Re: [pushed+7.8] Re: [PATCH] Fix "attach" command vs user input race [Re: Regression for attach from stdin [Re: [pushed] Re: [PATCH v6 0/2] enable target-async by default]]

Doug Evans
2014-07-29T21:48:44Z

On Wed, Jul 9, 2014 at 10:09 AM, Pedro Alves <palves@redhat.com> wrote:
> On 07/09/2014 05:37 PM, Doug Evans wrote:
>
>> spurious change
>
> Fixed.
>
>> I like this a lot better. Thanks.
>> The patch is ok with me, modulo removing the spurious change.
>
> Here's what I pushed to both master and gdb-7.8-branch.
>
> Thanks.
>
> -------------
> From 1fe2833b6dd03602ba86aa334e81466ea9abe66a Mon Sep 17 00:00:00 2001
> From: Pedro Alves <palves@redhat.com>
> Date: Wed, 9 Jul 2014 17:52:58 +0100
> Subject: [PATCH] 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 <palves@redhat.com>
>
> * 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 <palves@redhat.com>
>
> * gdb.base/attach-wait-input.exp: New file.
> * gdb.base/attach-wait-input.c: New file.

Hi.

Is this TODO still needed after this patch?

infcmd.c:

/*
* TODO:
* Should save/restore the tty state since it might be that the
* program to be debugged was started on this tty and it wants
* the tty in some state other than what we want. If it's running
* on another terminal or without a terminal, then saving and
* restoring the tty state is a harmless no-op.
* This only needs to be done if we are attaching to a process.
*/