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/* go-recover.c -- support for the go recover function.

   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 "runtime.h"

#include "interface.h"

#include "go-panic.h"

#include "go-defer.h"

/* This is called by a thunk to see if the real function should be

   permitted to recover a panic value.  Recovering a value is

   permitted if the thunk was called directly by defer.  RETADDR is

   the return address of the function which is calling

   __go_can_recover--this is, the thunk.  */

_Bool

__go_can_recover (const void* retaddr)

{

  G *g;

  struct __go_defer_stack *d;

  const char* ret;

  const char* dret;

  g = runtime_g ();

  d = g->defer;

  if (d == NULL)

    return 0;

  /* The panic which this function would recover is the one on the top

     of the panic stack.  We do not want to recover it if that panic

     was on the top of the panic stack when this function was

     deferred.  */

  if (d->__panic == g->panic)

    return 0;

  /* D->__RETADDR is the address of a label immediately following the

     call to the thunk.  We can recover a panic if that is the same as

     the return address of the thunk.  We permit a bit of slack in

     case there is any code between the function return and the label,

     such as an instruction to adjust the stack pointer.  */

  ret = (const char *) retaddr;

#ifdef __sparc__

  /* On SPARC the address we get, from __builtin_return_address, is

     the address of the call instruction.  Adjust forward, also

     skipping the delayed instruction following the call.  */

  ret += 8;

#endif

  dret = (const char *) d->__retaddr;

  return ret <= dret && ret + 16 >= dret;

}

/* This is only called when it is valid for the caller to recover the

   value on top of the panic stack, if there is one.  */

struct __go_empty_interface

__go_recover ()

{

  G *g;

  struct __go_panic_stack *p;

  g = runtime_g ();

  if (g->panic == NULL || g->panic->__was_recovered)

    {

      struct __go_empty_interface ret;

      ret.__type_descriptor = NULL;

      ret.__object = NULL;

      return ret;

    }

  p = g->panic;

  p->__was_recovered = 1;

  return p->__arg;

}