From 1fe2833b6dd03602ba86aa334e81466ea9abe66a Mon Sep 17 00:00:00 2001 From: Pedro Alves Date: Wed, 9 Jul 2014 17:52:58 +0100 Subject: Fix "attach" command vs user input race On async targets, a synchronous attach is done like this: #1 - target_attach is called (PTRACE_ATTACH is issued) #2 - a continuation is installed #3 - we go back to the event loop #4 - target reports stop (SIGSTOP), event loop wakes up, and attach continuation is called #5 - among other things, the continuation calls target_terminal_inferior, which removes stdin from the event loop Note that in #3, GDB is still processing user input. If the user is fast enough, e.g., with something like: echo -e "attach PID\nset xxx=1" | gdb ... then the "set" command is processed before the attach completes. We get worse behavior even, if input is a tty and therefore readline/editing is enabled, with e.g.,: (gdb) attach PID\nset xxx=1 we then crash readline/gdb, with: Attaching to program: attach-wait-input, process 14537 readline: readline_callback_read_char() called with no handler! Aborted $ Fix this by calling target_terminal_inferior before #3 above. The test covers both scenarios by running with editing/readline forced to both on and off. gdb/ 2014-07-09 Pedro Alves * infcmd.c (attach_command_post_wait): Don't call target_terminal_inferior here. (attach_command): Call it here instead. gdb/testsuite/ 2014-07-09 Pedro Alves * gdb.base/attach-wait-input.exp: New file. * gdb.base/attach-wait-input.c: New file. --- gdb/infcmd.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) (limited to 'gdb/infcmd.c') diff --git a/gdb/infcmd.c b/gdb/infcmd.c index df4fd40..a712b6f 100644 --- a/gdb/infcmd.c +++ b/gdb/infcmd.c @@ -2381,9 +2381,6 @@ attach_command_post_wait (char *args, int from_tty, int async_exec) post_create_inferior (¤t_target, from_tty); - /* Install inferior's terminal modes. */ - target_terminal_inferior (); - if (async_exec) { /* The user requested an `attach&', so be sure to leave threads @@ -2499,6 +2496,22 @@ attach_command (char *args, int from_tty) based on what modes we are starting it with. */ target_terminal_init (); + /* Install inferior's terminal modes. This may look like a no-op, + as we've just saved them above, however, this does more than + restore terminal settings: + + - installs a SIGINT handler that forwards SIGINT to the inferior. + Otherwise a Ctrl-C pressed just while waiting for the initial + stop would end up as a spurious Quit. + + - removes stdin from the event loop, which we need if attaching + in the foreground, otherwise on targets that report an initial + stop on attach (which are most) we'd process input/commands + while we're in the event loop waiting for that stop. That is, + before the attach continuation runs and the command is really + finished. */ + target_terminal_inferior (); + /* Set up execution context to know that we should return from wait_for_inferior as soon as the target reports a stop. */ init_wait_for_inferior (); -- cgit v1.1