Using GDB as a Python interpreter

Using GDB as a Python interpreter

[Florian Weimer]

I want to run a Python script with GDB, from the shell command line,
without having to create two files.

I came up with the hack included below, but it's not particularly nice.
The downside is that the script file name must end in “.py”, which would
not allow to install the script in /usr/bin for most distributions.  I
don't see a way to override that.

Thanks,
Florian

#!/usr/bin/python

if 'gdb' not in globals():
    import sys
    import os

    pid, = sys.argv[1:]
    os.execvp('gdb', [
        'gdb', '--batch',
        '-ex', 'set debuginfod enabled off',
        '-ex', 'attach ' + pid,
        '-x', __file__,
    ])

dl_ns = gdb.lookup_global_symbol('_rtld_global').value()['_dl_ns']
nsid_min, nsid_max = dl_ns.type.range()
for nsid in range(nsid_min, nsid_max + 1):
    l = dl_ns[nsid]['_ns_loaded']
    if not l:
        continue
    print('namespace', nsid)
    while l:
        print('  {!r}'.format(l['l_name'].string()))
        ln = l['l_libname']
        while ln:
            print('    alias {!r}'.format(ln['name'].string()))
            ln = ln['next']
        l = l['l_next']

RE: Using GDB as a Python interpreter

[Aktemur, Tankut Baris]

On Saturday, July 1, 2023 10:53 AM, Florian Weimer wrote:
> I want to run a Python script with GDB, from the shell command line,
> without having to create two files.
> 
> I came up with the hack included below, but it's not particularly nice.
> The downside is that the script file name must end in “.py”, which would
> not allow to install the script in /usr/bin for most distributions.  I
> don't see a way to override that.

Based on this comment, I assume you have write access to /usr.
Would you then consider wrapping your script in a Python function
and then installing it in GDB's data directory
(e.g. /usr/share/gdb/python/gdb/function/)?  The file would be loaded
automatically by GDB at startup.  You can then invoke the Python function
with a single-line GDB command.

-Baris

 
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Re: Using GDB as a Python interpreter

[Florian Weimer]

* Tankut Baris via Gdb Aktemur:

> On Saturday, July 1, 2023 10:53 AM, Florian Weimer wrote:
>> I want to run a Python script with GDB, from the shell command line,
>> without having to create two files.
>> 
>> I came up with the hack included below, but it's not particularly nice.
>> The downside is that the script file name must end in “.py”, which would
>> not allow to install the script in /usr/bin for most distributions.  I
>> don't see a way to override that.
>
> Based on this comment, I assume you have write access to /usr.
> Would you then consider wrapping your script in a Python function
> and then installing it in GDB's data directory
> (e.g. /usr/share/gdb/python/gdb/function/)?  The file would be loaded
> automatically by GDB at startup.  You can then invoke the Python function
> with a single-line GDB command.

I was aiming for a one-file solution (and something that could be
installed as-is into /usr/bin eventually).  Two-file solutions are sort
of easy. 8-)

Thanks,
Florian

Re: Using GDB as a Python interpreter

[Tom Tromey]

>>>>> "Florian" == Florian Weimer via Gdb <gdb@sourceware.org> writes:

Florian> I want to run a Python script with GDB, from the shell command line,
Florian> without having to create two files.

Once upon a time, Red Hat had a patch to add a '-P' option to gdb, which
would put it directly into Python scripting.  I think maybe I wrote it
ages ago, but then when Andrew tried to submit it upstream, I basically
rejected it.

That was a mistake on my part.  IIRC he had a pretty good
counter-argument at the time, I don't recall why I didn't recant.

Another option I looked at, way back when, was to compile gdb with -fPIE
and let it be loaded as a shared library.  The idea here was that, with
a few other tweaks, ordinary Python code could just 'import gdb'.

Anyway, I guess now I'd support either of these.  'import gdb' would be
great to have, even with its various limitations.  However it's a bit
trickier to get working than just resurrecting the old -P patch.

Tom

Re: Using GDB as a Python interpreter

[Mark Wielaard]

On Mon, Jul 03, 2023 at 01:39:34PM -0600, Tom Tromey wrote:
> >>>>> "Florian" == Florian Weimer via Gdb <gdb@sourceware.org> writes:
> 
> Florian> I want to run a Python script with GDB, from the shell command line,
> Florian> without having to create two files.
> 
> Once upon a time, Red Hat had a patch to add a '-P' option to gdb, which
> would put it directly into Python scripting.  I think maybe I wrote it
> ages ago, but then when Andrew tried to submit it upstream, I basically
> rejected it.
> 
> That was a mistake on my part.  IIRC he had a pretty good
> counter-argument at the time, I don't recall why I didn't recant.

Was that this?
https://inbox.sourceware.org/gdb-patches/20190721235427.21893-1-kevinb@redhat.com/

Cheers,

Mark

Re: Using GDB as a Python interpreter

[Tom Tromey]

Mark> Was that this?
Mark> https://inbox.sourceware.org/gdb-patches/20190721235427.21893-1-kevinb@redhat.com/

Yeah, and I mis-remembered who sent it upstream, sorry about that!

Tom