I was very lazy and symlinked /bin/sh to /bin/busybox to edit some bourne shell scripts and promptly forgot about it until my latest emerge world. dev-python/numpy and media-video/mplayer both failed to link because libraries were being created with busybox's ar (which doesn't support creating an index). Steps to reproduce, ie. with numpy: # ln -s /bin/busybox /bin/sh # emerge dev-python/numpy - observe link failures # which ar - note the use of busybox's ar instead of the ar in our $PATH There may be other packages other than numpy and mplayer effected by this oddity.
This is to be expected.