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Re: [PATCH] Per-inferior target_terminal state, fix PR gdb/13211, more


On 01/31/2018 09:27 AM, Christophe Lyon wrote:
> On 30 January 2018 at 16:37, Pedro Alves <palves@redhat.com> wrote:
>> On 12/04/2017 07:44 PM, Pedro Alves wrote:
>>> (This applies on top of:
>>>
>>>   [PATCH] linux-nat: Eliminate custom target_terminal_{inferior,ours}, stop using set_sigint_trap
>>>   https://sourceware.org/ml/gdb-patches/2017-11/msg00368.html
>>> )
>>>
>>> In my multi-target branch I ran into problems with GDB's terminal
>>> handling that exist in master as well, with multi-inferior debugging.
>>>
>>> This patch adds a testcase for said problems
>>> (gdb.multi/multi-term-settings.exp), fixes the problems, fixes PR
>>> gdb/13211 as well (and adds a testcase for that too,
>>> gdb.base/interrupt-daemon.exp).
>>>
>>> The basis of the problem I ran into is the following.  Consider a
>>> scenario where you have:
>>>
>>>  - inferior 1 - started with "attach", process is running on some
>>>    other terminal.
>>>
>>>  - inferior 2 - started with "run", process is sharing gdb's terminal.
>>>
>>> In this scenario, when you stop/resume both inferiors, you want GDB to
>>> save/restore the terminal settings of inferior 2, the one that is
>>> sharing GDB's terminal.  I.e., you want inferior 2 to "own" the
>>> terminal (in target_terminal::is_ours/target_terminal::is_inferior
>>> sense).
>>>
>>> Unfortunately, that's not what you get currently.  Because GDB doesn't
>>> know whether an attached inferior is actually sharing GDB's terminal,
>>> it tries to save/restore its settings anyway, ignoring errors.  In
>>> this case, this is pointless, because inferior 1 is running on a
>>> different terminal, but GDB doesn't know better.
>>>
>>> And then, because it is only possible to have the terminal settings of
>>> a single inferior be in effect at a time, or make one inferior/pgrp be
>>> the terminal's foreground pgrp (aka, only one inferior can "own" the
>>> terminal, ignoring fork children here), if GDB happens to try to
>>> restore the terminal settings of inferior 1 first, then GDB never
>>> restores the terminal settings of inferior 2.
>>>
>>> This patch fixes that and a few things more along the way:
>>>
>>>  - Moves enum target_terminal::terminal_state out of the
>>>    target_terminal class (it's currently private) and makes it a
>>>    scoped enum so that it can be easily used elsewhere.
>>>
>>>  - Replaces the inflow.c:terminal_is_ours boolean with a
>>>    target_terminal_state variable.  This allows distinguishing is_ours
>>>    and is_ours_for_output states.  This allows finally making
>>>    child_terminal_ours_1 do something with its "output_only"
>>>    parameter.
>>>
>>>  - Makes each inferior have its own copy of the
>>>    is_ours/is_ours_for_output/is_inferior state.
>>>
>>>  - Adds a way for GDB to tell whether the inferior is sharing GDB's
>>>    terminal.  Works best on Linux and Solaris; the fallback works just
>>>    as well as currently.
>>>
>>>  - With that, we can remove the inf->attach_flag tests from
>>>    child_terminal_inferior/child_terminal_ours.
>>>
>>>  - Currently target_ops.to_ours is responsible for both saving the
>>>    current inferior's terminal state, and restoring gdb's state.
>>>    Because each inferior has its own terminal state (possibly handled
>>>    by different targets in a multi-target world, even), we need to
>>>    split the inferior-saving part from the gdb-restoring part.  The
>>>    patch adds a new target_ops.to_save_inferior target method for
>>>    that.
>>>
>>>  - Adds a new target_terminal::save_inferior() function, so that
>>>    sequences like:
>>>
>>>      scoped_restore_terminal_state save_state;
>>>      target_terminal::ours_for_output ();
>>>
>>>    ... restore back inferiors that were
>>>    target_terminal_state::is_inferior before back to is_inferior, and
>>>    leaves inferiors that were is_ours alone.
>>>
>>>  - Along the way, this adds a default implementation of
>>>    target_pass_ctrlc to inflow.c (for inf-child.c), that handles
>>>    passing the Ctrl-C to a process running on GDB's terminal or to
>>>    some other process otherwise.
>>>
>>>  - Similarly, adds a new target default implementation of
>>>    target_interrupt, for the "interrupt" command.  The current
>>>    implementation of this hook in inf-ptrace.c kills the whole process
>>>    group, but that's incorrect/undesirable because we may not be
>>>    attached to all processes in the process group.  And also, it's
>>>    incorrect because inferior_process_group() doesn't really return
>>>    the inferior's real process group id if the inferior is not a
>>>    process group leader...  This is the cause of PR gdb/13211 [1],
>>>    which this patch fixes.  While at it, that target method's "ptid"
>>>    parameter is eliminated, because it's not really used.
>>>
>>>  - A new test is included that exercises and fixes PR gdb/13211, and
>>>    also fixes a GDB issue reported on stackoverflow that I ran into
>>>    while working on this [2].  The problem is similar to PR gdb/13211,
>>>    except that it also triggers with Ctrl-C.  When debugging a daemon
>>>    (i.e., a process that disconnects from the controlling terminal and
>>>    is not a process group leader, then Ctrl-C doesn't work, you just
>>>    can't interrupt the inferior at all, resulting in a hung debug
>>>    session.  The problem is that since the inferior is no longer
>>>    associated with gdb's session / controlling terminal, then trying
>>>    to put the inferior in the foreground fails.  And so Ctrl-C never
>>>    reaches the inferior directly.  pass_signal is only used when the
>>>    inferior is attached, but that is not the case here.  This is fixed
>>>    by the new child_pass_ctrlc.  Without the fix, the new
>>>    interrupt-daemon.exp testcase fails with timeout waiting for a
>>>    SIGINT that never arrives.
>>>
>>> [1] PR gdb/13211 - Async / Process group and interrupt not working
>>> https://sourceware.org/bugzilla/show_bug.cgi?id=13211
>>>
>>> [2] GDB not reacting Ctrl-C when after fork() and setsid()
>>> https://stackoverflow.com/questions/46101292/gdb-not-reacting-ctrl-c-when-after-fork-and-setsid
>>>
>>> Note this patch does _not_ fix:
>>>
>>>  - PR gdb/14559 - The 'interrupt' command does not work if sigwait is in use
>>>    https://sourceware.org/bugzilla/show_bug.cgi?id=14559
>>>
>>>  - PR gdb/9425 - When using "sigwait" GDB doesn't trap SIGINT. Ctrl+C terminates program when should break gdb.
>>>    https://sourceware.org/bugzilla/show_bug.cgi?id=9425
>>>
>>> The only way to fix that that I know of (without changing the kernel)
>>> is to make GDB put inferiors in a separate session (create a
>>> pseudo-tty master/slave pair, make the inferior run with the slave as
>>> its terminal, and have gdb pump output/input on the master end).  I
>>> have a follow up series that builds on top of this one that does that,
>>> but that's too invasive for 8.1, I think.  While this one fixes a
>>> couple bugs already, and I think having it in 8.1 would simplify
>>> backports for (a future) 8.1.1.
>>
>> I chickened out of putting this in 8.1, but I pushed it to
>> master now, along with the prerequisite patch.
>>
> 
> Hi,
> 
> This caused GDB to fail to build for arm-none-eabi targets
> ../../../gdb/remote-sim.c: In function 'void init_gdbsim_ops()':
> ../../../gdb/remote-sim.c:1342:27: error: invalid conversion from
> 'void (*)(target_ops*, ptid_t)' to 'void (*)(target_ops*)'
> [-fpermissive]
>    gdbsim_ops.to_interrupt = gdbsim_interrupt;
>                            ^
> make[2]: *** [remote-sim.o] Error 1
> make[2]: *** Waiting for unfinished jobs....
> ../../../gdb/cli/cli-cmds.c: In function 'void complete_command(const
> char*, int)':
> ../../../gdb/cli/cli-cmds.c:304:48: warning: 'word' may be used
> uninitialized in this function [-Wmaybe-uninitialized]
>          get_max_completions_reached_message ());
>                                                 ^
> ../../../gdb/cli/cli-cmds.c:277:71: warning: 'tracker' may be used
> uninitialized in this function [-Wmaybe-uninitialized]
>      = tracker->build_completion_result (word, word - arg, strlen (arg));
> 
> (building in an Ubuntu Trusty container)
> 
> Can you fix it ?

Sorry about that.  Don't know how I missed this to_interrupt
implementation.  And windows-nat.c too.  I'll take a look.

Thanks,
Pedro Alves


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