gitBOM support via environment variable GITBOM_BUILD_MODE

[yonhan3]

Signed-off-by: Yongkui Han [email protected]

[yonhan3]

This commit adds gitBOM support for binutils' 4 tools: objcopy, strip, ar, ranlib.
It also updates the readelf tool to support the new .note.gitbom ELF section.
This aligns with GCC's gitBOM support.

1. support of below environmental variables to turn on gitBOM feature:
   GITBOM_BUILD_MODE=sha1,sha256,create_adg,record_hash
   GITBOM_ADG_DIR=/any/directory

Refer to omnibor/spec#22 for details on the proposal.

2. support of the same symlink farm feature as Bomsh, to persist the artifact-id to ADG-doc mappings in the file system.
   all the symlinks are created in $GITBOM_ADG_DIR/symlinks/ directory.

3. when creating ADG doc, for single input-file case, reuse the same ADG doc of input file if the input file already has associated ADG doc.
   if input doc has no ADG doc, then create a new ADG doc, and create the symlink for the output file.
   all the ADG docs are created in $GITBOM_ADG_DIR/objects/ directory.

4. when record_hash is enabled, it records the hashes of output/inpute files in the $GITBOM_ADG_DIR/metadata/binutils/*.gitbom_raw_logfile,
   in the same format as Bomsh's /tmp/bomsh_hook_raw_logfile file, so Bomsh scripts can process these *.gitbom_raw_logfile directly.

5. binutils does not support the embed_bomid feature as in GCC/clang compilers.

6. The combinations of sha1-only, sha256-only, or sha1+sha256 are all supported.

7. "readelf -n hello" can now correctly display .note.gitbom ELF note section.

8. "unset GITBOM_BUILD_MODE" or "GITBOM_BUILD_MODE=" will turn off gitBOM support.

Here is the "readelf -n hello" output:

root@60cb7fac1537:/home/gcc-dir/gcc-gitbom/build/mytestdir# /home/binutils-gitbom-dir/binutils-gitbom/binutils-2.39/binutils/readelf -n hello

Displaying notes found in: .note.ABI-tag
  Owner                Data size        Description
  GNU                  0x00000010       NT_GNU_ABI_TAG (ABI version tag)
    OS: Linux, ABI: 3.2.0

Displaying notes found in: .note.gitbom
  Owner                Data size        Description
  GITBOM               0x00000014       NT_GITBOM (SHA1 GITOID)
    SHA1 GitOID: 616620ebaeb580c14e0138456a961ebed2df41a2
  GITBOM               0x00000020       NT_GITBOM (SHA256 GITOID)
    SHA256 GitOID: c76284ff3b421d38a69c6e050ff6bcda2700af0713b0f2c5103d94464baa6152
root@60cb7fac1537:/home/gcc-dir/gcc-gitbom/build/mytestdir#