LXR linux/arch/x86/include/asm/vvar.h

   1/*
   2 * vvar.h: Shared vDSO/kernel variable declarations
   3 * Copyright (c) 2011 Andy Lutomirski
   4 * Subject to the GNU General Public License, version 2
   5 *
   6 * A handful of variables are accessible (read-only) from userspace
   7 * code in the vsyscall page and the vdso.  They are declared here.
   8 * Some other file must define them with DEFINE_VVAR.
   9 *
  10 * In normal kernel code, they are used like any other variable.
  11 * In user code, they are accessed through the VVAR macro.
  12 *
  13 * These variables live in a page of kernel data that has an extra RO
  14 * mapping for userspace.  Each variable needs a unique offset within
  15 * that page; specify that offset with the DECLARE_VVAR macro.  (If
  16 * you mess up, the linker will catch it.)
  17 */
  18
  19/* Base address of vvars.  This is not ABI. */
  20#define VVAR_ADDRESS (-10*1024*1024 - 4096)
  21
  22#if defined(__VVAR_KERNEL_LDS)
  23
  24/* The kernel linker script defines its own magic to put vvars in the
  25 * right place.
  26 */
  27#define DECLARE_VVAR(offset, type, name) \
  28        EMIT_VVAR(name, offset)
  29
  30#else
  31
  32#define DECLARE_VVAR(offset, type, name)                                \
  33        static type const * const vvaraddr_ ## name =                   \
  34                (void *)(VVAR_ADDRESS + (offset));
  35
  36#define DEFINE_VVAR(type, name)                                         \
  37        type name                                                       \
  38        __attribute__((section(".vvar_" #name), aligned(16)))
  39
  40#define VVAR(name) (*vvaraddr_ ## name)
  41
  42#endif
  43
  44/* DECLARE_VVAR(offset, type, name) */
  45
  46DECLARE_VVAR(0, volatile unsigned long, jiffies)
  47DECLARE_VVAR(16, int, vgetcpu_mode)
  48DECLARE_VVAR(128, struct vsyscall_gtod_data, vsyscall_gtod_data)
  49
  50#undef DECLARE_VVAR
  51