include/linux/elfnote.h

   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, "")           \
  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 */