common-exceptions.c

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/* Exception (throw catch) mechanism, for GDB, the GNU debugger.

   Copyright (C) 1986-2018 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "common-defs.h"
#include "common-exceptions.h"

const struct gdb_exception exception_none = { (enum return_reason) 0, GDB_NO_ERROR, NULL };

/* Possible catcher states.  */
enum catcher_state {
  /* Initial state, a new catcher has just been created.  */
  CATCHER_CREATED,
  /* The catch code is running.  */
  CATCHER_RUNNING,
  CATCHER_RUNNING_1,
  /* The catch code threw an exception.  */
  CATCHER_ABORTING
};

/* Possible catcher actions.  */
enum catcher_action {
  CATCH_ITER,
  CATCH_ITER_1,
  CATCH_THROWING
};

struct catcher
{
  enum catcher_state state;
  /* Jump buffer pointing back at the exception handler.  */
  jmp_buf buf;
  /* Status buffer belonging to the exception handler.  */
  struct gdb_exception exception;
  struct cleanup *saved_cleanup_chain;
  /* Back link.  */
  struct catcher *prev;
};

/* Where to go for throw_exception().  */
static struct catcher *current_catcher;

#if GDB_XCPT == GDB_XCPT_SJMP

/* Return length of current_catcher list.  */

static int
catcher_list_size (void)
{
  int size;
  struct catcher *catcher;

  for (size = 0, catcher = current_catcher;
       catcher != NULL;
       catcher = catcher->prev)
    ++size;

  return size;
}

#endif

jmp_buf *
exceptions_state_mc_init (void)
{
  struct catcher *new_catcher = XCNEW (struct catcher);

  /* Start with no exception.  */
  new_catcher->exception = exception_none;

  /* Prevent error/quit during FUNC from calling cleanups established
     prior to here.  */
  new_catcher->saved_cleanup_chain = save_cleanups ();

  /* Push this new catcher on the top.  */
  new_catcher->prev = current_catcher;
  current_catcher = new_catcher;
  new_catcher->state = CATCHER_CREATED;

  return &new_catcher->buf;
}

static void
catcher_pop (void)
{
  struct catcher *old_catcher = current_catcher;

  current_catcher = old_catcher->prev;

  /* Restore the cleanup chain, the error/quit messages, and the uiout
     builder, to their original states.  */

  restore_cleanups (old_catcher->saved_cleanup_chain);

  xfree (old_catcher);
}

/* Catcher state machine.  Returns non-zero if the m/c should be run
   again, zero if it should abort.  */

static int
exceptions_state_mc (enum catcher_action action)
{
  switch (current_catcher->state)
    {
    case CATCHER_CREATED:
      switch (action)
    {
    case CATCH_ITER:
      /* Allow the code to run the catcher.  */
      current_catcher->state = CATCHER_RUNNING;
      return 1;
    default:
      internal_error (__FILE__, __LINE__, _("bad state"));
    }
    case CATCHER_RUNNING:
      switch (action)
    {
    case CATCH_ITER:
      /* No error/quit has occured.  */
      return 0;
    case CATCH_ITER_1:
      current_catcher->state = CATCHER_RUNNING_1;
      return 1;
    case CATCH_THROWING:
      current_catcher->state = CATCHER_ABORTING;
      /* See also throw_exception.  */
      return 1;
    default:
      internal_error (__FILE__, __LINE__, _("bad switch"));
    }
    case CATCHER_RUNNING_1:
      switch (action)
    {
    case CATCH_ITER:
      /* The did a "break" from the inner while loop.  */
      return 0;
    case CATCH_ITER_1:
      current_catcher->state = CATCHER_RUNNING;
      return 0;
    case CATCH_THROWING:
      current_catcher->state = CATCHER_ABORTING;
      /* See also throw_exception.  */
      return 1;
    default:
      internal_error (__FILE__, __LINE__, _("bad switch"));
    }
    case CATCHER_ABORTING:
      switch (action)
    {
    case CATCH_ITER:
      {
        /* Exit normally if this catcher can handle this
           exception.  The caller analyses the func return
           values.  */
        return 0;
      }
    default:
      internal_error (__FILE__, __LINE__, _("bad state"));
    }
    default:
      internal_error (__FILE__, __LINE__, _("bad switch"));
    }
}

int
exceptions_state_mc_catch (struct gdb_exception *exception,
               int mask)
{
  *exception = current_catcher->exception;
  catcher_pop ();

  if (exception->reason < 0)
    {
      if (mask & RETURN_MASK (exception->reason))
    {
      /* Exit normally and let the caller handle the
         exception.  */
      return 1;
    }

      /* The caller didn't request that the event be caught, relay the
     event to the next exception_catch/CATCH_SJLJ.  */
      throw_exception_sjlj (*exception);
    }

  /* No exception was thrown.  */
  return 0;
}

int
exceptions_state_mc_action_iter (void)
{
  return exceptions_state_mc (CATCH_ITER);
}

int
exceptions_state_mc_action_iter_1 (void)
{
  return exceptions_state_mc (CATCH_ITER_1);
}

#if GDB_XCPT != GDB_XCPT_SJMP

/* How many nested TRY blocks we have.  See exception_messages and
   throw_it.  */

static int try_scope_depth;

/* Called on entry to a TRY scope.  */

void *
exception_try_scope_entry (void)
{
  ++try_scope_depth;
  return (void *) save_cleanups ();
}

/* Called on exit of a TRY scope, either normal exit or exception
   exit.  */

void
exception_try_scope_exit (void *saved_state)
{
  restore_cleanups ((struct cleanup *) saved_state);
  --try_scope_depth;
}

/* Called by the default catch block.  IOW, we'll get here before
   jumping out to the next outermost scope an exception if a GDB
   exception is not caught.  */

void
exception_rethrow (void)
{
  /* Run this scope's cleanups before re-throwing to the next
     outermost scope.  */
  do_cleanups (all_cleanups ());
  throw;
}

/* Copy the 'gdb_exception' portion of FROM to TO.  */

static void
gdb_exception_sliced_copy (struct gdb_exception *to, const struct gdb_exception *from)
{
  *to = *from;
}

#endif /* !GDB_XCPT_SJMP */

/* Return EXCEPTION to the nearest containing CATCH_SJLJ block.  */

void
throw_exception_sjlj (struct gdb_exception exception)
{
  do_cleanups (all_cleanups ());

  /* Jump to the nearest CATCH_SJLJ block, communicating REASON to
     that call via setjmp's return value.  Note that REASON can't be
     zero, by definition in common-exceptions.h.  */
  exceptions_state_mc (CATCH_THROWING);
  current_catcher->exception = exception;
  longjmp (current_catcher->buf, exception.reason);
}

#if GDB_XCPT != GDB_XCPT_SJMP

/* Implementation of throw_exception that uses C++ try/catch.  */

static ATTRIBUTE_NORETURN void
throw_exception_cxx (struct gdb_exception exception)
{
  do_cleanups (all_cleanups ());

  if (exception.reason == RETURN_QUIT)
    {
      gdb_exception_RETURN_MASK_QUIT ex;

      gdb_exception_sliced_copy (&ex, &exception);
      throw ex;
    }
  else if (exception.reason == RETURN_ERROR)
    {
      gdb_exception_RETURN_MASK_ERROR ex;

      gdb_exception_sliced_copy (&ex, &exception);
      throw ex;
    }
  else
    gdb_assert_not_reached ("invalid return reason");
}

#endif

void
throw_exception (struct gdb_exception exception)
{
#if GDB_XCPT == GDB_XCPT_SJMP
  throw_exception_sjlj (exception);
#else
  throw_exception_cxx (exception);
#endif
}

/* A stack of exception messages.
   This is needed to handle nested calls to throw_it: we don't want to
   xfree space for a message before it's used.
   This can happen if we throw an exception during a cleanup:
   An outer TRY_CATCH may have an exception message it wants to print,
   but while doing cleanups further calls to throw_it are made.

   This is indexed by the size of the current_catcher list.
   It is a dynamically allocated array so that we don't care how deeply
   GDB nests its TRY_CATCHs.  */
static char **exception_messages;

/* The number of currently allocated entries in exception_messages.  */
static int exception_messages_size;

static void ATTRIBUTE_NORETURN ATTRIBUTE_PRINTF (3, 0)
throw_it (enum return_reason reason, enum errors error, const char *fmt,
      va_list ap)
{
  struct gdb_exception e;
  char *new_message;
#if GDB_XCPT == GDB_XCPT_SJMP
  int depth = catcher_list_size ();
#else
  int depth = try_scope_depth;
#endif

  gdb_assert (depth > 0);

  /* Note: The new message may use an old message's text.  */
  new_message = xstrvprintf (fmt, ap);

  if (depth > exception_messages_size)
    {
      int old_size = exception_messages_size;

      exception_messages_size = depth + 10;
      exception_messages = XRESIZEVEC (char *, exception_messages,
                       exception_messages_size);
      memset (exception_messages + old_size, 0,
          (exception_messages_size - old_size) * sizeof (char *));
    }

  xfree (exception_messages[depth - 1]);
  exception_messages[depth - 1] = new_message;

  /* Create the exception.  */
  e.reason = reason;
  e.error = error;
  e.message = new_message;

  /* Throw the exception.  */
  throw_exception (e);
}

void
throw_verror (enum errors error, const char *fmt, va_list ap)
{
  throw_it (RETURN_ERROR, error, fmt, ap);
}

void
throw_vquit (const char *fmt, va_list ap)
{
  throw_it (RETURN_QUIT, GDB_NO_ERROR, fmt, ap);
}

void
throw_error (enum errors error, const char *fmt, ...)
{
  va_list args;

  va_start (args, fmt);
  throw_verror (error, fmt, args);
  va_end (args);
}

void
throw_quit (const char *fmt, ...)
{
  va_list args;

  va_start (args, fmt);
  throw_vquit (fmt, args);
  va_end (args);
}