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From: Tom de Vries <vries@sourceware.org> To: gdb-cvs@sourceware.org Subject: [binutils-gdb] [gdb] Handle pending ^C after rl_callback_read_char Date: Fri, 16 Sep 2022 13:53:51 +0000 (GMT) [thread overview] Message-ID: <20220916135351.A5D213853829@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=faf01aee1d03aef5b6f95fd0db358bf5e70578f9 commit faf01aee1d03aef5b6f95fd0db358bf5e70578f9 Author: Tom de Vries <tdevries@suse.de> Date: Fri Sep 16 15:53:47 2022 +0200 [gdb] Handle pending ^C after rl_callback_read_char In completion tests in various test-cases, we've been running into these "clearing input line" timeouts: ... (gdb) $cmd^GPASS: gdb.gdb/unittest.exp: tab complete "$cmd" FAIL: gdb.gdb/unittest.exp: tab complete "$cmd" (clearing input line) (timeout) ... where $cmd == "maintenance selftest name_that_does_not_exist". AFAIU, the following scenario happens: - expect sends "$cmd\t" - gdb detects the stdin event, and calls rl_callback_read_char until it comes to handle \t - readline interprets the \t as completion, tries to complete, fails to do so, outputs a bell (^G) - expect sees the bell, and proceeds to send ^C - readline is still in the call to rl_callback_read_char, and stores the signal in _rl_caught_signal - readline returns from the call to rl_callback_read_char, without having handled _rl_caught_signal - gdb goes to wait for the next event - expect times out waiting for "Quit", the expected reaction for ^C Fix this by handling pending signals after each call to rl_callback_read_char. The fix is only available for readline 8.x, if --with-system-readline provides an older version, then the fix is disabled due to missing function rl_check_signals. Tested on x86_64-linux. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27813 Diff: --- gdb/event-top.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/gdb/event-top.c b/gdb/event-top.c index 290c3d87744..00adbe8fb4f 100644 --- a/gdb/event-top.c +++ b/gdb/event-top.c @@ -186,6 +186,22 @@ gdb_rl_callback_read_char_wrapper_noexcept () noexcept TRY_SJLJ { rl_callback_read_char (); +#if RL_VERSION_MAJOR >= 8 + /* It can happen that readline (while in rl_callback_read_char) + received a signal, but didn't handle it yet. Make sure it's handled + now. If we don't do that we run into two related problems: + - we have to wait for another event triggering + rl_callback_read_char before the signal is handled + - there's no guarantee that the signal will be processed before the + event. */ + while (rl_pending_signal () != 0) + /* Do this in a while loop, in case rl_check_signals also leaves a + pending signal. I'm not sure if that's possible, but it seems + better to handle the scenario than to assert. */ + rl_check_signals (); +#else + /* Unfortunately, rl_check_signals is not available. */ +#endif if (after_char_processing_hook) (*after_char_processing_hook) (); }
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