Re: debuginfo server progress update

[Aaron Merey <amerey@redhat.com>]

Hi Mark,

On Fri, Jul 5, 2019 at 12:46 PM Mark Wielaard <mark@klomp.org> wrote:
>
> Hi Aaron,
>
> On Wed, Jul 03, 2019 at 03:59:46PM -0400, Aaron Merey wrote:
> > The debuginfo server, a web service that offers lightweight on-demand lookups
> > of debuginfo-related data, along with its elfutils client have begun to take
> > shape so I want to provide an update on where we currently are in its
> > development and how to use it.
> >
> > We plan on shipping debuginfo server with elfutils and it is currently
> > available on the branch 'fche/dbgserver' of the elfutils git repo.
>
> And now also simply on 'dbgserver'.
> https://sourceware.org/git/?p=elfutils.git;a=shortlog;h=refs/heads/dbgserver
>
> > The
> > http web server itself is able to scan a directory tree for any debuginfo,
> > executable and source files and index them by build-id. The elfutils client
> > hooks into libdwfl and provides a fallback so that if the library is not able
> > to locate a debuginfo file, the client, if enabled, will attempt to query
> > debuginfo servers for debuginfo containing a particular build-id.
> > [...]
> > This time systemtap successfully acquires the debuginfo and begins running
> > the probe. Although in this example everything is running locally, the server
> > and the debuginfo could just as well be on a remote host.
> >
> > Debuginfo server development is ongoing. Some of the features we have planned
> > include a gdb client that could query debuginfo servers for debuginfo or source
> > code and the ability for the server to automatically search rpms for any of the
> > files requested by a client. We also are planning a talk/demo at GNU Cauldron
> > this September in Montréal, Canada (https://gcc.gnu.org/wiki/cauldron2019).
> >
> > Hopefully this helped give you a sense of how to use debuginfo server, where it
> > is in its development, and what is to come. Feedback is always appreciated!
>
> I think it would be nice if there was a dbgclient binary that could be
> reused by multiple clients.  It could do most of what you currently do
> in libdwfl/dbgserver-client.c. It would simply take a buildid and type
> (exec, dbg, src) and return a file path to the resulting file when
> found (or a well defined error number when not found).
>
> Such a dbgclient executable would make writing other clients
> easier. For example dbgserver_build_id_find would simply reduce to
> spawning dbgclient with the right arguments and opening the resulting
> file path. Other clients, like gdb, then also don't need to implement
> the caching and quering, but can also simply call dbgclient <build-id>
> <type> and just open the resulting file.

I really like this suggestion, even with just elfutils and gdb clients
there will
already be too much code duplication if we don't have the client code in its own
binary. This raises questions such as whether dbgclient should be a shared
library or a command line tool, but regardless of these implementation details
you bring up an issue that needs to be addressed as the client side of debuginfo
server grows. I appreciate the feedback!

Aaron