1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_ELFNOTE_H
3 #define _LINUX_ELFNOTE_H
4 /*
5  * Helper macros to generate ELF Note structures, which are put into a
6  * PT_NOTE segment of the final vmlinux image.  These are useful for
7  * including name-value pairs of metadata into the kernel binary (or
8  * modules?) for use by external programs.
9  *
10  * Each note has three parts: a name, a type and a desc.  The name is
11  * intended to distinguish the note's originator, so it would be a
12  * company, project, subsystem, etc; it must be in a suitable form for
13  * use in a section name.  The type is an integer which is used to tag
14  * the data, and is considered to be within the "name" namespace (so
15  * "FooCo"'s type 42 is distinct from "BarProj"'s type 42).  The
16  * "desc" field is the actual data.  There are no constraints on the
17  * desc field's contents, though typically they're fairly small.
18  *
19  * All notes from a given NAME are put into a section named
20  * .note.NAME.  When the kernel image is finally linked, all the notes
21  * are packed into a single .notes section, which is mapped into the
22  * PT_NOTE segment.  Because notes for a given name are grouped into
23  * the same section, they'll all be adjacent the output file.
24  *
25  * This file defines macros for both C and assembler use.  Their
26  * syntax is slightly different, but they're semantically similar.
27  *
28  * See the ELF specification for more detail about ELF notes.
29  */
30 
31 #ifdef __ASSEMBLER__
32 /*
33  * Generate a structure with the same shape as Elf{32,64}_Nhdr (which
34  * turn out to be the same size and shape), followed by the name and
35  * desc data with appropriate padding.  The 'desctype' argument is the
36  * assembler pseudo op defining the type of the data e.g. .asciz while
37  * 'descdata' is the data itself e.g.  "hello, world".
38  *
39  * e.g. ELFNOTE(XYZCo, 42, .asciz, "forty-two")
40  *      ELFNOTE(XYZCo, 12, .long, 0xdeadbeef)
41  */
42 #define ELFNOTE_START(name, type, flags)	\
43 .pushsection .note.name, flags,@note	;	\
44   .balign 4				;	\
45   .long 2f - 1f		/* namesz */	;	\
46   .long 4484f - 3f	/* descsz */	;	\
47   .long type				;	\
48 1:.asciz #name				;	\
49 2:.balign 4				;	\
50 3:
51 
52 #define ELFNOTE_END				\
53 4484:.balign 4				;	\
54 .popsection				;
55 
56 #define ELFNOTE(name, type, desc)		\
57 	ELFNOTE_START(name, type, "a")		\
58 		desc			;	\
59 	ELFNOTE_END
60 
61 #else	/* !__ASSEMBLER__ */
62 #include <linux/elf.h>
63 /*
64  * Use an anonymous structure which matches the shape of
65  * Elf{32,64}_Nhdr, but includes the name and desc data.  The size and
66  * type of name and desc depend on the macro arguments.  "name" must
67  * be a literal string, and "desc" must be passed by value.  You may
68  * only define one note per line, since __LINE__ is used to generate
69  * unique symbols.
70  */
71 #define _ELFNOTE_PASTE(a,b)	a##b
72 #define _ELFNOTE(size, name, unique, type, desc)			\
73 	static const struct {						\
74 		struct elf##size##_note _nhdr;				\
75 		unsigned char _name[sizeof(name)]			\
76 		__attribute__((aligned(sizeof(Elf##size##_Word))));	\
77 		typeof(desc) _desc					\
78 			     __attribute__((aligned(sizeof(Elf##size##_Word)))); \
79 	} _ELFNOTE_PASTE(_note_, unique)				\
80 		__used							\
81 		__attribute__((section(".note." name),			\
82 			       aligned(sizeof(Elf##size##_Word)),	\
83 			       unused)) = {				\
84 		{							\
85 			sizeof(name),					\
86 			sizeof(desc),					\
87 			type,						\
88 		},							\
89 		name,							\
90 		desc							\
91 	}
92 #define ELFNOTE(size, name, type, desc)		\
93 	_ELFNOTE(size, name, __LINE__, type, desc)
94 
95 #define ELFNOTE32(name, type, desc) ELFNOTE(32, name, type, desc)
96 #define ELFNOTE64(name, type, desc) ELFNOTE(64, name, type, desc)
97 #endif	/* __ASSEMBLER__ */
98 
99 #endif /* _LINUX_ELFNOTE_H */
100