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#ifdef EMIT_VVAR
23/*
24 * EMIT_VVAR() is used by the kernel linker script to put vvars in the
25 * right place. Also, it's used by kernel code to import offsets values.
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 extern type timens_ ## name[CS_BASES] \
38 __attribute__((visibility("hidden"))); \
39
40#define VVAR(name) (vvar_ ## name)
41#define TIMENS(name) (timens_ ## name)
42
43#define DEFINE_VVAR(type, name) \
44 type name[CS_BASES] \
45 __attribute__((section(".vvar_" #name), aligned(16))) __visible
46
47#endif
48
49/* DECLARE_VVAR(offset, type, name) */
50
51DECLARE_VVAR(128, struct vdso_data, _vdso_data)
52
53#undef DECLARE_VVAR
54
55#endif
56

source code of linux/arch/x86/include/asm/vvar.h