The patch titled
xen-paravirt_ops: add nosegneg capability to the vsyscall page notes
has been removed from the -mm tree. Its filename was
xen-paravirt_ops-add-nosegneg-capability-to-the-vsyscall-page-notes.patch
This patch was dropped because Zach's patches destroyed it all
------------------------------------------------------
Subject: xen-paravirt_ops: add nosegneg capability to the vsyscall page notes
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
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@xxxxxxxxxxxxx>
Signed-off-by: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
Acked-by: Zachary Amsden <zach@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/i386/kernel/vsyscall-note.S | 28 ++++++++++++++++++++++++++++
1 files changed, 28 insertions(+)
diff -puN arch/i386/kernel/vsyscall-note.S~xen-paravirt_ops-add-nosegneg-capability-to-the-vsyscall-page-notes arch/i386/kernel/vsyscall-note.S
--- a/arch/i386/kernel/vsyscall-note.S~xen-paravirt_ops-add-nosegneg-capability-to-the-vsyscall-page-notes
+++ a/arch/i386/kernel/vsyscall-note.S
@@ -23,3 +23,31 @@
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
+
_
Patches currently in -mm which might be from jeremy@xxxxxxxx are
xen-paravirt_ops-add-nosegneg-capability-to-the-vsyscall-page-notes.patch
xen-paravirt_ops-add-xen-config-options.patch
xen-paravirt_ops-add-xen-interface-header-files.patch
xen-paravirt_ops-core-xen-implementation.patch
xen-paravirt_ops-use-the-hvc-console-infrastructure-for-xen-console.patch
xen-paravirt_ops-add-early-printk-support-via-hvc-console.patch
xen-paravirt_ops-add-xen-grant-table-support.patch
xen-paravirt_ops-add-the-xenbus-sysfs-and-virtual-device-hotplug-driver.patch
xen-paravirt_ops-add-xen-virtual-block-device-driver.patch
xen-paravirt_ops-add-the-xen-virtual-network-device-driver.patch
fixes-and-cleanups-for-earlyprintk-aka-boot-console.patch
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