[PATCH v5 8/8] Forced quit cases handled by resetting sync_quit_force_run

Kevin Buettner via Gdb-patches
2023-02-22T23:48:05Z

During my audit of the use of gdb_exception with regard to QUIT
processing, I found a try/catch in the scoped_switch_fork_info
destructor.

Static analysis found this call path from the destructor to
maybe_quit():

scoped_switch_fork_info::~scoped_switch_fork_info()
-> remove_breakpoints()
-> remove_breakpoint(bp_location*)
-> remove_breakpoint_1(bp_location*, remove_bp_reason)
-> memory_validate_breakpoint(gdbarch*, bp_target_info*)
-> target_read_memory(unsigned long, unsigned char*, long)
-> target_read(target_ops*, target_object, char const*, unsigned char*, unsigned long, long)
-> maybe_quit()

Since it's not safe to do a 'throw' from a destructor, we simply
call set_quit_flag and, for gdb_exception_forced_quit, also
set sync_quit_force_run. This will cause the appropriate
exception to be rethrown at the next QUIT check.

Another case is the try / catch in tui_getc() in tui-io.c. The
existing catch swallows the exception. I've added a catch for
'gdb_exception_forced_quit', which also swallows the exception,
but also sets sync_quit_force_run and calls set_quit_flag in
order to restart forced quit processing at the next QUIT check.
This is required because it isn't safe to throw into/through
readline.

Thanks to Pedro Alves for suggesting this idea.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=26761
Tested-by: Tom de Vries <tdevries@suse.de>
---
gdb/linux-fork.c | 12 ++++++++++++
gdb/tui/tui-io.c | 8 ++++++++
gdb/tui/tui.c | 7 +++++++
3 files changed, 27 insertions(+)

diff --git a/gdb/linux-fork.c b/gdb/linux-fork.c
index 61545b859ea..a6e74c0cb52 100644
--- a/gdb/linux-fork.c
+++ b/gdb/linux-fork.c
@@ -430,6 +430,18 @@ class scoped_switch_fork_info
fork_load_infrun_state (m_oldfp);
insert_breakpoints ();
}
+ catch (const gdb_exception_quit &ex)
+ {
+ /* We can't throw from a destructor, so re-set the quit flag
+ for later QUIT checking. */
+ set_quit_flag ();
+ }
+ catch (const gdb_exception_forced_quit &ex)
+ {
+ /* Like above, but (eventually) cause GDB to terminate by
+ setting sync_quit_force_run. */
+ set_force_quit_flag ();
+ }
catch (const gdb_exception &ex)
{
warning (_("Couldn't restore checkpoint state in %s: %s"),
diff --git a/gdb/tui/tui-io.c b/gdb/tui/tui-io.c
index a17cf38a1f2..7752701378e 100644
--- a/gdb/tui/tui-io.c
+++ b/gdb/tui/tui-io.c
@@ -1271,6 +1271,14 @@ tui_getc (FILE *fp)
{
return tui_getc_1 (fp);
}
+ catch (const gdb_exception_forced_quit &ex)
+ {
+ /* As noted below, it's not safe to let an exception escape
+ to newline, so, for this case, reset the quit flag for
+ later QUIT checking. */
+ set_force_quit_flag ();
+ return 0;
+ }
catch (const gdb_exception &ex)
{
/* Just in case, don't ever let an exception escape to readline.
diff --git a/gdb/tui/tui.c b/gdb/tui/tui.c
index cdae9ffe02b..3604194a760 100644
--- a/gdb/tui/tui.c
+++ b/gdb/tui/tui.c
@@ -122,6 +122,13 @@ tui_rl_switch_mode (int notused1, int notused2)
tui_enable ();
}
}
+ catch (const gdb_exception_forced_quit &ex)
+ {
+ /* Ideally, we'd do a 'throw' here, but as noted above, we can't
+ do that, so, instead, we'll set the necessary flags so that
+ a later QUIT check will restart the forced quit. */
+ set_force_quit_flag ();
+ }
catch (const gdb_exception &ex)
{
exception_print (gdb_stderr, ex);
--
2.34.3