[Bug cli/28041] New: Memory leak upon prefix redefinition

[Bug cli/28041] New: Memory leak upon prefix redefinition

[quentin at minster dot io]

https://sourceware.org/bugzilla/show_bug.cgi?id=28041

            Bug ID: 28041
           Summary: Memory leak upon prefix redefinition
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: cli
          Assignee: unassigned at sourceware dot org
          Reporter: quentin at minster dot io
  Target Milestone: ---

Created attachment 13522
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13522&action=edit
test.gdb

>From Python, when defining a prefix/command with the same name as an existing
prefix, the existing prefix gets deleted but not its subcommands. This results
in a memory leak, or in strange behavior if some Python objects still refer to
the undeleted-but-uninvokable subcommand.

Attached is a sample test.gdb script that demonstrates the issue (works at
least on `gdb-10-branch` HEAD, 10.2 & 10.1): after redefinition of prefix
"foo", the Python object for command "foo bar", though unreferenced, is not
deleted.
Also, it is still reachable through the "bar" alias, which is confusing because
the new prefix "foo" doesn't contain any subcommands.

Buggy output:

  $ gdb -q -x test.gdb
  DEL PREFIX foo
  HOOK foo
  COMMAND foo
  HOOK foo bar
  COMMAND foo bar

This issue doesn't seem to arise when defining the prefixes/commands using
`define` and `define-prefix`, because re-definition of an existing prefix just
seems to modify the existing prefix.

Attached is also a patch to fix this issue: when deleting a prefix in
`delete_cmd()`, also delete all its subcommands and their aliases.
After applying the fix, the subcommands of the deleted prefix are indeed
deleted (and their Python objects released), as are their aliases, as is
illustrated by the same sample test.gdb script.

Fixed output:

  $ gdb -q -x test.gdb
  DEL PREFIX foo
  DEL COMMAND foo bar
  HOOK foo
  COMMAND foo
  test.gdb:53: Error in sourced command file:
  Undefined command: "bar".  Try "help".

Please feel free to request more details, or suggest corrections/improvements
to the patch.

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[Bug cli/28041] Memory leak upon prefix redefinition

[quentin at minster dot io]

https://sourceware.org/bugzilla/show_bug.cgi?id=28041

--- Comment #1 from Quentin Minster <quentin at minster dot io> ---
Created attachment 13523
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13523&action=edit
0001-gdb-Fix-memory-leak-of-subcommands-when-deleting-a-p.patch

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[Bug cli/28041] Memory leak upon prefix redefinition

[quentin at minster dot io]

https://sourceware.org/bugzilla/show_bug.cgi?id=28041

Quentin Minster <quentin at minster dot io> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |quentin at minster dot io

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[Bug cli/28041] Memory leak upon prefix redefinition

[simark at simark dot ca]

https://sourceware.org/bugzilla/show_bug.cgi?id=28041

Simon Marchi <simark at simark dot ca> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |simark at simark dot ca

--- Comment #2 from Simon Marchi <simark at simark dot ca> ---
Hi Quentin,

If you'd like to get your patch reviewed, please send your patch to the
gdb-patches list.  See: https://sourceware.org/gdb/wiki/ContributionChecklist

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