tree f97b4179366a813754550846de8e91eb2f39fa2a
parent bff959a5ab1eaeb7bf42782d06333f276306504c
author Vladimir Oltean <olteanv@gmail.com> 1547687254 +0200
committer Michael Bestas <mkbestas@lineageos.org> 1551624293 +0200

extract_utils: introduce support for executing blob fixups

* Traditionally, the task of hex-editing blobs has been approached in 2 ways:
  (1) Do it out-of-band, commit the modified blob, and record its edited
      sha1sum in proprietary-files.txt (aka pin it).
  (2) Do it in-band, by adding code to the device-level extract-files.sh
      (usually this performs patchelf or sed). This code runs after the
      extract_utils functions were invoked.
* Problems of approach (1):
    - It relies on verbal (basically commit message) documentation of
      the hex-editing that was done. Makes it more difficult to reproduce.
    - Each time blobs are updated, pinning needs to be temporarily removed,
      hex-editing done again manually and new hash put back.
* Problems of approach (2):
    - It is incompatible with the concept of pinning, which is useful
      for kanging blobs from another device. A pinned blob would either:
        - Match the hash, get hex-edited, then it won't match the hash
          next time around.
        - Not match the hash (because of, say, hex-editing), then the
          extraction script would use an unwanted blob version instead of the
          pinned one (either that, or say "!! file not found in source").

* In summary, this patch adds system-wide support for approach (2) in order
  to address the aforementioned shortcomings.

* At device level, users of extract_utils who wish to perform blob
  fixups can override a blob_fixup() Bash function in their
  extract-files.sh immediately after running "source ${HELPER}". The
  blob_fixup() function will be called by the common extract() function
  after extracting every individual blob, giving the user the
  opportunity to hook custom code after this operation takes place.

* In proprietary-files.txt, the line corresponding to this blob which
  needs fixups can look in one of 2 ways:

(a) vendor/lib64/vendor.qti.gnss@1.0_vendor.so

    Do this if you are taking the blob from the stock ROM. The fixup
    script will always run after the blob is extracted.

(b) vendor/lib64/vendor.qti.gnss@1.0_vendor.so|249c76153f8de014bf2dd2ab623ee3d87741fbc8|f7e9ee8e3804887a2f3939128e860767e6f27258

    Do this if you are kanging the blob from somebody else. The pinning
    logic now applies for both the pre- and the post-fixup hashes. The
    fixup script will only run if the blob doesn't match the hex-edited blob,
    although the fixup script should really be idempotent.

Change-Id: Ifdd73c885d995c645f6210597537693d1a2f903f
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>