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 028D7DDEC5 for ; Wed, 30 May 2007 22:15:55 +1000 (EST) In-Reply-To: <1180525484.19517.266.camel@localhost.localdomain> References: <18012.61822.197988.279764@cargo.ozlabs.ibm.com> <1180525484.19517.266.camel@localhost.localdomain> Mime-Version: 1.0 (Apple Message framework v752.2) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: <91D21C34-3D3C-4A1F-9B2E-08F336B7EFC4@kernel.crashing.org> From: Kumar Gala Subject: Re: Saving to 32 bits of GPRs in signal context Date: Wed, 30 May 2007 07:15:46 -0500 To: Benjamin Herrenschmidt 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 May 30, 2007, at 6:44 AM, Benjamin Herrenschmidt wrote: > 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. Yeah, I can see that being a pain. However, how would the AT_HWCAP make this any easier on the library to detect? (I might have missed that discussion of that magic in the thread). - k