Yes, you have to “treblize” your A3 2017. I think i’ve used this repartitioner script : [TOOL][A320FL/F/Y] Repartition script for vendor support | XDA Forums
This will make a system partition and a vendor partiton, both separated from each other. The GSI image is the system image for the system partition, so you have to have a vendor partition from a rom. For example, i’m using the crDroid v6.17 vendor partition (now it’s 6.21) : [ROM][10][ARM64][A320] crDroid v6.21 for Galaxy A3 2017 [10.08.2021] | XDA Forums
In this crDroid thread, the link to the OrangeFox is wrong, but there is a new Repartitioner Script (2021) link. I haven’t used it.
Just after flashing a custom recovery (TWRP or OrangeFox) you have to do a backup of your EFS partition (save it on your SD card, not on the internal memory of the phone, and make a copy on your computer to be safe).
With TWRP you will maybe have some data partition errors and will have to wipe data partition every time you will go into recovery mode. So i’m using OrangeFox (flashed after TWRP). But I believe you can’t flash an .img on a specific partition with OrangeFox, maybe I’m wrong. And i never have managed to sideload with my A3 2017 on my computer.
The image you will need to flash on your A3, when you will have treblized it, is an Arm64 A/B image.
I make some changes in the original GSI image (i uncompress the .xz file to extract the .img system file, rename it in “system.img” and I use SuperR’s Kitchen to extract all the files of the system.img). I do my mods on the extracted files and then i repack it (still with SuperR’s Kitchen) in the traditional format of most of custom roms (like crDroid), so the original system.img becomes 3 files : system.new.dat.br + system.patch.dat + system.transfer.list
like in the crDroid zip rom. Then i put these 3 files in the crDroid zip to replace the 3 original files of this rom and I flash this modified zip with OrangeFox. [In fact, I’ve modified the script of the zip to just flash the system partition files, not the vendor files, since I already have the vendor partition and I don’t update it, it’s quicker.] But I’m a “newbie”, so I’m not really a good professor for you, and the whole process is not fresh in my head.
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