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