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 #ifndef _ASM_X86_VVAR_H
  20 #define _ASM_X86_VVAR_H
  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 extern char __vvar_page;
  33
  34 #define DECLARE_VVAR(offset, type, name)                                \
  35         extern type vvar_ ## name __attribute__((visibility("hidden")));
  36
  37 #define VVAR(name) (vvar_ ## name)
  38
  39 #define DEFINE_VVAR(type, name)                                         \
  40         type name                                                       \
  41         __attribute__((section(".vvar_" #name), aligned(16))) __visible
  42
  43 #endif
  44
  45 /* DECLARE_VVAR(offset, type, name) */
  46
  47 DECLARE_VVAR(128, struct vsyscall_gtod_data, vsyscall_gtod_data)
  48
  49 #undef DECLARE_VVAR
  50
  51 #endif