/* * vvar.h: Shared vDSO/kernel variable declarations * Copyright (c) 2011 Andy Lutomirski * Subject to the GNU General Public License, version 2 * * A handful of variables are accessible (read-only) from userspace * code in the vsyscall page and the vdso. They are declared here. * Some other file must define them with DEFINE_VVAR. * * In normal kernel code, they are used like any other variable. * In user code, they are accessed through the VVAR macro. * * These variables live in a page of kernel data that has an extra RO * mapping for userspace. Each variable needs a unique offset within * that page; specify that offset with the DECLARE_VVAR macro. (If * you mess up, the linker will catch it.) */ #ifndef _ASM_X86_VVAR_H #define _ASM_X86_VVAR_H #if defined(__VVAR_KERNEL_LDS) /* The kernel linker script defines its own magic to put vvars in the * right place. */ #define DECLARE_VVAR(offset, type, name) \ EMIT_VVAR(name, offset) #else extern char __vvar_page; #define DECLARE_VVAR(offset, type, name) \ extern type vvar_ ## name __attribute__((visibility("hidden"))); #define VVAR(name) (vvar_ ## name) #define DEFINE_VVAR(type, name) \ type name \ __attribute__((section(".vvar_" #name), aligned(16))) __visible #endif /* DECLARE_VVAR(offset, type, name) */ DECLARE_VVAR(128, struct vsyscall_gtod_data, vsyscall_gtod_data) #undef DECLARE_VVAR #endif