Does gdb debuginfod download libc etc.?

I'm trying to start using debuginfod support in my environment.  I've
started my own debuginfod server and I've added lots of historical
binaries and shared libraries that I get core files from.

In that past I've asked users to package up all their system libraries
such as libc.so, libm.so, libpthread.so, the runtime linker ld-linux.so
etc. and send them along with their core file.  Then I run GDB like:
  gdb -iex 'set sysroot xxx' -c core exe

What I was hoping to do is to run "gdb -c core" and have debuginfod get
everything I need without having to ask users to send anything
(assuming I've already got the libraries, which I usually do).  But, it
doesn't seem to be working.

I've used debuginfod-find to verify that all the libraries referenced
by the core file do exist on the server (via their build ID).

When I run "gdb -c core" it DOES correctly download the executable
file, so I know that GDB's debuginfod configuration is working.  It
also appears to download linux-vdso.so.1.

However, none of my other libraries are being loaded, even if I use bt
or whatever to look at the backtrace.  Without libc for example, none
of the threads which were in the C runtime when the core was taken can
be traced and I just get "?? ()" for every frame.  If I use "info
sharedlib" I see all the .so paths are the local system versions of
these libraries, and they have a "Syms Read" value of "No".


Is there something else I need to do to get this working?

Or am I just misunderstanding how debuginfod support works?