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  ,   	ˆl—Ðz¾”ªe¶…6 ¸Ë7mLZ7ÿÀƒ}±;_‡I|¥ŠèªÅÄ %7    	# copyright : Copyright (c) 2017-2024 Red Hat
# license   : GNU GFDL v1.3; see accompanying LICENSE file.

       Storing Build Time Information In ELF Binary Files
	    In a Format Suitable for Static Analysis

  A specification by Nick Clifton.  Version 3.0.  Dec 20, 2017.

ChangeLog:
  For v3.0:
    Add end-of-range addresses to description field, to allow
    for gaps in the coverage.

  For v2.0:
    Added an "owner" string at the start of the name field so that
    naive processors of Elf Notes are less likely to complain. 

----------------------------------------------------------------------

* The information is stored in a new section in the file using the ELF
  NOTE format.  This format is already well defined, and supported by
  binary tools.

  Creator tools (compilers, assemblers) place the notes into the
  binary files.  Consumer tools (readelf, built-by) read the notes and
  answer questions  about the binaries concerned.  Processing tools
  (linker, objcopy) combine and merge the notes as needed.

  Note - this specification could have used the gnu_attributes format
  instead, but this has a few drawbacks:

  - Support for section and symbol tagged gnu_attributes is not
    currently implemented anywhere, and these features are needed.
    Adding support for them to the binutils would mean that the
    specification is not backwards compatible with older tools.

  * The gnu attributes specification requires that when merging
    attributes from multiple input files the tool performing the merge
    must create new, section-relative attributes where conflicts
    occur.  Similarly conflicts between section-relative attributes
    must be resolved by the creation of new symbol-relative
    attributes.  Adding support for this requirement would have again
    introduced a barrier to backwards compatiblity, and would also
    result in the attribute section being larger than an equivalent
    section using this proposal.


* The information is stored in a new section called .gnu.build.attributes.
  (The name can be changed - it is basically irrelevant anyway, it is
  the new section flag (defined below) that matters). 

  The section has the type SHT_NOTE.

  The section has a new flag set: SHF_GNU_BUILD_ATTRIBUTES
  (suggested value: 0x00100000).

  The sh_link and sh_info fields of this section should be set to 0.

  The sh_align field should be set to 4, even on 64-bit systems.
  This does mean that 8-byte values inside the notes might have to be
  relocated using unaligned relocs, and that they might have to be
  read and written using unaligned loads and stores.


* The type field of a note is used to distinguish the range of memory
  over which an attribute applies.  The name field identifies the
  attribute and gives it a value.  The description field specifies the
  starting and ending addresses for where the attribute is applied.

  Two new note types are defined:  NT_GNU_BUILD_ATTRIBUTE_OPEN (0x100)
  and NT_GNU_BUILD_ATTRIBUTE_FUNC (0x101).  These are used by the
  description field (see below).


  The description field of the note is either 0-bytes long, or else a
  pair of 4-byte wide (for 32-bit targets) or 8-byte wide (for 64-bit
  targets) addresses which indicate the starting and ending location
  for the attribute.  

  If the description field is empty, the note should be treated as if
  it applies to the same region as the nearest preceeding note of the
  same type (ie either OPEN or FUNC).

  In unrelocated files the addresses should instead be zero, with a
  relocation present to set the actual value once the file is linked.

  The numbers are stored in the same endian format as that specified
  in the EI_DATA field of the ELF header of the file containing the
  note.  The size of the numbers is dictated by the EI_CLASS field of
  the ELF header.


  The name field identifies the type and value of the attribute.
  The name starts with the string "GA", which is an abbreviation for
  GNU Attribute.  The abbreviati