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From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Andrew Morton <akpm@osdl.org>
Cc: linux-kernel@vger.kernel.org, virtualization@lists.osdl.org,
	xen-devel@lists.xensource.com,
	Ian Pratt <ian.pratt@xensource.com>,
	Christian Limpach <Christian.Limpach@cl.cam.ac.uk>,
	Chris Wright <chrisw@sous-sol.org>
Subject: [patch 12/20] XEN-paravirt: Xen: Add nosegneg capability to the vsyscall page notes
Date: Fri, 12 Jan 2007 17:45:51 -0800	[thread overview]
Message-ID: <20070113014648.311911321@goop.org> (raw)
In-Reply-To: <20070113014539.408244126@goop.org>

[-- Attachment #1: xen-vsyscall-note.patch --]
[-- Type: text/plain, Size: 2072 bytes --]

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 <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
 arch/i386/kernel/vsyscall-note.S |   29 +++++++++++++++++++++++++++++
 1 files changed, 29 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
+

-- 


  parent reply	other threads:[~2007-01-13 23:11 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-13  1:45 [patch 00/20] XEN-paravirt: Xen guest implementation for paravirt_ops interface Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 01/20] XEN-paravirt: Fix typo in sync_constant_test_bit()s name Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 02/20] XEN-paravirt: Add a flag to allow the VGA console to be disabled Jeremy Fitzhardinge
2007-01-14  0:27   ` [Xen-devel] " Alan
2007-01-13  1:45 ` [patch 03/20] XEN-paravirt: paravirt: page-table accessors Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 04/20] XEN-paravirt: paravirt pagetable init Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 05/20] XEN-paravirt: paravirt: reserve fixmap slot Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 06/20] XEN-paravirt: remove pgd ctor Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 07/20] XEN-paravirt: paravirt shared kernel pmd flag Jeremy Fitzhardinge
2007-01-15  8:59   ` [Xen-devel] " Jan Beulich
2007-01-13  1:45 ` [patch 08/20] XEN-paravirt: paravirt pgd allocation alignment Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 09/20] XEN-paravirt: dont export paravirt_ops structure, do individual functions Jeremy Fitzhardinge
2007-01-14  0:57   ` Rusty Russell
2007-01-13  1:45 ` [patch 10/20] XEN-paravirt: mm lifetime hooks Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 11/20] XEN-paravirt: Add apply_to_page_range() which applies a function to a pte range Jeremy Fitzhardinge
2007-01-13  1:45 ` Jeremy Fitzhardinge [this message]
2007-01-13  1:45 ` [patch 13/20] XEN-paravirt: Xen: Add config options and disable unsupported config options Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 15/20] XEN-paravirt: Xen: core paravirt guest changes Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 16/20] XEN-paravirt: Add the Xen virtual console driver Jeremy Fitzhardinge
2007-01-14  0:37   ` Alan
2007-01-14  0:35     ` Jeremy Fitzhardinge
2007-01-15 13:03   ` Pavel Machek
2007-01-19  4:11     ` Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 17/20] XEN-paravirt: Add Xen grant table support Jeremy Fitzhardinge
2007-01-15 13:05   ` Pavel Machek
2007-01-19  4:07     ` Jeremy Fitzhardinge
2007-01-13  1:45 ` [patch 18/20] XEN-paravirt: Add Xen driver utility functions Jeremy Fitzhardinge
2007-01-14  7:41   ` Greg KH
2007-01-13  1:45 ` [patch 19/20] XEN-paravirt: Add the Xenbus sysfs and virtual device hotplug driver Jeremy Fitzhardinge
2007-01-15 13:18   ` Pavel Machek
2007-01-13  1:45 ` [patch 20/20] XEN-paravirt: Add Xen virtual block device driver Jeremy Fitzhardinge
2007-01-14  1:07   ` Arjan van de Ven
2007-01-14  7:43     ` Greg KH
2007-01-16  2:53     ` [Xen-devel] " Mark Williamson
2007-01-14 11:05   ` Jan Engelhardt
2007-01-14 11:24     ` Muli Ben-Yehuda
2007-01-14 11:35       ` Jan Engelhardt
2007-01-14 12:37     ` Keir Fraser

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