How to reproduce:

# mkdir /mnt/readonly
# mount --bind / /mnt/readonly
# mount -o remount,ro /mnt/readonly
# mount -t proc proc /mnt/readonly/proc
# chroot /mnt/readonly python3.2 -c "import ctypes"
Segmentation fault

If your python build expected to have this bug, you'll see something like this (the -1 EROFS lines):

# chroot /mnt/readonly strace -f -e trace=open python3.2 -c "import ctypes" 2>&1 | grep ffi
open("/usr/lib/libffi.so.5", O_RDONLY)  = 5
open("/tmp/.private/root/ffiicoh8G", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 ENOENT (No such file or directory)
open("/tmp/ffiFjqUa9", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 EROFS (Read-only file system)
open("/var/tmp/ffidTdydB", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 EROFS (Read-only file system)
open("/dev/shm/ffiemIcg3", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 EROFS (Read-only file system)
open("/root/ffiXfWRiv", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 EROFS (Read-only file system)