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Re: [PATCH] incorrect asm constraints for ll/sc constructs

To: Ralf Baechle <ralf@oss.sgi.com>
Subject: Re: [PATCH] incorrect asm constraints for ll/sc constructs
From: Daniel Jacobowitz <dan@debian.org>
Date: Fri, 25 May 2001 13:49:09 -0700
Cc: linux-mips@oss.sgi.com
In-reply-to: <20010525172746.B6578@bacchus.dhis.org>; from ralf@oss.sgi.com on Fri, May 25, 2001 at 05:27:46PM -0300
References: <20010523145257.A13013@nevyn.them.org> <Pine.GSO.3.96.1010524134521.6990F-100000@delta.ds2.pg.gda.pl> <20010525172746.B6578@bacchus.dhis.org>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.3.16i
On Fri, May 25, 2001 at 05:27:46PM -0300, Ralf Baechle wrote:
> On Thu, May 24, 2001 at 03:42:56PM +0200, Maciej W. Rozycki wrote:
> 
> > > The ll/sc constructs in the kernel use ".set noat" to inhibit use of $at,
> > > and proceed to use it themselves.  This is fine, except for one problem: 
> > > the
> > > constraints on memory operands are "o" and "=o", which means offsettable
> > > memory references.  If I'm not mistaken, the assembler will (always?)
> > > turn these into uses of $at if the offset is not 0 - at least, it 
> > > certainly
> > > seems to do that here (gcc 2.95.3, binutils 2.10.91.0.2).  Just being 
> > > honest
> > > with the compiler and asking for a real memory reference does the trick. 
> > 
> >  Both "m" and "o" seem to be incorrect here as both are the same for MIPS; 
> > "R" seems to be appropriate, OTOH.  Still gcc 2.95.3 doesn't handle "R" 
> > fine for all cases, but it works most of the time and emits a warning
> > otherwise.  I can't comment on 3.0.
> 
> I admit the construction is somewhat fragile and will take any patches to
> cleanup this.

How about the attached, then?  If the p[0x100000] case is of sufficient
concern, we can work around that too, but this catches all current
uses.

-- 
Daniel Jacobowitz                           Debian GNU/Linux Developer
Monta Vista Software                              Debian Security Team

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