From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robert Jarzmik Subject: Re: [PATCH 2/3] ARM: convert to generated system call tables Date: Sat, 22 Oct 2016 22:23:54 +0200 Message-ID: <87eg382kv9.fsf@belgarion.home> References: <4337157.Eff9E2riVH@wuerfel> <20161021154856.GC1041@n2100.armlinux.org.uk> <24632117.YsmPs86ri6@wuerfel> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <24632117.YsmPs86ri6@wuerfel> (Arnd Bergmann's message of "Fri, 21 Oct 2016 22:35:53 +0200") Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Arnd Bergmann Cc: Russell King - ARM Linux , linux-arch , linux-api , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: linux-arch.vger.kernel.org Arnd Bergmann writes: > On Friday, October 21, 2016 4:48:56 PM CEST Russell King - ARM Linux wrote: >> What's the point of the x32 mode? > > On x86, the motivation is faster code for most use cases that > don't need a lot of memory, as the 64-bit opcodes have 16 registers > rather than 8 in 32-bit mode but 32-bit pointers have lower > cache footprint than 64-bit pointers. For completness, the second point of x32 AFAIU is the IP-relative addressing which is not available in standard 32 bit mode, which improves PIC code. For simple not algorithmic code (think Android HAL for example) with many shared libraries, it's better in the Hardware Abstraction Layer Libraries, instead of the push-to-stack and pop register. Cheers. -- Robert From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp07.smtpout.orange.fr ([80.12.242.129]:23700 "EHLO smtp.smtpout.orange.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752134AbcJVUX7 (ORCPT ); Sat, 22 Oct 2016 16:23:59 -0400 From: Robert Jarzmik Subject: Re: [PATCH 2/3] ARM: convert to generated system call tables References: <4337157.Eff9E2riVH@wuerfel> <20161021154856.GC1041@n2100.armlinux.org.uk> <24632117.YsmPs86ri6@wuerfel> Date: Sat, 22 Oct 2016 22:23:54 +0200 In-Reply-To: <24632117.YsmPs86ri6@wuerfel> (Arnd Bergmann's message of "Fri, 21 Oct 2016 22:35:53 +0200") Message-ID: <87eg382kv9.fsf@belgarion.home> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-arch-owner@vger.kernel.org List-ID: To: Arnd Bergmann Cc: Russell King - ARM Linux , linux-arch , linux-api , linux-arm-kernel@lists.infradead.org Message-ID: <20161022202354.XQFAXQoYkrLkQhSGoVEUxZYszSVD92P0O_3eXUMEo7o@z> Arnd Bergmann writes: > On Friday, October 21, 2016 4:48:56 PM CEST Russell King - ARM Linux wrote: >> What's the point of the x32 mode? > > On x86, the motivation is faster code for most use cases that > don't need a lot of memory, as the 64-bit opcodes have 16 registers > rather than 8 in 32-bit mode but 32-bit pointers have lower > cache footprint than 64-bit pointers. For completness, the second point of x32 AFAIU is the IP-relative addressing which is not available in standard 32 bit mode, which improves PIC code. For simple not algorithmic code (think Android HAL for example) with many shared libraries, it's better in the Hardware Abstraction Layer Libraries, instead of the push-to-stack and pop register. Cheers. -- Robert