Re: [PATCH 1/3] gdb/python: introduce gdb.Corefile API

[Eli Zaretskii <eliz@gnu.org>]

> From: Andrew Burgess <aburgess@redhat.com>
> Cc: Andrew Burgess <aburgess@redhat.com>
> Date: Tue,  2 Sep 2025 17:03:49 +0100
> 
> This commit starts adding some core file related features to the
> Python API.
> 
> In this initial commit I've tried to keep the changes as small as
> possible for easy review.
> 
> There's a new Python class gdb.Corefile, which represents a loaded
> core file.  This API doesn't allow the user to create their own
> gdb.Corefile objects, a core file must be loaded using the 'core-file'
> command, then a gdb.Corefile object can be obtained by querying the
> inferior in which the core file was loaded.
> 
> There's a new attribute gdb.Inferior.corefile, this is None when no
> core file is loaded, or contains a gdb.Corefile object if a core file
> has been loaded.
> 
> Currently, the gdb.Corefile object has one attribute, and one method,
> these are:
> 
>   gdb.Corefile.filename -- the file name of the loaded core file.
> 
>   gdb.Corefile.is_valid() -- indicates if a gdb.Corefile object is
>   valid or not.  See notes below.
> 
> A gdb.Corefile object is only valid while the corresponding core file
> is loaded into an inferior.  Unloading the core file, or loading a
> different one will cause a gdb.Corefile object to become invalid.  For
> example:
> 
>   (gdb) core-file /tmp/core.54313
>   ... snip ...
>   (gdb) python core=gdb.selected_inferior().corefile
>   (gdb) python print(core)
>   <gdb.Corefile inferior=1 filename='/tmp/core.54313'>
>   (gdb) python print(core.is_valid())
>   True
>   (gdb) core-file
>   No core file now.
>   (gdb) python print(core)
>   <gdb.Corefile (invalid)>
>   (gdb) python print(core.is_valid())
>   False
>   (gdb)
> 
> In order to track changes to the core file, there is a new observable
> 'core_file_changed', which accounts for the changes in corelow.c,
> observable,c, and observable.h.  Currently, this observable is not
> visible as a Python event.
> 
> I chose to access the core file via the inferior even though the core
> file BFD object is actually stored within the program_space.  As such,
> it might seem that the natural choice would be to add the attribute as
> gdb.Progspace.corefile.
> 
> For background reading on my choice, please see:
> 
>   https://inbox.sourceware.org/gdb-patches/577f2c47793acb501c2611c0e6c7ea379f774830.1668789658.git.aburgess@redhat.com
> 
> This patch was never merged, it is still on my backlog, but the
> observation in that work is that some targets are not really
> shareable.  For example, the core_target (corelow.c) stores
> information about the loaded core file within the target instance.  As
> such, each target instance represents a single loaded core file.
> 
> Except that the BFD part of the core file is stored in the
> program_space, which is a little weird.
> 
> During review, Tom made the observation, that maybe we should
> investigate moving the core file BFD into the core_target.  I'm
> inclined to agree with this as a direction of travel.
> 
> All this leaves us with two observations:
> 
>   1. Currently, loading a core file into an inferior, then using
>      'add-inferior' will try to share the core_target between
>      inferiors.  This is broken, and can trigger GDB crashes.  The
>      obvious fix, without reworking core_target, is just to prevent
>      this sharing, making core_target per-inferior.
> 
>   2. Having the core file information split between the core_target
>      instance, and the BFD stored in the program_space is a little
>      weird, and is really just historical.  Planning for a future
>      where the BFD is also stored in the core_target might be wise.
> 
> So, if we imagine that the BFD is (one day) moved into the
> core_target, and that the core_target really becomes non-shareable,
> then it is, I think, clearer that the corefile attribute should live
> on the gdb.Inferior object, not the gdb.Progspace object.
> 
> There's testing for all the functionality added in this commit.
> 
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32844
> ---
>  gdb/Makefile.in                          |   1 +
>  gdb/NEWS                                 |  10 +
>  gdb/corelow.c                            |   7 +
>  gdb/doc/python.texi                      |  49 ++++
>  gdb/observable.c                         |   1 +
>  gdb/observable.h                         |   6 +
>  gdb/python/py-corefile.c                 | 293 +++++++++++++++++++++++
>  gdb/python/py-inferior.c                 |  18 ++
>  gdb/python/python-internal.h             |   8 +
>  gdb/testsuite/gdb.python/py-corefile.c   |  25 ++
>  gdb/testsuite/gdb.python/py-corefile.exp | 169 +++++++++++++
>  11 files changed, 587 insertions(+)
>  create mode 100644 gdb/python/py-corefile.c
>  create mode 100644 gdb/testsuite/gdb.python/py-corefile.c
>  create mode 100644 gdb/testsuite/gdb.python/py-corefile.exp

Thanks, the documentation parts are okay.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>