From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161303AbXCBACF (ORCPT ); Thu, 1 Mar 2007 19:02:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161296AbXCBAB6 (ORCPT ); Thu, 1 Mar 2007 19:01:58 -0500 Received: from 207.47.60.4.static.nextweb.net ([207.47.60.4]:47894 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1161261AbXCAX4u (ORCPT ); Thu, 1 Mar 2007 18:56:50 -0500 Message-Id: <20070301232528.407996939@goop.org> References: <20070301232443.195603797@goop.org> User-Agent: quilt/0.46-1 Date: Thu, 01 Mar 2007 15:25:00 -0800 From: Jeremy Fitzhardinge To: Andi Kleen Cc: Andrew Morton , linux-kernel@vger.kernel.org, virtualization@lists.osdl.org, xen-devel@lists.xensource.com, Chris Wright , Zachary Amsden , Rusty Russell , Ian Pratt , Christian Limpach Subject: [patch 17/26] Xen-paravirt_ops: Add nosegneg capability to the vsyscall page notes Content-Disposition: inline; filename=xen-vsyscall-note.patch Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Add the "nosegneg" fake capabilty to the vsyscall page notes. This is used by the runtime linker to select a glibc version which then disables negative-offset accesses to the thread-local segment via %gs. These accesses require emulation in Xen (because segments are truncated to protect the hypervisor address space) and avoiding them provides a measurable performance boost. Signed-off-by: Ian Pratt Signed-off-by: Christian Limpach Signed-off-by: Chris Wright Acked-by: Zachary Amsden --- arch/i386/kernel/vsyscall-note.S | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) =================================================================== --- a/arch/i386/kernel/vsyscall-note.S +++ b/arch/i386/kernel/vsyscall-note.S @@ -23,3 +24,31 @@ 3: .balign 4; /* pad out section */ ASM_ELF_NOTE_BEGIN(".note.kernel-version", "a", UTS_SYSNAME, 0) .long LINUX_VERSION_CODE ASM_ELF_NOTE_END + +#ifdef CONFIG_XEN +/* + * Add a special note telling glibc's dynamic linker a fake hardware + * flavor that it will use to choose the search path for libraries in the + * same way it uses real hardware capabilities like "mmx". + * We supply "nosegneg" as the fake capability, to indicate that we + * do not like negative offsets in instructions using segment overrides, + * since we implement those inefficiently. This makes it possible to + * install libraries optimized to avoid those access patterns in someplace + * like /lib/i686/tls/nosegneg. Note that an /etc/ld.so.conf.d/file + * corresponding to the bits here is needed to make ldconfig work right. + * It should contain: + * hwcap 0 nosegneg + * to match the mapping of bit to name that we give here. + */ +#define NOTE_KERNELCAP_BEGIN(ncaps, mask) \ + ASM_ELF_NOTE_BEGIN(".note.kernelcap", "a", "GNU", 2) \ + .long ncaps, mask +#define NOTE_KERNELCAP(bit, name) \ + .byte bit; .asciz name +#define NOTE_KERNELCAP_END ASM_ELF_NOTE_END + +NOTE_KERNELCAP_BEGIN(1, 1) +NOTE_KERNELCAP(1, "nosegneg") +NOTE_KERNELCAP_END +#endif + --