[Bug dap/30472] New: DAP "repl" evaluation can make gdb unresponsive

[Bug dap/30472] New: DAP "repl" evaluation can make gdb unresponsive

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

            Bug ID: 30472
           Summary: DAP "repl" evaluation can make gdb unresponsive
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: dap
          Assignee: unassigned at sourceware dot org
          Reporter: tromey at sourceware dot org
  Target Milestone: ---

gdb implements the "repl" context for the "evaluate" request
by passing the string to gdb as a command.
However, if the command is something like "continue", gdb will
simply continue -- but the DAP thread will presumably wait,
because eval_request uses send_gdb_with_response.

At least... I think this should happen.  Step 1 would be to write
a test for this.  Then, if it fails, some solution would have to
be found.  Perhaps a global flag to automatically treat continue
commands as if they had a "&" would work.

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[Bug dap/30472] DAP "repl" evaluation can make gdb unresponsive

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
It occurs to me that this could also happen with the "target"
command, and for that one, "&" isn't implemented.

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[Bug dap/30472] DAP "repl" evaluation can make gdb unresponsive

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

--- Comment #2 from Tom Tromey <tromey at sourceware dot org> ---
See bug#7251.  Bug #7253 is also maybe relevant.

Maybe it would be enough to use send_gdb and then
have any output from the command be sent as output
events, not in the response.  Then the reader thread
could accept interrupt requests.

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[Bug dap/30472] DAP "repl" evaluation can make gdb unresponsive

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
Most of the problem could be solved by noticing when
the inferior continues and telling the DAP response that
it is done.
This wouldn't help with the "target" problem though.

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[Bug dap/30472] DAP "repl" evaluation can make gdb unresponsive

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

--- Comment #4 from Tom Tromey <tromey at sourceware dot org> ---
I realized somewhat belatedly that this problem also
affects evaluation of expressions that involve an
inferior call.  These can't be handled by changing
how the output is directed.

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[Bug dap/30472] DAP "repl" evaluation can make gdb unresponsive

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

--- Comment #5 from Tom Tromey <tromey at sourceware dot org> ---
I was thinking this could be handled by implementing cancellation,
but that will give weird results when used to interrupt an
inferior call.  Like, I suppose it would work, but the inferior
will be left in a somewhat weird state.

Also it seems a little strange to use cancellation to interrupt
a gdb CLI "continue" but not a DAP "continue".

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[Bug dap/30472] DAP "repl" evaluation can make gdb unresponsive

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

--- Comment #6 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to Tom Tromey from comment #5)

> Also it seems a little strange to use cancellation to interrupt
> a gdb CLI "continue" but not a DAP "continue".

I go back and forth on this, but I suppose the difference is
that a repl evaluation of "continue" won't return a result,
so cancel would be correct.

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[Bug dap/30472] DAP "repl" evaluation can make gdb unresponsive

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |tromey at sourceware dot org

--- Comment #7 from Tom Tromey <tromey at sourceware dot org> ---
I'm working on this.

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[Bug dap/30472] DAP "repl" evaluation can make gdb unresponsive

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

--- Comment #8 from Tom Tromey <tromey at sourceware dot org> ---
https://sourceware.org/pipermail/gdb-patches/2023-December/204689.html

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[Bug dap/30472] DAP "repl" evaluation can make gdb unresponsive

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

--- Comment #9 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom Tromey <tromey@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=1c79c8dad90e4382100b51694a2b9ee7e913a04a

commit 1c79c8dad90e4382100b51694a2b9ee7e913a04a
Author: Tom Tromey <tromey@adacore.com>
Date:   Tue Nov 7 10:56:07 2023 -0700

    Implement DAP cancellation

    This implements DAP cancellation.  A new object is introduced that
    handles the details of cancellation.  While cancellation is inherently
    racy, this code attempts to make it so that gdb doesn't inadvertently
    cancel the wrong request.

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30472
    Approved-By: Eli Zaretskii <eliz@gnu.org>
    Reviewed-By: Kévin Le Gouguec <legouguec@adacore.com>

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[Bug dap/30472] DAP "repl" evaluation can make gdb unresponsive

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30472

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|---                         |15.1
             Status|NEW                         |RESOLVED

--- Comment #10 from Tom Tromey <tromey at sourceware dot org> ---
Fixed.

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