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492d29ea1c
binutils-gdb/gdb/exceptions.c
Pedro Alves 492d29ea1c Split TRY_CATCH into TRY + CATCH 
This patch splits the TRY_CATCH macro into three, so that we go from
this:

~~~
  volatile gdb_exception ex;

  TRY_CATCH (ex, RETURN_MASK_ERROR)
    {
    }
  if (ex.reason < 0)
    {
    }
~~~

to this:

~~~
  TRY
    {
    }
  CATCH (ex, RETURN_MASK_ERROR)
    {
    }
  END_CATCH
~~~

Thus, we'll be getting rid of the local volatile exception object, and
declaring the caught exception in the catch block.

This allows reimplementing TRY/CATCH in terms of C++ exceptions when
building in C++ mode, while still allowing to build GDB in C mode
(using setjmp/longjmp), as a transition step.

TBC, after this patch, is it _not_ valid to have code between the TRY
and the CATCH blocks, like:

  TRY
    {
    }

  // some code here.

  CATCH (ex, RETURN_MASK_ERROR)
    {
    }
  END_CATCH

Just like it isn't valid to do that with C++'s native try/catch.

By switching to creating the exception object inside the CATCH block
scope, we can get rid of all the explicitly allocated volatile
exception objects all over the tree, and map the CATCH block more
directly to C++'s catch blocks.

The majority of the TRY_CATCH -> TRY+CATCH+END_CATCH conversion was
done with a script, rerun from scratch at every rebase, no manual
editing involved.  After the mechanical conversion, a few places
needed manual intervention, to fix preexisting cases where we were
using the exception object outside of the TRY_CATCH block, and cases
where we were using "else" after a 'if (ex.reason) < 0)' [a CATCH
after this patch].  The result was folded into this patch so that GDB
still builds at each incremental step.

END_CATCH is necessary for two reasons:

First, because we name the exception object in the CATCH block, which
requires creating a scope, which in turn must be closed somewhere.
Declaring the exception variable in the initializer field of a for
block, like:

  #define CATCH(EXCEPTION, mask) \
    for (struct gdb_exception EXCEPTION; \
         exceptions_state_mc_catch (&EXCEPTION, MASK); \
	 EXCEPTION = exception_none)

would avoid needing END_CATCH, but alas, in C mode, we build with C90,
which doesn't allow mixed declarations and code.

Second, because when TRY/CATCH are wired to real C++ try/catch, as
long as we need to handle cleanup chains, even if there's no CATCH
block that wants to catch the exception, we need for stop at every
frame in the unwind chain and run cleanups, then rethrow.  That will
be done in END_CATCH.

After we require C++, we'll still need TRY/CATCH/END_CATCH until
cleanups are completely phased out -- TRY/CATCH in C++ mode will
save/restore the current cleanup chain, like in C mode, and END_CATCH
catches otherwise uncaugh exceptions, runs cleanups and rethrows, so
that C++ cleanups and exceptions can coexist.

IMO, this still makes the TRY/CATCH code look a bit more like a
newcomer would expect, so IMO worth it even if we weren't considering
C++.

gdb/ChangeLog.
2015-03-07  Pedro Alves  <palves@redhat.com>

	* common/common-exceptions.c (struct catcher) <exception>: No
	longer a pointer to volatile exception.  Now an exception value.
	<mask>: Delete field.
	(exceptions_state_mc_init): Remove all parameters.  Adjust.
	(exceptions_state_mc): No longer pop the catcher here.
	(exceptions_state_mc_catch): New function.
	(throw_exception): Adjust.
	* common/common-exceptions.h (exceptions_state_mc_init): Remove
	all parameters.
	(exceptions_state_mc_catch): Declare.
	(TRY_CATCH): Rename to ...
	(TRY): ... this.  Remove EXCEPTION and MASK parameters.
	(CATCH, END_CATCH): New.
	All callers adjusted.

gdb/gdbserver/ChangeLog:
2015-03-07  Pedro Alves  <palves@redhat.com>

	Adjust all callers of TRY_CATCH to use TRY/CATCH/END_CATCH
	instead.
2015-03-07 15:14:14 +00:00

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/* Exception (throw catch) mechanism, for GDB, the GNU debugger.
Copyright (C) 1986-2015 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 "defs.h"
#include "exceptions.h"
#include "breakpoint.h"
#include "target.h"
#include "inferior.h"
#include "annotate.h"
#include "ui-out.h"
#include "serial.h"
#include "gdbthread.h"
void
prepare_to_throw_exception (void)
{
clear_quit_flag ();
immediate_quit = 0;
}
static void
print_flush (void)
{
struct serial *gdb_stdout_serial;
if (deprecated_error_begin_hook)
deprecated_error_begin_hook ();
if (target_supports_terminal_ours ())
target_terminal_ours ();
/* We want all output to appear now, before we print the error. We
have 3 levels of buffering we have to flush (it's possible that
some of these should be changed to flush the lower-level ones
too): */
/* 1. The _filtered buffer. */
if (filtered_printing_initialized ())
wrap_here ("");
/* 2. The stdio buffer. */
gdb_flush (gdb_stdout);
gdb_flush (gdb_stderr);
/* 3. The system-level buffer. */
gdb_stdout_serial = serial_fdopen (1);
if (gdb_stdout_serial)
{
serial_drain_output (gdb_stdout_serial);
serial_un_fdopen (gdb_stdout_serial);
}
annotate_error_begin ();
}
static void
print_exception (struct ui_file *file, struct gdb_exception e)
{
/* KLUGE: cagney/2005-01-13: Write the string out one line at a time
as that way the MI's behavior is preserved. */
const char *start;
const char *end;
for (start = e.message; start != NULL; start = end)
{
end = strchr (start, '\n');
if (end == NULL)
fputs_filtered (start, file);
else
{
end++;
ui_file_write (file, start, end - start);
}
}
fprintf_filtered (file, "\n");
/* Now append the annotation. */
switch (e.reason)
{
case RETURN_QUIT:
annotate_quit ();
break;
case RETURN_ERROR:
/* Assume that these are all errors. */
annotate_error ();
break;
default:
internal_error (__FILE__, __LINE__, _("Bad switch."));
}
}
void
exception_print (struct ui_file *file, struct gdb_exception e)
{
if (e.reason < 0 && e.message != NULL)
{
print_flush ();
print_exception (file, e);
}
}
void
exception_fprintf (struct ui_file *file, struct gdb_exception e,
const char *prefix, ...)
{
if (e.reason < 0 && e.message != NULL)
{
va_list args;
print_flush ();
/* Print the prefix. */
va_start (args, prefix);
vfprintf_filtered (file, prefix, args);
va_end (args);
print_exception (file, e);
}
}
/* Call FUNC(UIOUT, FUNC_ARGS) but wrapped within an exception
handler. If an exception (enum return_reason) is thrown using
throw_exception() than all cleanups installed since
catch_exceptions() was entered are invoked, the (-ve) exception
value is then returned by catch_exceptions. If FUNC() returns
normally (with a positive or zero return value) then that value is
returned by catch_exceptions(). It is an internal_error() for
FUNC() to return a negative value.
See exceptions.h for further usage details.
Must not be called with immediate_quit in effect (bad things might
happen, say we got a signal in the middle of a memcpy to quit_return).
This is an OK restriction; with very few exceptions immediate_quit can
be replaced by judicious use of QUIT. */
/* MAYBE: cagney/1999-11-05: catch_errors() in conjunction with
error() et al. could maintain a set of flags that indicate the
current state of each of the longjmp buffers. This would give the
longjmp code the chance to detect a longjmp botch (before it gets
to longjmperror()). Prior to 1999-11-05 this wasn't possible as
code also randomly used a SET_TOP_LEVEL macro that directly
initialized the longjmp buffers. */
int
catch_exceptions (struct ui_out *uiout,
catch_exceptions_ftype *func,
void *func_args,
return_mask mask)
{
return catch_exceptions_with_msg (uiout, func, func_args, NULL, mask);
}
int
catch_exceptions_with_msg (struct ui_out *func_uiout,
catch_exceptions_ftype *func,
void *func_args,
char **gdberrmsg,
return_mask mask)
{
struct gdb_exception exception = exception_none;
volatile int val = 0;
struct ui_out *saved_uiout;
/* Save and override the global ``struct ui_out'' builder. */
saved_uiout = current_uiout;
current_uiout = func_uiout;
TRY
{
val = (*func) (current_uiout, func_args);
}
CATCH (ex, RETURN_MASK_ALL)
{
exception = ex;
}
END_CATCH
/* Restore the global builder. */
current_uiout = saved_uiout;
if (exception.reason < 0 && (mask & RETURN_MASK (exception.reason)) == 0)
{
/* The caller didn't request that the event be caught.
Rethrow. */
throw_exception (exception);
}
exception_print (gdb_stderr, exception);
gdb_assert (val >= 0);
gdb_assert (exception.reason <= 0);
if (exception.reason < 0)
{
/* If caller wants a copy of the low-level error message, make
one. This is used in the case of a silent error whereby the
caller may optionally want to issue the message. */
if (gdberrmsg != NULL)
{
if (exception.message != NULL)
*gdberrmsg = xstrdup (exception.message);
else
*gdberrmsg = NULL;
}
return exception.reason;
}
return val;
}
/* This function is superseded by catch_exceptions(). */
int
catch_errors (catch_errors_ftype *func, void *func_args, char *errstring,
return_mask mask)
{
struct gdb_exception exception = exception_none;
volatile int val = 0;
struct ui_out *saved_uiout;
/* Save the global ``struct ui_out'' builder. */
saved_uiout = current_uiout;
TRY
{
val = func (func_args);
}
CATCH (ex, RETURN_MASK_ALL)
{
exception = ex;
}
END_CATCH
/* Restore the global builder. */
current_uiout = saved_uiout;
if (exception.reason < 0 && (mask & RETURN_MASK (exception.reason)) == 0)
{
/* The caller didn't request that the event be caught.
Rethrow. */
throw_exception (exception);
}
exception_fprintf (gdb_stderr, exception, "%s", errstring);
if (exception.reason != 0)
return 0;
return val;
}
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