Message-ID: <4F3DB9E8.7040406@zytor.com>
Date: Thu, 16 Feb 2012 18:22:32 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Andrew Lutomirski <luto@mit.edu>
CC: Indan Zupancic <indan@nul.nu>, Will Drewry <wad@chromium.org>,
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Subject: Re: [PATCH v8 3/8] seccomp: add system call filtering using BPF
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On 02/16/2012 06:16 PM, Andrew Lutomirski wrote:
> 
> Is there really no syscall that cares about endianness?
> 
> Even if it ends up working, forcing syscall arguments to have a
> particular endianness seems like a bad decision, especially if anyone
> ever wants to make a 64-bit BPF implementation.  (Or if any
> architecture adds 128-bit syscall arguments to a future syscall
> namespace or whatever it's called.  x86-64 has 128-bit xmm
> registers...)
> 

Not to mention that the reshuffling code will add totally unnecessary
cost to the normal operation.  Either way, Indan has it backwards ... it
*is* one field, the fact that two operations is needed to access it is a
function of the underlying byte code, and even if the byte code can't
support it, a JIT could merge adjacent operations if 64-bit operations
are possible -- or we could (and arguably should) add 64-bit opcodes in
the future for efficiency.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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