[C++] Always use setjmp/longjmp for exceptions
Commit Message
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:
2015-11-03 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.
---
gdb/common/common-exceptions.c | 10 +++++-----
gdb/common/common-exceptions.h | 39 ++++++++++++++++++++++++++++-----------
2 files changed, 33 insertions(+), 16 deletions(-)
Comments
On 11/03/2015 04:48 PM, Pedro Alves wrote:
> 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:
> 2015-11-03 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.
This is now pushed.
Thanks,
Pedro Alves
@@ -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;
@@ -116,12 +116,32 @@ struct gdb_exception
const char *message;
};
+/* The different exception mechanisms that TRY/CATCH can map to. */
+
+/* Make GDB exceptions use setjmp/longjmp behind the scenes. This is
+ the only mode supported when GDB is built as a C program. */
+#define GDB_XCPT_SJMP 1
+
+/* Make GDB exceptions use try/catch behind the scenes. Can't be made
+ the default until we stop throwing exceptions from signal
+ handlers. */
+#define GDB_XCPT_TRY 2
+
+/* Specify this mode to build with TRY/CATCH mapped directly to raw
+ try/catch. GDB won't work correctly, but building that way catches
+ code tryin to break/continue out of the try block, along with
+ spurious code between the TRY and the CATCH block. */
+#define GDB_XCPT_RAW_TRY 3
+
+/* Always use setjmp/longmp, even in C++ mode. */
+#define GDB_XCPT GDB_XCPT_SJMP
+
/* Functions to drive the exceptions state machine. Though declared
here by necessity, these functions should be considered internal to
the exceptions subsystem and not used other than via the TRY/CATCH
macros defined below. */
-#ifndef __cplusplus
+#if GDB_XCPT == GDB_XCPT_SJMP
extern SIGJMP_BUF *exceptions_state_mc_init (void);
extern int exceptions_state_mc_action_iter (void);
extern int exceptions_state_mc_action_iter_1 (void);
@@ -157,7 +177,7 @@ extern void exception_rethrow (void);
*/
-#ifndef __cplusplus
+#if GDB_XCPT == GDB_XCPT_SJMP
#define TRY \
{ \
@@ -176,7 +196,9 @@ extern void exception_rethrow (void);
#define END_CATCH \
}
-#else
+#endif /* GDB_XCPT_SJMP */
+
+#if GDB_XCPT == GDB_XCPT_TRY || GDB_XCPT == GDB_XCPT_RAW_TRY
/* Prevent error/quit during TRY from calling cleanups established
prior to here. This pops out the scope in either case of normal
@@ -195,13 +217,7 @@ struct exception_try_scope
void *saved_state;
};
-/* Define this to build with TRY/CATCH mapped directly to raw
- try/catch. GDB won't work correctly, but building that way catches
- code tryin to break/continue out of the try block, along with
- spurious code between the TRY and the CATCH block. */
-//#define USE_RAW_CXX_TRY
-
-#ifndef USE_RAW_CXX_TRY
+#if GDB_XCPT == GDB_XCPT_TRY
/* We still need to wrap TRY/CATCH in C++ so that cleanups and C++
exceptions can coexist. The TRY blocked is wrapped in a
@@ -224,6 +240,7 @@ struct exception_try_scope
{ \
exception_rethrow (); \
}
+
#else
#define TRY try
@@ -249,7 +266,7 @@ struct gdb_exception_RETURN_MASK_QUIT : public gdb_exception_RETURN_MASK_ALL
{
};
-#endif
+#endif /* GDB_XCPT_TRY || GDB_XCPT_RAW_TRY */
/* *INDENT-ON* */