[RFA] exceptions.h: Fix definition of TRY_CATCH

Corinna Vinschen
2005-03-09T16:48:26Z

Hi,

this patch

http://sourceware.org/ml/gdb/2005-01/msg00064.html

unfortunately breaks Cygwin.

The reason is the way how TRY_CATCH is defined as a macro:

#define TRY_CATCH(EXCEPTION,MASK) \
for (EXCEPTIONS_SIGSETJMP \
(*exceptions_state_mc_init (uiout, &(EXCEPTION), (MASK))); \
exceptions_state_mc_action_iter () ; ) \
while (exceptions_state_mc_action_iter_1 ())

it calls EXCEPTIONS_SIGSETJMP (aka sigsetjmp on systems supporting it),
without bothering how sigsetjmp is defined on the host system.

Cygwin's (as well as RTEMS') sigsetjmp is defined in newlib's machine/setjmp.h
as a macro, too:

#define sigsetjmp(env, savemask) ((env)[_SAVEMASK] = savemask,\
sigprocmask (SIG_SETMASK, 0, (sigset_t *) ((env) + _SIGMASK)),\
setjmp (env))

If you inspect it, you'll see that the first parameter `env' is evaluated
three times. Since the first parameter is a call to the function
exceptions_state_mc_init(), the result is that three new catcher structures
are created. But only one of them, the last one which has been created,
is correctly iniitialized by the call to exceptions_state_mc_action_iter().
I guess you see what will happen at one point. A non-initialized catcher
is current when the function exceptions_state_mc_action_iter_1() is called
==> internal_error.

Note that this is *not* a flaw in newlib or Cygwin. It's perfectly fine
that setjmp and sigsetjmp are defined as macros as above, see
http://www.opengroup.org/onlinepubs/009695399/functions/setjmp.html and
http://www.opengroup.org/onlinepubs/009695399/functions/sigsetjmp.html,
so the usual macro expansion restrictions apply.

Conclusion: The actual problem is that the sigjmp_buf is created in a
function call which is the first parameter to sigsetjmp.

Solution: Don't do it. :-)

A patch is below. Tested on Cygwin and Linux.

Ok to check in?

Corinna

* exceptions.h (TRY_CATCH): Define setjmp/sigsetjmp macro save.

Index: exceptions.h
===================================================================
RCS file: /cvs/src/src/gdb/exceptions.h,v
retrieving revision 1.11
diff -u -p -r1.11 exceptions.h
--- exceptions.h 8 Feb 2005 23:44:06 -0000 1.11
+++ exceptions.h 9 Mar 2005 15:14:41 -0000
@@ -115,10 +115,13 @@ int exceptions_state_mc_action_iter_1 (v
*/

#define TRY_CATCH(EXCEPTION,MASK) \
- for (EXCEPTIONS_SIGSETJMP \
- (*exceptions_state_mc_init (uiout, &(EXCEPTION), (MASK))); \
- exceptions_state_mc_action_iter (); ) \
- while (exceptions_state_mc_action_iter_1 ())
+ { \
+ EXCEPTIONS_SIGJMP_BUF *buf = \
+ exceptions_state_mc_init (uiout, &(EXCEPTION), (MASK)); \
+ EXCEPTIONS_SIGSETJMP (*buf); \
+ } \
+ while (exceptions_state_mc_action_iter ()) \
+ while (exceptions_state_mc_action_iter_1 ())

/* *INDENT-ON* */

--
Corinna Vinschen
Cygwin Project Co-Leader
Red Hat, Inc.