Quote:
Originally Posted by vgreader
Hi
May I ask about difference between JB and Hack. Why does one survives Amazon update and the other doesn't.
If there is a thread that explains these concepts please let me know.
Thanks
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I don't know what your background in computer systems is, so the following might be just noise to you.
For the touchscreen based devices:
The Kindles are 'dual boot' devices (two operating systems available) named by their purpose: 'main' and 'diags'.
The flash storage is divided into four partitions (each a file system backing store).
The partitions (and its associated file system) are used for the following:
- 'main' operating system
- 'diags' operating system
- persistent (user) run-time storage (can not be seen by the user)
- persistent (user) storage (can be seen by user over USB cable)
Update_*.bin packages are signed, both Amazon's and ours.
What is called a 'jail break' here is simply our signature certificate, which is added to the Kindle's key storage (part of #1) which also holds Amazon's signature certificates.
Since (about) firmware version 5.2, Amazon updates have been a complete image replacement of the contents of the first (#1) partition.
Which means an Amazon image update over-writes the signature certificates. (the actual 'JB' file)
The 'diags' system could be, but never has been, updated OTA.
The other two partitions, containing information both implicitly and explicitly added by the user are not part of the update.
Both for technical and legal reasons (mostly, the contents are not the property of Amazon).
The Kindle's operating system (Linux) executes specific files in a specific order during its IPL (it boot sequence in more modern terms).
Some of those exist in partition #3 (in portions untouched by update process).
When the files that we add to that IPL sequence execute, part of what they do is re-install our signature certificate in the (now) new Amazon image.
That is the 'bridge' code that bridges the certificate across 'main' system image replacement.
None of what we do here, or accept here, is closed source.
Everything is open source, publicly available for inspection and review.
If you need any more of the gory details, "Let the source be with you".
I.E: RTFS