elfnote.h

 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				;	\
481:.asciz #name				;	\
492:.balign 4				;	\
503:
51
52#define ELFNOTE_END				\
534484:.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#include <linux/compiler.h>
64/*
65 * Use an anonymous structure which matches the shape of
66 * Elf{32,64}_Nhdr, but includes the name and desc data.  The size and
67 * type of name and desc depend on the macro arguments.  "name" must
68 * be a literal string, and "desc" must be passed by value.
69 */
70#define ELFNOTE(size, name, type, desc)					\
71	static const struct {						\
72		struct elf##size##_note _nhdr;				\
73		unsigned char _name[sizeof(name)]			\
74		__attribute__((aligned(sizeof(Elf##size##_Word))));	\
75		typeof(desc) _desc					\
76			     __attribute__((aligned(sizeof(Elf##size##_Word)))); \
77	} __UNIQUE_ID(note)						\
78		__used							\
79		__attribute__((section(".note." name),			\
80			       aligned(sizeof(Elf##size##_Word)),	\
81			       unused)) = {				\
82		{							\
83			sizeof(name),					\
84			sizeof(desc),					\
85			type,						\
86		},							\
87		name,							\
88		desc							\
89	}
90
91#define ELFNOTE32(name, type, desc) ELFNOTE(32, name, type, desc)
92#define ELFNOTE64(name, type, desc) ELFNOTE(64, name, type, desc)
93
94#endif	/* __ASSEMBLER__ */
95
96#endif /* _LINUX_ELFNOTE_H */