From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id 4DBF3DDFB4 for ; Wed, 30 May 2007 21:44:54 +1000 (EST) Subject: Re: Saving to 32 bits of GPRs in signal context From: Benjamin Herrenschmidt To: Kumar Gala In-Reply-To: References: <18012.61822.197988.279764@cargo.ozlabs.ibm.com> Content-Type: text/plain Date: Wed, 30 May 2007 21:44:44 +1000 Message-Id: <1180525484.19517.266.camel@localhost.localdomain> Mime-Version: 1.0 Cc: linuxppc-dev list , Ulrich Weigand , Paul Mackerras , Steve Munroe , Anton Blanchard List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2007-05-30 at 00:32 -0500, Kumar Gala wrote: > > I think actually it would be useful to have the saving/restoring of > > the high 32 bits controlled by a prctl, so that programs have to ask > > explicitly for the new behaviour (and programs that don't want to > use > > the high 32 bits don't incur the extra overhead). > > I like this, it means we can error if HW doesn't support it and > requires applications to do something specific to enable the feature. Yeah well.... I liked the prctl at first.. but then, I though twice :-) Thing is, a typical usage pattern would be some library having a hand optimized tigh loop or something like that using 64 bits registers. An example, would be some memcpy-type thing in glibc. You don't want those things to do prctl's all over the place on behalf of the host application. Ben.