[PATCH v3] debuginfod: Support queries for ELF/DWARF sections

[Mark Wielaard]

Hi Aaron,

On Tue, Nov 01, 2022 at 12:53:41AM -0400, Aaron Merey wrote:
> Thanks again for the detailed review.  I fixed the issues you pointed out.

This version looks really good. Please push, so it is included in the
release tomorrow.

> On Sat, Oct 29, 2022 at 8:29 PM Mark Wielaard <mark@klomp.org> wrote:
> > > @@ -1008,6 +1206,9 @@ debuginfod_query_server (debuginfod_client *c, 
> > >            snprintf(data[i].url, PATH_MAX, "%s/%s/%s/%s", server_url,
> > >                     build_id_bytes, type, escaped_string);
> > >          }
> > > +      else if (section)
> > > +     snprintf(data[i].url, PATH_MAX, "%s/%s/%s/%s", server_url,
> > > +              build_id_bytes, type, section);
> >
> > Does the section part need to be path escaped? Like the filename is
> > with curl_easy_escape? And if it is how does that interact with the 
> > cache file name?
> 
> I assumed that section names would not contain '/'.  However I noticed
> that if we call debuginfod_find_section with a section name containing
> '/', it will return -EINVAL.  This triggers the downloading of debuginfo
> in order to attempt client-side extraction.  This is a waste so I changed
> the client to path-escape the section name for caching purposes just like
> the source query filename.

It is highly unlikely a '/' is in the section name, but good to have
this covered anyway. Nicely extracted that escape function.

> > > +  /* The servers may have lacked support for section queries.  Attempt to
> > > +     download the debuginfo or executable containing the section in order
> > > +     to extract it.  */ 
> >
> > This does somewhat defeat the purpose of just getting the section data
> > of course. So we could also just return EINVAL to the user here, so
> > they have to get the whole debuginfo themselves. But maybe just
> > pretending it worked is fine to keep the code path of the user
> > simpler?
> 
> This keeps the code path simpler for the user and like Frank mentioned
> it enables an intermediate server to extract the section and provide
> it to the client.  This server will also cache the debuginfo/executable,
> possibly speeding up future requests.

Ah, yes, the debuginfod server doesn use the client library too.

Thanks,

Mark