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linux-next/arch/x86/vdso/vvar.c

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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>
2007-07-21 23:10:01 +08:00
/* Define pointer to external vDSO variables.
These are part of the vDSO. The kernel fills in the real addresses
at boot time. This is done because when the vdso is linked the
kernel isn't yet and we don't know the final addresses. */
#include <linux/kernel.h>
#include <linux/time.h>
#include <asm/vsyscall.h>
#include <asm/timex.h>
#include <asm/vgtod.h>
x86: vdso put vars in rodata This adds a const to the definitions vvar.c makes, so that the vdso_* variables go into .rodata instead of .data. This is essentially a cosmetic change, just giving the section headers in the vDSO file more pleasing flags. These variables are read-only from the perspective of the vDSO itself and user mode, even though the contents of the DSO image were adjusted at boot. Signed-off-by: Roland McGrath <roland@redhat.com> Cc: Andi Kleen <ak@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2007-10-18 00:04:40 +08:00
#define VEXTERN(x) typeof (__ ## x) *const vdso_ ## x = (void *)VMAGIC;
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>
2007-07-21 23:10:01 +08:00
#include "vextern.h"
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