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 <uapi/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