[[!meta copyright="Copyright © 2011, 2013 Free Software Foundation, Inc."]] [[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable id="license" text="Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled [[GNU Free Documentation License|/fdl]]."]]"""]] 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 `dl-sysdep.c`. For 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. [[!message-id desc="Original submission" "87y5vrpnvi.fsf@gnu.org"]]. Can this be integrated with the other debugging printf functions from `elf/dl-misc.c` (`_dl_debug_vdprintf`) ([[!taglink open_issue_glibc]])? In 2013-01, the [[microkernel/mach/gnumach/interface/syscall/mach_print]] [[system_call]] has been added to [[GNU Mach|microkernel/mach/gnumach]]. It is available when the kernel is built with the in-kernel kdb debugger.