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 #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 */ 97