netdev - Re: [PATCH net-next v3 8/9] net: filter: rework/optimize internal BPF interpreter's instruction set

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Date:	Thu, 27 Mar 2014 15:23:19 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	dborkman@...hat.com
Cc:	ast@...mgrid.com, netdev@...r.kernel.org, hagen@...u.net,
	keescook@...omium.org, pmoore@...hat.com, mingo@...nel.org,
	hpa@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 8/9] net: filter: rework/optimize internal
 BPF interpreter's instruction set

From: Daniel Borkmann <dborkman@...hat.com>
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.
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