[PATCH v4 8/8] Forced quit cases handled by resetting sync_quit_force_run

Kevin Buettner via Gdb-patches
2023-01-12T01:58:14Z

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
---
gdb/linux-fork.c | 13 +++++++++++++
gdb/tui/tui-io.c | 9 +++++++++
2 files changed, 22 insertions(+)

diff --git a/gdb/linux-fork.c b/gdb/linux-fork.c
index 61545b859ea..fc2f00d0766 100644
--- a/gdb/linux-fork.c
+++ b/gdb/linux-fork.c
@@ -430,6 +430,19 @@ 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. */
+ sync_quit_force_run = 1;
+ set_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 2f39e34df2f..ac3c7296499 100644
--- a/gdb/tui/tui-io.c
+++ b/gdb/tui/tui-io.c
@@ -1275,6 +1275,15 @@ 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. */
+ sync_quit_force_run = 1;
+ set_quit_flag ();
+ return 0;
+ }
catch (const gdb_exception &ex)
{
/* Just in case, don't ever let an exception escape to readline.
--
2.34.3