From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754480AbXDWXNz (ORCPT ); Mon, 23 Apr 2007 19:13:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753354AbXDWXNk (ORCPT ); Mon, 23 Apr 2007 19:13:40 -0400 Received: from 61.sub-75-208-107.myvzw.com ([75.208.107.61]:38871 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932812AbXDWXHi (ORCPT ); Mon, 23 Apr 2007 19:07:38 -0400 Message-Id: <20070423215709.802499615@goop.org> References: <20070423215638.563901986@goop.org> User-Agent: quilt/0.46-1 Date: Mon, 23 Apr 2007 14:56:41 -0700 From: Jeremy Fitzhardinge To: Andi Kleen Cc: Andrew Morton , virtualization@lists.osdl.org, lkml , Ian Pratt , Christian Limpach , Chris Wright , Zachary Amsden , Roland McGrath , Ulrich Drepper Subject: [PATCH 03/25] xen: 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 Signed-off-by: Jeremy Fitzhardinge Acked-by: Zachary Amsden Cc: Roland McGrath Cc: Ulrich Drepper --- 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, 2) +NOTE_KERNELCAP(1, "nosegneg") +NOTE_KERNELCAP_END +#endif + --