elfnote.h

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#ifndef _LINUX_ELFNOTE_H
#define _LINUX_ELFNOTE_H
/*
 * Helper macros to generate ELF Note structures, which are put into a
 * PT_NOTE segment of the final vmlinux image.  These are useful for
 * including name-value pairs of metadata into the kernel binary (or
 * modules?) for use by external programs.
 *
 * Each note has three parts: a name, a type and a desc.  The name is
 * intended to distinguish the note's originator, so it would be a
 * company, project, subsystem, etc; it must be in a suitable form for
 * use in a section name.  The type is an integer which is used to tag
 * the data, and is considered to be within the "name" namespace (so
 * "FooCo"'s type 42 is distinct from "BarProj"'s type 42).  The
 * "desc" field is the actual data.  There are no constraints on the
 * desc field's contents, though typically they're fairly small.
 *
 * All notes from a given NAME are put into a section named
 * .note.NAME.  When the kernel image is finally linked, all the notes
 * are packed into a single .notes section, which is mapped into the
 * PT_NOTE segment.  Because notes for a given name are grouped into
 * the same section, they'll all be adjacent the output file.
 *
 * This file defines macros for both C and assembler use.  Their
 * syntax is slightly different, but they're semantically similar.
 *
 * See the ELF specification for more detail about ELF notes.
 */

#ifdef __ASSEMBLER__
/*
 * Generate a structure with the same shape as Elf{32,64}_Nhdr (which
 * turn out to be the same size and shape), followed by the name and
 * desc data with appropriate padding.  The 'desctype' argument is the
 * assembler pseudo op defining the type of the data e.g. .asciz while
 * 'descdata' is the data itself e.g.  "hello, world".
 *
 * e.g. ELFNOTE(XYZCo, 42, .asciz, "forty-two")
 *      ELFNOTE(XYZCo, 12, .long, 0xdeadbeef)
 */
#define ELFNOTE_START(name, type, flags)    \
.pushsection .note.name, flags,@note    ;   \
  .balign 4             ;   \
  .long 2f - 1f     /* namesz */    ;   \
  .long 4484f - 3f  /* descsz */    ;   \
  .long type                ;   \
1:.asciz #name              ;   \
2:.balign 4             ;   \
3:

#define ELFNOTE_END             \
4484:.balign 4              ;   \
.popsection             ;

#define ELFNOTE(name, type, desc)       \
    ELFNOTE_START(name, type, "")       \
        desc            ;   \
    ELFNOTE_END

#else   /* !__ASSEMBLER__ */
#include <linux/elf.h>
/*
 * Use an anonymous structure which matches the shape of
 * Elf{32,64}_Nhdr, but includes the name and desc data.  The size and
 * type of name and desc depend on the macro arguments.  "name" must
 * be a literal string, and "desc" must be passed by value.  You may
 * only define one note per line, since __LINE__ is used to generate
 * unique symbols.
 */
#define _ELFNOTE_PASTE(a,b) a##b
#define _ELFNOTE(size, name, unique, type, desc)            \
    static const struct {                       \
        struct elf##size##_note _nhdr;              \
        unsigned char _name[sizeof(name)]           \
        __attribute__((aligned(sizeof(Elf##size##_Word)))); \
        typeof(desc) _desc                  \
                 __attribute__((aligned(sizeof(Elf##size##_Word)))); \
    } _ELFNOTE_PASTE(_note_, unique)                \
        __used                          \
        __attribute__((section(".note." name),          \
                   aligned(sizeof(Elf##size##_Word)),   \
                   unused)) = {             \
        {                           \
            sizeof(name),                   \
            sizeof(desc),                   \
            type,                       \
        },                          \
        name,                           \
        desc                            \
    }
#define ELFNOTE(size, name, type, desc)     \
    _ELFNOTE(size, name, __LINE__, type, desc)

#define ELFNOTE32(name, type, desc) ELFNOTE(32, name, type, desc)
#define ELFNOTE64(name, type, desc) ELFNOTE(64, name, type, desc)
#endif  /* __ASSEMBLER__ */

#endif /* _LINUX_ELFNOTE_H */