arch/x86_64/kernel/vsyscall.c

/*
 *  linux/arch/x86_64/kernel/vsyscall.c
 *
 *  Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE
 *
 *  Thanks to hpa@transmeta.com for some useful hint.
 *  Special thanks to Ingo Molnar for his early experience with
 *  a different vsyscall implementation for Linux/IA32 and for the name.
 *
 *  vsyscall 1 is located at -10Mbyte, vsyscall 2 is located
 *  at virtual address -10Mbyte+1024bytes etc... There are at max 8192
 *  vsyscalls. One vsyscall can reserve more than 1 slot to avoid
 *  jumping out of line if necessary.
 *
 *  $Id: vsyscall.c,v 1.26 2003/02/18 11:55:47 ak Exp $
 */

/*
 * TODO 2001-03-20:
 *
 * 1) make page fault handler detect faults on page1-page-last of the vsyscall
 *    virtual space, and make it increase %rip and write -ENOSYS in %rax (so
 *    we'll be able to upgrade to a new glibc without upgrading kernel after
 *    we add more vsyscalls.
 * 2) Possibly we need a fixmap table for the vsyscalls too if we want
 *    to avoid SIGSEGV and we want to return -EFAULT from the vsyscalls as well.
 *    Can we segfault inside a "syscall"? We can fix this anytime and those fixes
 *    won't be visible for userspace. Not fixing this is a noop for correct programs,
 *    broken programs will segfault and there's no security risk until we choose to
 *    fix it.
 *
 * These are not urgent things that we need to address only before shipping the first
 * production binary kernels.
 */

#include <linux/time.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/mm.h>

#include <asm/vsyscall.h>
#include <asm/pgtable.h>
#include <asm/page.h>
#include <asm/fixmap.h>
#include <asm/errno.h>
#include <asm/io.h>
#include <asm/msr.h>
#include <asm/unistd.h>

#define __vsyscall(nr) __attribute__ ((unused,__section__(".vsyscall_" #nr)))

#define force_inline inline __attribute__((always_inline))

long __vxtime_sequence[2] __section_vxtime_sequence;

static force_inline void do_vgettimeofday(struct timeval * tv)
{
	long sequence, t;
	unsigned long sec, usec;

	do {
		sequence = __vxtime_sequence[1];
		rmb();

		sec = __xtime.tv_sec;
		usec = __xtime.tv_usec + (__jiffies - __wall_jiffies) * (1000000 / HZ);

		switch (__vxtime.mode) {

			case VXTIME_TSC:
				sync_core();
				rdtscll(t);
				usec += (((t  - __vxtime.last_tsc) * __vxtime.tsc_quot) >> 32);
				break;

			case VXTIME_HPET:
				usec += ((readl(fix_to_virt(VSYSCALL_HPET) + 0xf0) - __vxtime.last) * __vxtime.quot) >> 32;
				break;

		}

		rmb();
	} while (sequence != __vxtime_sequence[0]);

	tv->tv_sec = sec + usec / 1000000;
	tv->tv_usec = usec % 1000000;
}


static force_inline void do_get_tz(struct timezone * tz)
{
	long sequence;

	do {
		sequence = __vxtime_sequence[1];
		rmb();

		*tz = __sys_tz;

		rmb();
	} while (sequence != __vxtime_sequence[0]);
}

static long __vsyscall(0) vgettimeofday(struct timeval * tv, struct timezone * tz)
{
	if (tv)
			do_vgettimeofday(tv);

	if (tz)
		do_get_tz(tz);

	return 0;
}

static time_t __vsyscall(1) vtime(time_t * tp)
{
	struct timeval tv;
	vgettimeofday(&tv, NULL);
	if (tp) *tp = tv.tv_sec;
	return tv.tv_sec;
}

static long __vsyscall(2) venosys_0(void)
{
	return -ENOSYS;
}

static long __vsyscall(3) venosys_1(void)
{
	return -ENOSYS;
}

extern char vsyscall_syscall[], __vsyscall_0[];

static void __init map_vsyscall(void)
{
	unsigned long physaddr_page0 = __pa_symbol(&__vsyscall_0);
	__set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_page0, PAGE_KERNEL_VSYSCALL);
	if (hpet_address)
		__set_fixmap(VSYSCALL_HPET, hpet_address, PAGE_KERNEL_VSYSCALL);
}

static int __init vsyscall_init(void)
{
	if ((unsigned long) &vgettimeofday != VSYSCALL_ADDR(__NR_vgettimeofday))
		panic("vgettimeofday link addr broken");
	if ((unsigned long) &vtime != VSYSCALL_ADDR(__NR_vtime))
		panic("vtime link addr broken");
	if (VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE))
		panic("fixmap first vsyscall %lx should be %lx", __fix_to_virt(VSYSCALL_FIRST_PAGE),
			VSYSCALL_ADDR(0));
	map_vsyscall();
	return 0;
}

__initcall(vsyscall_init);