include/asm/vvar.h

0001 /* SPDX-License-Identifier: GPL-2.0-only */
0002 /*
0003  * vvar.h: Shared vDSO/kernel variable declarations
0004  * Copyright (c) 2011 Andy Lutomirski
0005  *
0006  * A handful of variables are accessible (read-only) from userspace
0007  * code in the vsyscall page and the vdso.  They are declared here.
0008  * Some other file must define them with DEFINE_VVAR.
0009  *
0010  * In normal kernel code, they are used like any other variable.
0011  * In user code, they are accessed through the VVAR macro.
0012  *
0013  * These variables live in a page of kernel data that has an extra RO
0014  * mapping for userspace.  Each variable needs a unique offset within
0015  * that page; specify that offset with the DECLARE_VVAR macro.  (If
0016  * you mess up, the linker will catch it.)
0017  */
0018
0019 #ifndef _ASM_X86_VVAR_H
0020 #define _ASM_X86_VVAR_H
0021
0022 #ifdef EMIT_VVAR
0023 /*
0024  * EMIT_VVAR() is used by the kernel linker script to put vvars in the
0025  * right place. Also, it's used by kernel code to import offsets values.
0026  */
0027 #define DECLARE_VVAR(offset, type, name) \
0028     EMIT_VVAR(name, offset)
0029
0030 #else
0031
0032 extern char __vvar_page;
0033
0034 #define DECLARE_VVAR(offset, type, name)                \
0035     extern type vvar_ ## name[CS_BASES]             \
0036     __attribute__((visibility("hidden")));              \
0037     extern type timens_ ## name[CS_BASES]               \
0038     __attribute__((visibility("hidden")));              \
0039
0040 #define VVAR(name) (vvar_ ## name)
0041 #define TIMENS(name) (timens_ ## name)
0042
0043 #define DEFINE_VVAR(type, name)                     \
0044     type name[CS_BASES]                     \
0045     __attribute__((section(".vvar_" #name), aligned(16))) __visible
0046
0047 #endif
0048
0049 /* DECLARE_VVAR(offset, type, name) */
0050
0051 DECLARE_VVAR(128, struct vdso_data, _vdso_data)
0052
0053 #undef DECLARE_VVAR
0054
0055 #endif