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[RFC master/7.12.1] Don't propagate C++ exceptions across readline using SjLj on SjLj-based exception unwinding
- From: Yao Qi <qiyaoltc at gmail dot com>
- To: gdb-patches at sourceware dot org
- Date: Mon, 19 Dec 2016 14:42:17 +0000
- Subject: [RFC master/7.12.1] Don't propagate C++ exceptions across readline using SjLj on SjLj-based exception unwinding
- Authentication-results: sourceware.org; auth=none
Nowadays, we propagate C++ exceptions across readline using
setjmp/longjmp 89525768cd086a0798a504c81fdf7ebcd4c904e1
(Propagate GDB/C++ exceptions across readline using sj/lj-based TRY/CATCH)
because DWARF-based unwinding can't cross C function (see
details from the commit above). However, SjLj-based exception
unwinding doesn't have such issue.
What is more, looks longjmp may break the SjLj-based exception
handling, because _Unwind_SjLj_Unregister, which is put the exit
of function, is not executed due to longjmp.
(gdb) [New Thread 2936.0xb80]
kill
Thread 1 received signal SIGSEGV, Segmentation fault.
0x03ff662b in ?? ()
top?bt 15
#0 0x03ff662b in ?? ()
#1 0x00526b92 in stdin_event_handler (error=0, client_data=0x172ed8)
at ../../binutils-gdb/gdb/event-top.c:555
#2 0x00525a94 in handle_file_event (ready_mask=<optimized out>,
file_ptr=0x3ff5cb8) at ../../binutils-gdb/gdb/event-loop.c:733
#3 gdb_wait_for_event (block=block@entry=1)
at ../../binutils-gdb/gdb/event-loop.c:884
#4 0x00525bfb in gdb_do_one_event ()
at ../../binutils-gdb/gdb/event-loop.c:347
#5 0x00525ce5 in start_event_loop ()
at ../../binutils-gdb/gdb/event-loop.c:371
#6 0x0051fada in captured_command_loop (data=0x0)
at ../../binutils-gdb/gdb/main.c:324
#7 0x0051cf5d in catch_errors (
func=func@entry=0x51fab0 <captured_command_loop(void*)>,
func_args=func_args@entry=0x0,
errstring=errstring@entry=0x7922bf <VEC_interp_factory_p_quick_push(VEC_inte rp_factory_p*, interp_factory*, char const*, unsigned int)::__PRETTY_FUNCTION__+351> "", mask=mask@entry=RETURN_MASK_ALL)
at ../../binutils-gdb/gdb/exceptions.c:236
#8 0x00520f0c in captured_main (data=0x328feb4)
at ../../binutils-gdb/gdb/main.c:1149
#9 gdb_main (args=args@entry=0x328feb4) at ../../binutils-gdb/gdb/main.c:1159
#10 0x0071e400 in main (argc=1, argv=0x171220)
at ../../binutils-gdb/gdb/gdb.c:32
I dig into libcc/unwind-sjlj.c and gcc/except.c, but I still
don't find much clue. This patch fixes this issue by not propagating
the exception via setjmp/longjmp if __USING_SJLJ_EXCEPTIONS__.
gdb:
2016-12-19 Yao Qi <yao.qi@linaro.org>
PR gdb/20977
* event-top.c (gdb_rl_callback_read_char_wrapper): New function.
(gdb_rl_callback_read_char_wrapper): Call
gdb_rl_callback_read_char_wrapper.
(gdb_rl_callback_handler_1): New function.
(gdb_rl_callback_handler): Call gdb_rl_callback_handler_1.
---
gdb/event-top.c | 34 ++++++++++++++++++++++++++++------
1 file changed, 28 insertions(+), 6 deletions(-)
diff --git a/gdb/event-top.c b/gdb/event-top.c
index acf8474..db3a18f 100644
--- a/gdb/event-top.c
+++ b/gdb/event-top.c
@@ -121,6 +121,14 @@ static struct async_signal_handler *async_sigterm_token;
void (*after_char_processing_hook) (void);
+static void
+gdb_rl_callback_read_char_wrapper (void)
+{
+ rl_callback_read_char ();
+ if (after_char_processing_hook)
+ (*after_char_processing_hook) ();
+}
+
/* Wrapper function for calling into the readline library. This takes
care of a couple things:
@@ -136,7 +144,8 @@ void (*after_char_processing_hook) (void);
Any exception that tries to propagate through such code will fail
and the result is a call to std::terminate. While some ABIs, such
as x86-64, require all code to be built with exception tables,
- others don't.
+ others don't. However SJLJ-based unwinding doesn't have such
+ problem.
This is a problem when GDB calls some non-EH-aware C library code,
that calls into GDB again through a callback, and that GDB callback
@@ -162,6 +171,9 @@ void (*after_char_processing_hook) (void);
static void
gdb_rl_callback_read_char_wrapper (gdb_client_data client_data)
{
+#ifdef __USING_SJLJ_EXCEPTIONS__
+ gdb_rl_callback_read_char_wrapper();
+#else
struct gdb_exception gdb_expt = exception_none;
/* C++ exceptions can't normally be thrown across readline (unless
@@ -170,9 +182,7 @@ gdb_rl_callback_read_char_wrapper (gdb_client_data client_data)
TRY/CATCH, and rethrow the GDB exception once back in GDB. */
TRY_SJLJ
{
- rl_callback_read_char ();
- if (after_char_processing_hook)
- (*after_char_processing_hook) ();
+ gdb_rl_callback_read_char_wrapper();
}
CATCH_SJLJ (ex, RETURN_MASK_ALL)
{
@@ -183,6 +193,15 @@ gdb_rl_callback_read_char_wrapper (gdb_client_data client_data)
/* Rethrow using the normal EH mechanism. */
if (gdb_expt.reason < 0)
throw_exception (gdb_expt);
+#endif
+}
+
+static void
+gdb_rl_callback_handler_1 (char *rl)
+{
+ struct ui *ui = current_ui;
+
+ ui->input_handler (rl);
}
/* GDB's readline callback handler. Calls the current INPUT_HANDLER,
@@ -192,12 +211,14 @@ gdb_rl_callback_read_char_wrapper (gdb_client_data client_data)
static void
gdb_rl_callback_handler (char *rl)
{
+#ifdef __USING_SJLJ_EXCEPTIONS__
+ gdb_rl_callback_handler_1 (rl);
+#else
struct gdb_exception gdb_rl_expt = exception_none;
- struct ui *ui = current_ui;
TRY
{
- ui->input_handler (rl);
+ gdb_rl_callback_handler_1 (rl);
}
CATCH (ex, RETURN_MASK_ALL)
{
@@ -214,6 +235,7 @@ gdb_rl_callback_handler (char *rl)
dtors are NOT run automatically. */
if (gdb_rl_expt.reason < 0)
throw_exception_sjlj (gdb_rl_expt);
+#endif
}
/* Change the function to be invoked every time there is a character
--
1.9.1