Last time I used it, crosstool was painless, but I guess you'd prefer this link to x86 cross-compilers that akpm posted the other month: http://developer.osdl.org/dev/plm/cross_compile/
It seems like CROSS_COMPILE= should not be needed if my standard gcc
binary can produce x86-64 code. I was hoping it would be possible to
build an x86-64 kernel using the Ubuntu packages and that I would not
have to resort to building my own toolchain. And it seems that it's
supposed to work, but doesn't.