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 */