linux-kernel - Re: Specific support for Intel Atom architecture

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20090512181338.GK19296@one.firstfloor.org>
Date:	Tue, 12 May 2009 20:13:38 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Ulrich Drepper <drepper@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Tobias Doerffel <tobias.doerffel@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Specific support for Intel Atom architecture

On Tue, May 12, 2009 at 10:45:00AM -0700, Ulrich Drepper wrote:
> On Tue, May 12, 2009 at 8:04 AM, Andi Kleen <andi@...stfloor.org> wrote:
> > The problem is that you can't express the situations where
> > movbe is better than bswap (you need both and the old and the new
> > value) in inline assembler in a way that gcc decides automatically.
> 
> True.  But I was mostly thinking about loads from memory.  A quick
> search for ntoh*/hton* shows code like
> 
>         u_int16_t queue_num = ntohs(nfmsg->res_id);
> 
> If there would be a ntohs_load() macro movbe could be used.

It wouldn't surprise me if

	movbe memory,%reg

generates the same uops sequence internally as

	mov memory,%reg
	bswap %reg

I doubt there's any dedicated hardware for this in Atom (but I don't
know for sure) 

So unless you're really decoding constrained it would only
save a few bytes of code size. Probably not worth having 
incompatible modules for or adding special code to the source.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/