Re: [PATCH 2/4] Add Jeff Mahoney's py-crash patches.

[Petr Tesarik <ptesarik at suse dot cz>]

Hi Doug,

On Wed, 3 Feb 2016 10:30:20 -0800
Doug Evans <dje@google.com> wrote:

> On Wed, Feb 3, 2016 at 9:55 AM, Jeff Mahoney <jeffm@suse.com> wrote:
> >...
> >>> Hi.
> >>
> >> Hi Doug -
> >>
> >>> Part of what this patch is doing is exporting bfd to python.
> >>> E.g., all the SEC_* constants.
> >>
> >>> As a rule we absolutely discourage people from using bfd outside
> >>> of the the binutils+gdb source tree. Either this rule needs to
> >>> change, or I don't think we can allow this patch. I'd be
> >>> interested to hear what others in the community think.
> >>
> >> That's unfortunate.  The Linux kernel uses ELF sections for a
> >> number of purposes.  Most notably is the definition of per-cpu
> >> variables. Without the ELF section, we can't resolve the addresses
> >> for the variables.  So, from our perspective, it's a requirement.
> >>
> >>> For myself, I would much rather export ELF separately (e.g., a
> >>> separate python API one can use independent of any particular
> >>> tool, including gdb), and then have gdb provide the necessary
> >>> glue to use this API. [I can imagine some compromises being
> >>> needed, at least for now; e.g., it'd be cumbersome to read in all
> >>> ELF symbols twice. But fixing that is just an optimization.]
> >>
> >> Ok, that's doable.  As it is, the section code mixes GDB and BFD
> >> pretty heavily.  It shouldn't be too difficult to separate the two
> >> out and push the section stuff into a new BFD python interface and
> >> associate the objfiles with it.
> >
> > And here's what I've come up with.  Does this constitute enough of a
> > separation?  It /should/ cross over into the BFD code in the same way
> > that the GDB code does: As soon as we hit a bfd object or a
> > bfd_section object, we call into bfd's new python API to generate the
> > objects.
> >
> > https://jeffm.io/git/cgit.cgi/gnu/binutils-gdb/log/?h=gdb/python-bfd
> >
> > For the fully-integrated kdump work, use the python-bfd-kdump branch
> > (or SUSE folks, python-bfd-kdump-buildid will pick up the separate
> > debuginfos as we usually expect).
> 
> Separation isn't the issue, unfortunately.
> The issue is that we cannot export bfd to python, period.

Excuse my ignorance, but can you explain a bit more why BFD should not
be used? I'm sure there has been some discussion on that topic; a
pointer in the right direction would be welcome.

TIA,
Petr Tesarik