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Sm-j700m cpu is arm64 but only allows 32bits android on it.

From here: https://www.reddit.com/r/LineageOS/comments/p9p3s3/comment/h9zan52/

I thought that, if the bootloader could be replaced or tweaked (change some bytes on it), it could allow 64bits android (lineage os 64bits build) to be installed on it.

But these are the only clues i got til now, any tips? Can it be done? Is there some software for that device, or other devices, that could do that on that device?

Related? Unlocking bootloader to change rom or firmware

VeganEye
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  • https://forum.xda-developers.com/showthread.php?t=4057503 – alecxs Aug 23 '21 at 07:03
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    If your bootloader boots the kernel only in 32 bit mode, the only way: contact your OEM, get the bootloader source code and their private key, make necessary changes to the source code, recompile it to boot in 64 bit mode, sign it with their private key and flash to the device. Now compiling a 64-bit ROM (kernel and AOSP code) is up to you: Could a 64-bit hardware device run a 32-bit Android version? – Irfan Latif Aug 23 '21 at 07:04
  • Running a 64bit Linux on that phone with 1.5GB RAM doesn't make sense at all as there is no advantage. Also 64bit software usually requires slightly a bit more RAM and RAM is already short on your phone. And if you have an app that requires 64bit than it will also demand more RAM, more as your device can provide. – Robert Aug 23 '21 at 09:51
  • @IrfanLatif can root+adb be used to make the bootloader's private key unnecessary? I just think samsung will give nothing, but i may be wrong. – VeganEye Aug 23 '21 at 18:15
  • No. Root / ADB are high level userspace things. Under userspace lies kernel, and under kernel lies bootloader. So they have nothing to do with each other. Root just gives you access to the bootloader. You can extract it but cannot modify it. Bootloader binaries are signed with OEM's private key. Read about Android Verified Boot to know more. Any changes to bootloader are near to impossible. Except if the bootloader is open-source e.g. LittleKernel used in some Mediatek devices. But OEM's signature can be a limiting factor there too. Private keys are meant to be “private”, they aren't shared. – Irfan Latif Aug 24 '21 at 05:17
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    https://duckduckgo.com/?q=How+to+modify+Android+bootloader. Understanding OEMs' chain of trust: https://lineageos.org/engineering/Qualcomm-Firmware/. Android boot process: https://android.stackexchange.com/a/220678/218526 and https://javigon.com/2012/08/24/from-poweron-to-android-the-boot-sequence/ – Irfan Latif Aug 24 '21 at 05:48

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