linux-kernel - Re: [ofa-general] [PATCH 2.6.30] RDMA/cxgb3: Remove modulo math.

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: <20090210.170740.208470781.davem@davemloft.net>
Date:	Tue, 10 Feb 2009 17:07:40 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	swise@...ngridcomputing.com
Cc:	rdreier@...co.com, randy.dunlap@...cle.com,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	general@...ts.openfabrics.org
Subject: Re: [ofa-general] [PATCH 2.6.30] RDMA/cxgb3: Remove modulo math.

From: Steve Wise <swise@...ngridcomputing.com>
Date: Tue, 10 Feb 2009 19:03:52 -0600

> Roland Dreier wrote:
> > I'll roll this into the offending patch (that is in -next).
> >
> > But:
> >
> >  > -		wqe->recv.sgl[i].to = cpu_to_be64(((u32) wr->sg_list[i].addr) %
> >  > -				(1UL << (12 + page_size[i])));
> >  > +		wqe->recv.sgl[i].to = cpu_to_be64(((u64) wr->sg_list[i].addr) &
> >  > +				((1UL << (12 + page_size[i]))-1));
> >
> > Is this required?  Strength reduction optimization should do this
> > automatically (and the code has been there for quite a while, so
> > obviously it isn't causing problems)
> >
> >  - R.
> >   
> Ok.

GCC won't optimize that modulus the way you expect, try for yourself
and look at the assembler if you don't believe me. :-)

--
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/