[C++] Always use setjmp/longjmp for exceptions

We currently throw exceptions from signal handlers (e.g., for
Quit/ctrl-c).  But throwing C++ exceptions from signal handlers is
undefined.  (That doesn't restore signal masks, like siglongjmp does,
and, because asynchronous signals can arrive at any instruction, we'd
have to build _everything_ with -fasync-unwind-tables to make it
reliable.)  It happens to work on x86_64 GNU/Linux at least, but it's
likely broken on other ports.

Until we stop throwing from signal handlers, use setjmp/longjmp based
exceptions in C++ mode as well.

gdb/ChangeLog:
2015-11-17  Pedro Alves  <palves@redhat.com>

	* common/common-exceptions.h (GDB_XCPT_SJMP, GDB_XCPT_TRY)
	(GDB_XCPT_RAW_TRY, GDB_XCPT): Define.
	Replace __cplusplus checks with GDB_XCPT checks throughout.
	* common/common-exceptions.c: Replace __cplusplus checks with
	GDB_XCPT checks throughout.

1 files changed, 5 insertions, 5 deletions

diff --git a/gdb/common/common-exceptions.c b/gdb/common/common-exceptions.c
index ce476a2..231bab5 100644
--- a/gdb/common/common-exceptions.c
+++ b/gdb/common/common-exceptions.c
@@ -22,7 +22,7 @@
 
 const struct gdb_exception exception_none = { (enum return_reason) 0, GDB_NO_ERROR, NULL };
 
-#ifndef __cplusplus
+#if GDB_XCPT == GDB_XCPT_SJMP
 
 /* Possible catcher states.  */
 enum catcher_state {
@@ -213,7 +213,7 @@ exceptions_state_mc_action_iter_1 (void)
   return exceptions_state_mc (CATCH_ITER_1);
 }
 
-#else /* !__cplusplus */
+#else /* !GDB_XCPT_SJMP */
 
 /* How many nested TRY blocks we have.  See exception_messages and
    throw_it.  */
@@ -261,7 +261,7 @@ gdb_exception_sliced_copy (struct gdb_exception *to, const struct gdb_exception
   *to = *from;
 }
 
-#endif /* !__cplusplus */
+#endif /* !GDB_XCPT_SJMP */
 
 /* Return EXCEPTION to the nearest containing catch_errors().  */
 
@@ -272,7 +272,7 @@ throw_exception (struct gdb_exception exception)
 
   do_cleanups (all_cleanups ());
 
-#ifndef __cplusplus
+#if GDB_XCPT == GDB_XCPT_SJMP
   /* Jump to the containing catch_errors() call, communicating REASON
      to that call via setjmp's return value.  Note that REASON can't
      be zero, by definition in defs.h.  */
@@ -320,7 +320,7 @@ throw_it (enum return_reason reason, enum errors error, const char *fmt,
 {
   struct gdb_exception e;
   char *new_message;
-#ifndef __cplusplus
+#if GDB_XCPT == GDB_XCPT_SJMP
   int depth = catcher_list_size ();
 #else
   int depth = try_scope_depth;