If you need to debug something in the early
ld.so startup, and can't refrain
from good old
printf debugging, there is a caveat: the available API in
ld.so is rather limited. See the few functions is
example, there's a private
__libc_write, which you should be able to use for
writing to FD stderr -- but, at early
ld.so startup, this isn't usable as
_hurd_init_dtable is still all zeros, etc. To get you started, here is a
simple dl-sysdep.c.patch to get access to the Mach console.
Can this be integrated with the other debugging printf functions from
_dl_debug_vdprintf) (open issue glibc)?