From d3d4baedb6d247c6372678edd15195a1a93c2c6c Mon Sep 17 00:00:00 2001 From: Pedro Alves Date: Thu, 23 Oct 2014 17:13:35 +0100 Subject: PR python/17372 - Python hangs when displaying help() This is more of a readline/terminal issue than a Python one. PR17372 is a regression in 7.8 caused by the fix for PR17072: commit 0017922d0292d8c374584f6100874580659c9973 Author: Pedro Alves Date: Mon Jul 14 19:55:32 2014 +0100 Background execution + pagination aborts readline/gdb gdb_readline_wrapper_line removes the handler after a line is processed. Usually, we'll end up re-displaying the prompt, and that reinstalls the handler. But if the output is coming out of handling a stop event, we don't re-display the prompt, and nothing restores the handler. So the next input wakes up the event loop and calls into readline, which aborts. ... gdb/ 2014-07-14 Pedro Alves PR gdb/17072 * top.c (gdb_readline_wrapper_line): Tweak comment. (gdb_readline_wrapper_cleanup): If readline is enabled, reinstall the input handler callback. The problem is that installing the input handler callback also preps the terminal, putting it in raw mode and with echo disabled, which is bad if we're going to call a command that assumes cooked/canonical mode, and echo enabled, like in the case of the PR, Python's interactive shell. Another example I came up with that doesn't depend on Python is starting a subshell with "(gdb) shell /bin/sh" from a multi-line command. Tests covering both these examples are added. The fix is to revert the original fix for PR gdb/17072, and instead restore the callback handler after processing an asynchronous target event. Furthermore, calling rl_callback_handler_install when we already have some input in readline's line buffer discards that input, which is obviously a bad thing to do while the user is typing. No specific test is added for that, because I first tried calling it even if the callback handler was still installed and that resulted in hundreds of failures in the testsuite. gdb/ 2014-10-29 Pedro Alves PR python/17372 * event-top.c (change_line_handler): Call gdb_rl_callback_handler_remove instead of rl_callback_handler_remove. (callback_handler_installed): New global. (gdb_rl_callback_handler_remove, gdb_rl_callback_handler_install) (gdb_rl_callback_handler_reinstall): New functions. (display_gdb_prompt): Call gdb_rl_callback_handler_remove and gdb_rl_callback_handler_install instead of rl_callback_handler_remove and rl_callback_handler_install. (gdb_disable_readline): Call gdb_rl_callback_handler_remove instead of rl_callback_handler_remove. * event-top.h (gdb_rl_callback_handler_remove) (gdb_rl_callback_handler_install) (gdb_rl_callback_handler_reinstall): New declarations. * infrun.c (reinstall_readline_callback_handler_cleanup): New cleanup function. (fetch_inferior_event): Install it. * top.c (gdb_readline_wrapper_line) Call gdb_rl_callback_handler_remove instead of rl_callback_handler_remove. (gdb_readline_wrapper_cleanup): Don't call rl_callback_handler_install. gdb/testsuite/ 2014-10-29 Pedro Alves PR python/17372 * gdb.python/python.exp: Test a multi-line command that spawns interactive Python. * gdb.base/multi-line-starts-subshell.exp: New file. --- gdb/top.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) (limited to 'gdb/top.c') diff --git a/gdb/top.c b/gdb/top.c index 5a947d718c8..83d858adcfc 100644 --- a/gdb/top.c +++ b/gdb/top.c @@ -763,9 +763,14 @@ gdb_readline_wrapper_line (char *line) /* Prevent parts of the prompt from being redisplayed if annotations are enabled, and readline's state getting out of sync. We'll - restore it in gdb_readline_wrapper_cleanup. */ + reinstall the callback handler, which puts the terminal in raw + mode (or in readline lingo, in prepped state), when we're next + ready to process user input, either in display_gdb_prompt, or if + we're handling an asynchronous target event and running in the + background, just before returning to the event loop to process + further input (or more target events). */ if (async_command_editing_p) - rl_callback_handler_remove (); + gdb_rl_callback_handler_remove (); } struct gdb_readline_wrapper_cleanup @@ -787,10 +792,12 @@ gdb_readline_wrapper_cleanup (void *arg) gdb_assert (input_handler == gdb_readline_wrapper_line); input_handler = cleanup->handler_orig; - /* Reinstall INPUT_HANDLER in readline, without displaying a - prompt. */ - if (async_command_editing_p) - rl_callback_handler_install (NULL, input_handler); + /* Don't restore our input handler in readline yet. That would make + readline prep the terminal (putting it in raw mode), while the + line we just read may trigger execution of a command that expects + the terminal in the default cooked/canonical mode, such as e.g., + running Python's interactive online help utility. See + gdb_readline_wrapper_line for when we'll reinstall it. */ gdb_readline_wrapper_result = NULL; gdb_readline_wrapper_done = 0; -- cgit v1.2.1