[PATCH v4 7/8] QUIT processing w/ explicit throw for gdb_exception_forced_quit

Kevin Buettner via Gdb-patches
2023-01-12T01:58:30Z

This commit contains changes which have an explicit throw for
gdb_exception_forced_quit, or, in a couple of cases for gdb_exception,
but with a throw following a check to see if 'reason' is
RETURN_FORCED_QUIT.

Most of these are straightforward - it made sense to continue to allow
an existing catch of gdb_exception to also catch gdb_exception_quit;
in these cases, a catch/throw for gdb_exception_forced_quit was added.

There are two cases, however, which deserve a more detailed
explanation.

1) remote_fileio_request in gdb/remote-fileio.c:

The try block calls do_remote_fileio_request which can (in turn)
call one of the functions in remote_fio_func_map[]. Taking the
first one, remote_fileio_func_open(), we have the following call
path to maybe_quit():

remote_fileio_func_open(remote_target*, char*)
-> target_read_memory(unsigned long, unsigned char*, long)
-> target_read(target_ops*, target_object, char const*, unsigned char*, unsigned long, long)
-> maybe_quit()

Since there is a path to maybe_quit(), we must ensure that the
catch block is not permitted to swallow a QUIT representing a
SIGTERM.

However, for this case, we must take care not to change the way that
Ctrl-C / SIGINT is handled; we want to send a suitable EINTR reply to
the remote target should that happen. That being the case, I added a
catch/throw for gdb_exception_forced_quit. I also did a bit of
rewriting here, adding a catch for gdb_exception_quit in favor of
checking the 'reason' code in the catch block for gdb_exception.

2) mi_execute_command in gdb/mi/mi-main.c:

The try block calls captured_mi_execute_command(); there exists
a call path to maybe_quit():

captured_mi_execute_command(ui_out*, mi_parse*)
-> mi_cmd_execute(mi_parse*)
-> get_current_frame()
-> get_prev_frame_always_1(frame_info*)
-> frame_register_unwind_location(frame_info*, int, int*, lval_type*, unsigned long*, int*)
-> frame_register_unwind(frame_info*, int, int*, int*, lval_type*, unsigned long*, int*, unsigned char*)
-> value_entirely_available(value*)
-> value_fetch_lazy(value*)
-> value_fetch_lazy_memory(value*)
-> read_value_memory(value*, long, int, unsigned long, unsigned char*, unsigned long)
-> maybe_quit()

That being the case, we can't allow the exception handler (catch block)
to swallow a gdb_exception_quit for SIGTERM. However, it does seem
reasonable to output the exception via the mi interface so that some
suitable message regarding SIGTERM might be printed; therefore, I
check the exception's 'reason' field for RETURN_FORCED_QUIT and
do a throw for this case.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=26761
---
gdb/event-top.c | 2 ++
gdb/mi/mi-main.c | 4 ++++
gdb/remote-fileio.c | 15 ++++++++++-----
gdb/tui/tui.c | 4 ++++
4 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/gdb/event-top.c b/gdb/event-top.c
index 4a46e1b9346..9d34e574653 100644
--- a/gdb/event-top.c
+++ b/gdb/event-top.c
@@ -1281,6 +1281,8 @@ async_disconnect (gdb_client_data arg)
gdb_puts ("Could not kill the program being debugged",
gdb_stderr);
exception_print (gdb_stderr, exception);
+ if (exception.reason == RETURN_FORCED_QUIT)
+ throw;
}

for (inferior *inf : all_inferiors ())
diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
index e0cade2edc3..d7ca7843d6f 100644
--- a/gdb/mi/mi-main.c
+++ b/gdb/mi/mi-main.c
@@ -1952,6 +1952,10 @@ mi_execute_command (const char *cmd, int from_tty)
somewhere. */
mi_print_exception (command->token, result);
mi_out_rewind (current_uiout);
+
+ /* Throw to a higher level catch for SIGTERM sent to GDB. */
+ if (result.reason == RETURN_FORCED_QUIT)
+ throw;
}

bpstat_do_actions ();
diff --git a/gdb/remote-fileio.c b/gdb/remote-fileio.c
index 3ff2a65b0ec..c804b0b2098 100644
--- a/gdb/remote-fileio.c
+++ b/gdb/remote-fileio.c
@@ -1191,12 +1191,17 @@ remote_fileio_request (remote_target *remote, char *buf, int ctrlc_pending_p)
{
do_remote_fileio_request (remote, buf);
}
- catch (const gdb_exception &ex)
+ catch (const gdb_exception_forced_quit &ex)
+ {
+ throw;
+ }
+ catch (const gdb_exception_quit &ex)
{
- if (ex.reason == RETURN_QUIT)
- remote_fileio_reply (remote, -1, FILEIO_EINTR);
- else
- remote_fileio_reply (remote, -1, FILEIO_EIO);
+ remote_fileio_reply (remote, -1, FILEIO_EINTR);
+ }
+ catch (const gdb_exception &ex)
+ {
+ remote_fileio_reply (remote, -1, FILEIO_EIO);
}
}

diff --git a/gdb/tui/tui.c b/gdb/tui/tui.c
index cdae9ffe02b..23b47ee163c 100644
--- a/gdb/tui/tui.c
+++ b/gdb/tui/tui.c
@@ -122,6 +122,10 @@ tui_rl_switch_mode (int notused1, int notused2)
tui_enable ();
}
}
+ catch (const gdb_exception_forced_quit &ex)
+ {
+ throw;
+ }
catch (const gdb_exception &ex)
{
exception_print (gdb_stderr, ex);
--
2.34.3