Linux Kernel  3.7.1
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vvar.h
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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 /* Base address of vvars. This is not ABI. */
20 #define VVAR_ADDRESS (-10*1024*1024 - 4096)
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 #define DECLARE_VVAR(offset, type, name) \
33  static type const * const vvaraddr_ ## name = \
34  (void *)(VVAR_ADDRESS + (offset));
35 
36 #define DEFINE_VVAR(type, name) \
37  type name \
38  __attribute__((section(".vvar_" #name), aligned(16)))
39 
40 #define VVAR(name) (*vvaraddr_ ## name)
41 
42 #endif
43 
44 /* DECLARE_VVAR(offset, type, name) */
45 
46 DECLARE_VVAR(0, volatile unsigned long, jiffies)
47 DECLARE_VVAR(16, int, vgetcpu_mode)
48 DECLARE_VVAR(128, struct vsyscall_gtod_data, vsyscall_gtod_data)
49 
50 #undef DECLARE_VVAR