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

   1/* SPDX-License-Identifier: GPL-2.0-only */
   2/*
   3 * vvar.h: Shared vDSO/kernel variable declarations
   4 * Copyright (c) 2011 Andy Lutomirski
   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
  32extern char __vvar_page;
  33
  34#define DECLARE_VVAR(offset, type, name)                                \
  35        extern type vvar_ ## name[CS_BASES]                             \
  36        __attribute__((visibility("hidden")));
  37
  38#define VVAR(name) (vvar_ ## name)
  39
  40#define DEFINE_VVAR(type, name)                                         \
  41        type name[CS_BASES]                                             \
  42        __attribute__((section(".vvar_" #name), aligned(16))) __visible
  43
  44#endif
  45
  46/* DECLARE_VVAR(offset, type, name) */
  47
  48DECLARE_VVAR(128, struct vdso_data, _vdso_data)
  49
  50#undef DECLARE_VVAR
  51
  52#endif
  53