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.

1 files changed, 25 insertions, 17 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 1e70d126614..124e370aa48 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -6479,7 +6479,6 @@ type_from_tag (struct value *tag)
 struct value *
 ada_tag_value_at_base_address (struct value *obj)
 {
-  volatile struct gdb_exception e;
   struct value *val;
   LONGEST offset_to_top = 0;
   struct type *ptr_type, *obj_type;
@@ -6514,13 +6513,16 @@ ada_tag_value_at_base_address (struct value *obj)
      see ada_tag_name for more details.  We do not print the error
      message for the same reason.  */
 
-  TRY_CATCH (e, RETURN_MASK_ERROR)
+  TRY
     {
       offset_to_top = value_as_long (value_ind (value_ptradd (val, -2)));
     }
 
-  if (e.reason < 0)
-    return obj;
+  CATCH (e, RETURN_MASK_ERROR)
+    {
+      return obj;
+    }
+  END_CATCH
 
   /* If offset is null, nothing to do.  */
 
@@ -6632,7 +6634,6 @@ ada_tag_name_from_tsd (struct value *tsd)
 const char *
 ada_tag_name (struct value *tag)
 {
-  volatile struct gdb_exception e;
   char *name = NULL;
 
   if (!ada_is_tag_type (value_type (tag)))
@@ -6647,13 +6648,17 @@ ada_tag_name (struct value *tag)
      We also do not print the error message either (which often is very
      low-level (Eg: "Cannot read memory at 0x[...]"), but instead let
      the caller print a more meaningful message if necessary.  */
-  TRY_CATCH (e, RETURN_MASK_ERROR)
+  TRY
     {
       struct value *tsd = ada_get_tsd_from_tag (tag);
 
       if (tsd != NULL)
 	name = ada_tag_name_from_tsd (tsd);
     }
+  CATCH (e, RETURN_MASK_ERROR)
+    {
+    }
+  END_CATCH
 
   return name;
 }
@@ -11817,19 +11822,19 @@ static CORE_ADDR
 ada_exception_name_addr (enum ada_exception_catchpoint_kind ex,
                          struct breakpoint *b)
 {
-  volatile struct gdb_exception e;
   CORE_ADDR result = 0;
 
-  TRY_CATCH (e, RETURN_MASK_ERROR)
+  TRY
     {
       result = ada_exception_name_addr_1 (ex, b);
     }
 
-  if (e.reason < 0)
+  CATCH (e, RETURN_MASK_ERROR)
     {
       warning (_("failed to get exception name: %s"), e.message);
       return 0;
     }
+  END_CATCH
 
   return result;
 }
@@ -11929,16 +11934,15 @@ create_excep_cond_exprs (struct ada_catchpoint *c)
 
       if (!bl->shlib_disabled)
 	{
-	  volatile struct gdb_exception e;
 	  const char *s;
 
 	  s = cond_string;
-	  TRY_CATCH (e, RETURN_MASK_ERROR)
+	  TRY
 	    {
 	      exp = parse_exp_1 (&s, bl->address,
 				 block_for_pc (bl->address), 0);
 	    }
-	  if (e.reason < 0)
+	  CATCH (e, RETURN_MASK_ERROR)
 	    {
 	      warning (_("failed to reevaluate internal exception condition "
 			 "for catchpoint %d: %s"),
@@ -11951,6 +11955,7 @@ create_excep_cond_exprs (struct ada_catchpoint *c)
 		 to NULL.  */
 	      exp = NULL;
 	    }
+	  END_CATCH
 	}
 
       ada_loc->excep_cond_expr = exp;
@@ -12014,7 +12019,6 @@ should_stop_exception (const struct bp_location *bl)
   struct ada_catchpoint *c = (struct ada_catchpoint *) bl->owner;
   const struct ada_catchpoint_location *ada_loc
     = (const struct ada_catchpoint_location *) bl;
-  volatile struct gdb_exception ex;
   int stop;
 
   /* With no specific exception, should always stop.  */
@@ -12029,7 +12033,7 @@ should_stop_exception (const struct bp_location *bl)
     }
 
   stop = 1;
-  TRY_CATCH (ex, RETURN_MASK_ALL)
+  TRY
     {
       struct value *mark;
 
@@ -12037,9 +12041,13 @@ should_stop_exception (const struct bp_location *bl)
       stop = value_true (evaluate_expression (ada_loc->excep_cond_expr));
       value_free_to_mark (mark);
     }
-  if (ex.reason < 0)
-    exception_fprintf (gdb_stderr, ex,
-		       _("Error in testing exception condition:\n"));
+  CATCH (ex, RETURN_MASK_ALL)
+    {
+      exception_fprintf (gdb_stderr, ex,
+			 _("Error in testing exception condition:\n"));
+    }
+  END_CATCH
+
   return stop;
 }