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 */