[Libguestfs] alternatives for hooking dlopen() without LD_LIBRARY_PATH or LD_AUDIT?

[Eric Blake]

On 2/14/20 1:02 PM, Eric Blake wrote:

> Writing my own dlopen() wrapper directly in nbdkit seems like a 
> non-starter (my override has to come from a shared library before it can 
> replace the shared version that would be imported from -ldl, at least 
> for all subsequent shared library loads that want to bind to the 
> override).

Maybe I spoke too soon. I've tried another approach that looks like it 
will do what I want: put my shim dlopen() in a shared library, but link 
nbdkit against that shared library PRIOR to -ldl (so that name lookup 
for dlopen resolves there first).  The shim library in turn depends on 
-ldl so that dlsym(RTLD_NEXT, "dlopen") still lets me get to the real 
dlopen.  And by linking it directly into nbdkit, rather than into the 
nbdkit-vddk-plugin.so that gets loaded later, the first bound dlopen() 
in use for all subsequent loads is from my shim.  It's still a bit less 
clean than I'd like (it requires tighter coupling between nbdkit and 
nbdkit-vddk-plugin.so than what used to exist), but the fact that it 
works without dlmopen() or LD_LIBRARY_PATH is in its favor.  I'm now 
polishing up the experiment, and will post the patch when it's ready.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org