_Action actions;

  switch (state & _US_ACTION_MASK)

    {

    case _US_VIRTUAL_UNWIND_FRAME:

      actions = _UA_SEARCH_PHASE;

      break;

    case _US_UNWIND_FRAME_STARTING:

      actions = _UA_CLEANUP_PHASE;

      if (!(state & _US_FORCE_UNWIND)

          && ue_header->barrier_cache.sp == _Unwind_GetGR(context, 13))

        actions |= _UA_HANDLER_FRAME;

      break;

    case _US_UNWIND_FRAME_RESUME:

      CONTINUE_UNWINDING;

      break;

    default:

      abort();

    }

  actions |= state & _US_FORCE_UNWIND;

  is_foreign = 0;

  /* The dwarf unwinder assumes the context structure holds things like the

     function and LSDA pointers.  The ARM implementation caches these in

     the exception header (UCB).  To avoid rewriting everything we make the

     virtual IP register point at the UCB.  */

  ip = (_Unwind_Ptr) ue_header;

  _Unwind_SetGR (context, 12, ip);

#else

  if (version != 1)

    return _URC_FATAL_PHASE1_ERROR;

  is_foreign = exception_class != __go_exception_class;

#endif

  language_specific_data = (const unsigned char *)

    _Unwind_GetLanguageSpecificData (context);

  /* If no LSDA, then there are no handlers or cleanups.  */

  if (! language_specific_data)

    CONTINUE_UNWINDING;

  /* Parse the LSDA header.  */

  p = parse_lsda_header (context, language_specific_data, &info);

#ifdef HAVE_GETIPINFO

  ip = _Unwind_GetIPInfo (context, &ip_before_insn);

#else

  ip = _Unwind_GetIP (context);

#endif

  if (! ip_before_insn)

    --ip;

  landing_pad = 0;

  action_record = NULL;

#ifdef __USING_SJLJ_EXCEPTIONS__

  /* The given "IP" is an index into the call-site table, with two

     exceptions -- -1 means no-action, and 0 means terminate.  But

     since we're using uleb128 values, we've not got random access

     to the array.  */

  if ((int) ip <= 0)

    return _URC_CONTINUE_UNWIND;

  else

    {

      _uleb128_t cs_lp, cs_action;

      do

        {

          p = read_uleb128 (p, &cs_lp);

          p = read_uleb128 (p, &cs_action);

        }

      while (--ip);

      /* Can never have null landing pad for sjlj -- that would have

         been indicated by a -1 call site index.  */

      landing_pad = (_Unwind_Ptr)cs_lp + 1;

      if (cs_action)

        action_record = info.action_table + cs_action - 1;

      goto found_something;

    }

#else

  /* Search the call-site table for the action associated with this IP.  */

  while (p < info.action_table)

    {

      _Unwind_Ptr cs_start, cs_len, cs_lp;

      _uleb128_t cs_action;

      /* Note that all call-site encodings are "absolute" displacements.  */

      p = read_encoded_value (0, info.call_site_encoding, p, &cs_start);

      p = read_encoded_value (0, info.call_site_encoding, p, &cs_len);

      p = read_encoded_value (0, info.call_site_encoding, p, &cs_lp);

      p = read_uleb128 (p, &cs_action);

      /* The table is sorted, so if we've passed the ip, stop.  */

      if (ip < info.Start + cs_start)

        p = info.action_table;

      else if (ip < info.Start + cs_start + cs_len)

        {

          if (cs_lp)

            landing_pad = info.LPStart + cs_lp;

          if (cs_action)

            action_record = info.action_table + cs_action - 1;

          goto found_something;

        }

    }

#endif

  /* IP is not in table.  No associated cleanups.  */

  CONTINUE_UNWINDING;

 found_something:

  if (landing_pad == 0)

    {

      /* IP is present, but has a null landing pad.

         No handler to be run.  */

      CONTINUE_UNWINDING;

    }

  if (actions & _UA_SEARCH_PHASE)

    {

      if (action_record == 0)

        {

          /* This indicates a cleanup rather than an exception

             handler.  */

          CONTINUE_UNWINDING;

        }

      return _URC_HANDLER_FOUND;

    }

  /* It's possible for g to be NULL here for an exception thrown by a

     language other than Go.  */

  g = runtime_g ();

  if (g == NULL)

    {

      if (!is_foreign)

        abort ();

    }

  else

    {

      g->exception = ue_header;

      g->is_foreign = is_foreign;

    }

  _Unwind_SetGR (context, __builtin_eh_return_data_regno (0),

                 (_Unwind_Ptr) ue_header);

  _Unwind_SetGR (context, __builtin_eh_return_data_regno (1), 0);

  _Unwind_SetIP (context, landing_pad);

  return _URC_INSTALL_CONTEXT;

}