Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750904AbWCVGht (ORCPT ); Wed, 22 Mar 2006 01:37:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750896AbWCVGht (ORCPT ); Wed, 22 Mar 2006 01:37:49 -0500 Received: from 216-99-217-87.dsl.aracnet.com ([216.99.217.87]:10371 "EHLO sorel.sous-sol.org") by vger.kernel.org with ESMTP id S1750891AbWCVGhr (ORCPT ); Wed, 22 Mar 2006 01:37:47 -0500 Message-Id: <20060322063802.797884000@sorel.sous-sol.org> References: <20060322063040.960068000@sorel.sous-sol.org> Date: Tue, 21 Mar 2006 22:31:07 -0800 From: Chris Wright To: linux-kernel@vger.kernel.org Cc: xen-devel@lists.xensource.com, virtualization@lists.osdl.org, Ian Pratt , Christian Limpach Subject: [RFC PATCH 27/35] Add nosegneg capability to the vsyscall page notes Content-Disposition: inline; filename=26-i386-vsyscall-note Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2402 Lines: 63 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 --- arch/i386/kernel/vsyscall-note.S | 29 +++++++++++++++++++++++++++++ 1 files changed, 29 insertions(+) --- xen-subarch-2.6.orig/arch/i386/kernel/vsyscall-note.S +++ xen-subarch-2.6/arch/i386/kernel/vsyscall-note.S @@ -3,6 +3,7 @@ * Here we can supply some information useful to userland. */ +#include #include #include @@ -23,3 +24,31 @@ 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 + -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/