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))) __visible
  39
  40 #define VVAR(name) (*vvaraddr_ ## name)
  41
  42 #endif
  43
  44 /* DECLARE_VVAR(offset, type, name) */
  45
  46 DECLARE_VVAR(0, volatile unsigned long, jiffies)
  47 DECLARE_VVAR(16, int, vgetcpu_mode)
  48 DECLARE_VVAR(128, struct vsyscall_gtod_data, vsyscall_gtod_data)
  49
  50 #undef DECLARE_VVAR