From: Daniel Borkmann <redacted>
Date: Wed, 26 Mar 2014 22:06:09 +0100

  - Adds swab insns for 32/64-bit

I don't like this.

You don't want a swab instruction, you want "endian X to endian Y".  Just
like we have "cpu_to_le32()", "le32_to_cpu()" et al. in the kernel.

That way the user can be completely oblivious as to the endianness of
the cpu it's running on.

So if you ask for a "to little endian" swab, if the chip is
little-endian then no code needs to be emitted at all, it's a nop.

There is zero reason for the BPF program emitted by userspace to be
dependant upon the cpu endianness.