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 32extern 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 47DECLARE_VVAR(128, struct vsyscall_gtod_data, vsyscall_gtod_data) 48 49#undef DECLARE_VVAR 50 51#endif 52