[Replicant] backup stock ROM without root

[Denis 'GNUtoo' Carikli]

On Mon, 03 Sep 2018 19:32:00 +0000
kurtis <kurtis at riseup.net> wrote:

> Fil,
> 
> I had a random idea last night after thinking more about what you are
> trying to accomplish.

> 
> https://blog.forkwhiletrue.me/posts/u-boot-on-galaxy-s3/
> 
> The resistor is shown here:
> https://blog.forkwhiletrue.me/images/i9300_resistor.jpg
Many SOCs have 'boot pins', theses are pins that will tell the SOC on
which external storage devices (or protocols) it should try to boot and
in which order to try them. So to change that you need to set theses
pins to ground or VCC, for instance by changing or moving resistors.

On some single board computers it's really easy to do that because one
of theses pins is connected to a button. On some smartphones it's hard
to do as you would need to move some resistors.

The method you describe should work. If u-boot gets USB support, you
will then be able to run something like that: 'ums 0 mmc 0' which would
export the eMMC on the USB. You can then use your favorite disk copying
program (like ddrescue or gnome-disks).

The issue is that this approach works fine for people used to modify
and/or repair electronics, but it's way less trivial for people lacking
such skills.

It is also far from being universal, as the resistors location are
device specific.

Denis.
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