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 |
52 | |