From 2aae950b21e4bc789d1fc6668faf67e8748300b7 Mon Sep 17 00:00:00 2001
From: Andi Kleen <ak@suse.de>
Date: Sat, 21 Jul 2007 17:10:01 +0200
Subject: x86_64: Add vDSO for x86-64 with gettimeofday/clock_gettime/getcpu
This implements new vDSO for x86-64. The concept is similar
to the existing vDSOs on i386 and PPC. x86-64 has had static
vsyscalls before, but these are not flexible enough anymore.
A vDSO is a ELF shared library supplied by the kernel that is mapped into
user address space. The vDSO mapping is randomized for each process
for security reasons.
Doing this was needed for clock_gettime, because clock_gettime
always needs a syscall fallback and having one at a fixed
address would have made buffer overflow exploits too easy to write.
The vdso can be disabled with vdso=0
It currently includes a new gettimeofday implemention and optimized
clock_gettime(). The gettimeofday implementation is slightly faster
than the one in the old vsyscall. clock_gettime is significantly faster
than the syscall for CLOCK_MONOTONIC and CLOCK_REALTIME.
The new calls are generally faster than the old vsyscall.
Advantages over the old x86-64 vsyscalls:
- Extensible
- Randomized
- Cleaner
- Easier to virtualize (the old static address range previously causes
overhead e.g. for Xen because it has to create special page tables for it)
Weak points:
- glibc support still to be written
The VM interface is partly based on Ingo Molnar's i386 version.
Includes compile fix from Joachim Deguara
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
arch/x86_64/vdso/vextern.h | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
create mode 100644 arch/x86_64/vdso/vextern.h
(limited to 'arch/x86_64/vdso/vextern.h')
diff --git a/arch/x86_64/vdso/vextern.h b/arch/x86_64/vdso/vextern.h
new file mode 100644
index 000000000000..1683ba2ae3e8
--- /dev/null
+++ b/arch/x86_64/vdso/vextern.h
@@ -0,0 +1,16 @@
+#ifndef VEXTERN
+#include <asm/vsyscall.h>
+#define VEXTERN(x) \
+ extern typeof(x) *vdso_ ## x __attribute__((visibility("hidden")));
+#endif
+
+#define VMAGIC 0xfeedbabeabcdefabUL
+
+/* Any kernel variables used in the vDSO must be exported in the main
+ kernel's vmlinux.lds.S/vsyscall.h/proper __section and
+ put into vextern.h and be referenced as a pointer with vdso prefix.
+ The main kernel later fills in the values. */
+
+VEXTERN(jiffies)
+VEXTERN(vgetcpu_mode)
+VEXTERN(vsyscall_gtod_data)
--
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