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
32 extern 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
48 DECLARE_VVAR(128, struct vdso_data, _vdso_data)
49
50 #undef DECLARE_VVAR
51
52 #endif