Pre-startup segmentation fault with ptrace

I have somehow managed to mangle my computer so that any time I attempt to use something that uses ptrace to trace another process (eg strace, gdb), I get an immediate segmentation fault.

For example:

# strace /bin/true
execve("/bin/true", ["/bin/true"], [/* 27 vars */]) = 0
--- SIGSEGV (Segmentation fault) @ 0 (0) ---
+++ killed by SIGSEGV +++

or with gdb:

# gdb /bin/true
GNU gdb Fedora (6.8-27.el5)
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu"...
(no debugging symbols found)
(gdb) run
Starting program: /bin/true 

Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.
You can't do that without a process to debug.

rpm -V comes up clean on strace, gdb, and glibc. I do not have any LD_* variables set, and PATH has nothing special in it.

Update: problem is in the kernel-2.6.18-128 kernel when recompiled with PREEMPT. That kernel emulates ptrace with the utrace infrastructure, and it seems to disagree with preemption. kernel-2.6.18-164 seems to fix it.