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[GUIDE][BOOTLOADER,TWRP, ROOT]Lenovo TAB3 8/TB3-850F

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limited_imagination

Senior Member
Nov 2, 2013
66
39
Greetings. Okay I seem to have broken my first rule of thumb when staring on this project: NEVER ASSUME ANYTHING. So I assumed that the LOS 14.1 ROM was integrated with a LOS boot image. Had I read the threads a little more thoroughly, I could have saved myself a ton of trouble. As you guys probably already knew, this is a dirty port hybrid boot image, with a LOS ramdisk and a stock Lenovo kernel. My trouble with SELinux enforcing, merged changes and force closing crashes have now come to light. (I do have to assume that either (1) Lenovo never released the kernel source code for the Tab3 8, or (2) nobody has sat down and actually compiled a kernel from source.) I had to go back to the drawing board on a large sum of my work. I just wanted to give an update and apologize for my huge oversight. Now that I have a full perspective of everything, I feel confident that things will go a little smoother. Plus, this will give me a base template for porting other custom builds. Our present kernel, 3.18.19, supports Android 6.0 all the way up to Android 10.
Anyway I'm elbows deep once again. Wish me luck....
Hi again Viva. Just checking back on this thread to see how you are doing.

I expect you already found a copy of the source code for this device that Lenovo posts here: https://pcsupport.lenovo.com/cr/en/products/tablets/a-series/tab3-8/downloads/ds112711

You may have noticed that much earlier in this thread, I was trying to get that code to build a kernel alone, not as part of an LOS rom. I was never successful, despite much mangling of the official source code in an attempt to remove or alter code that caused errors that borked the build process. IIRC, somewhere back in the mists of this thread, I actually mangled it enough to complete a kernel build, but flashing that kernel to the device soft bricked it.

Subsequently I have learned a bunch more about the build process, and was able to successfully build LOS for my Mi Pad 4: https://forum.xda-developers.com/t/...ad4-mipad4-plus.3989187/page-52#post-85504115

In all the trial & error for the Mi Pad 4 LOS, I discovered that a lot of build errors were created by incorrect configurations of my Linux VM, and the final piece of the puzzle was to install and enable ZRAM. When I ran the build after that, it got to the end, although still throwing a few error messages and warnings along the way.

All this to say, maybe if I had configured my Linux VM better when I was playing with the kernel source code for the TB3-850F, then maybe it would have built correctly while still throwing a few error messages along the way.

If there is anything I can do to help, shoot me a PM, and I'll see what I can do. I still am pretty inexperienced, but having got a successful LOS 17.1 build to compile and then flashing it successfully to my Mi Pad 4, I am at least a "build bot" status now. :)
 
Hi again Viva. Just checking back on this thread to see how you are doing.

I expect you already found a copy of the source code for this device that Lenovo posts here: https://pcsupport.lenovo.com/cr/en/products/tablets/a-series/tab3-8/downloads/ds112711

You may have noticed that much earlier in this thread, I was trying to get that code to build a kernel alone, not as part of an LOS rom. I was never successful, despite much mangling of the official source code in an attempt to remove or alter code that caused errors that borked the build process. IIRC, somewhere back in the mists of this thread, I actually mangled it enough to complete a kernel build, but flashing that kernel to the device soft bricked it.

Subsequently I have learned a bunch more about the build process, and was able to successfully build LOS for my Mi Pad 4: https://forum.xda-developers.com/t/...ad4-mipad4-plus.3989187/page-52#post-85504115

In all the trial & error for the Mi Pad 4 LOS, I discovered that a lot of build errors were created by incorrect configurations of my Linux VM, and the final piece of the puzzle was to install and enable ZRAM. When I ran the build after that, it got to the end, although still throwing a few error messages and warnings along the way.

All this to say, maybe if I had configured my Linux VM better when I was playing with the kernel source code for the TB3-850F, then maybe it would have built correctly while still throwing a few error messages along the way.

If there is anything I can do to help, shoot me a PM, and I'll see what I can do. I still am pretty inexperienced, but having got a successful LOS 17.1 build to compile and then flashing it successfully to my Mi Pad 4, I am at least a "build bot" status now. :)
Great to hear from you. And congratulations on your Mi Pad 4 build of LOS 17.1. So it sounds as though you compiled the entire ROM from source. Impressive. Yeah the source code released by Lenovo for the TB3-850F seems to include a proprietary OS bundle in addition to kernel source. Doesn't look like the typical kernel source code archive, but maybe I'm looking at itt wrong. My difficulties on smoothing this ROM out mainly involve the fact that this build was dirty ported twice before I began work on it. I encountered a lot of unforeseen obstacles. I fixed some bugs, included some vendor overlays for dark mode, updated libs and databases, etc., only to have the entire ROM crash when I put things back together. On a positive note, I have assembled pretty well the entire framework needed to port additional custom ROMs in the future. But yes, I will surely PM you and pique your brain on a couple of topics very soon.I haven't had much free time lately either, so that's been a bummer on this project. Anyway thank you sincerely for your offer of assistance and your encouragement. I shall be in touch.
 
When do we receive our refunds? :)
😂😍
Hey I'm getting slower in my old age. Last time I rushed on a ROM I fell and broke a hip. Haven't been right since . Ok the hip part I made up but old age is creeping up. All jokes aside I'm making good headway. I ended up taking the original port ROM and laying it out fresh on the drawing board. I was running into unforeseen issues due to the ports and mods that were done previously. A port ROM is much akin to a hobby go-kart you might find at a flea market or yard sale. It's a collective montage of tweaks, mods and alterations performed by everybody who has owned it. Shortcuts are made and corners are cut. It's called a dirty port for a reason. 😉
Im still at it. @limited_imagination has graciously offered his hand in assistance on this project. He is an official code compiler now so his offer will benefit the cause no doubt. He recently compiled LOS 17.1 for the Mi Pad 4 from source code. Anyway friend good to hear from you as always. Oh, the refunds have been sent out. You know the old saying...the check is in the mail. 😛 Hold your breath and keep watching that mailbox.
 
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Gents I am finally back and proud to say I do have something fresh and new for our beloved Tab3. I have ironed out an up-to-date TWRP custom recovery, bringing the code base up to 3.2.1-0 with full theme support. I'm posting it now and will post a link here as well once my thread is done.
So without further ado, an updated TWRP build with a fresh new look. I have more treats to come for the Tab3 8.
 
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  • 12
    This guide, for the Lenovo Tab 3 8" (TB3-850F), has 3 purposes:

    1. Unlocking your bootloader;
    2. Installing TWRP custom recovery;
    3. Attaining superuser privileges (root) of the stock OS.

    NOTE:
    I can attest & confirm that this method has worked 100% on at least 7 devices of my own. Please read and re-read the instructions carefully before proceeding. If you follow this tutorial exactly as delineated, you should have no adverse issues in unlocking your bootloader, flashing custom recovery, or achieving systemless root of the stock Android OS.




    MENTIONS & THANKS:
    Based on XDA Senior Member @Hemphiz's groundbreaking root and custom recovery for this device, I am now revising this thread wth improved step-by-step instructions based on members' feedback and experiences. Thanks @Hemphiz for your research, assimilation of necessary files, and for breaking ground on this tablet. Thanks also for your granting me ownership of the thread. Your contributions are greatly appreciated by many. Thanks to the great @Chainfire for his flashable systemless rooting script. Thanks to @jemmini for compiling TWRP for this tablet. Finally, thanks to the many members who have tested this guide and provided much needed input & user experience.

    DISCLAIMER: As always, please be reminded of the risk involved with flashing a custom recovery and/or attempting to attain superuser privileges of your Android OS. I will not be held responsible for devices bricked or otherwise rendered inoperable as a result of this thread. You assume full responsibility for any good or bad which may result from proceeding any further. However, with that having been said, I will provide any and all support possible. Read and follow the foregoing steps thoroughly and carefully prior to proceeding. NOTE: THIS GUIDE IS INTENDED ONLY FOR THE LENOVO TAB 3 8"/TB3-850F.

    REQUIREMENTS:

    1. Minimal ADB & Fastboot v1.4 (or newer) Windows Installer;
    2. Windows PC or laptop (Mac may be used; however this guide is intended for Windows 7 and newer operating systems);
    3. Official Lenovo USB Device Driver v1.1.21;
    4. TWRP v3.0.1 for the TB3-850F;
    5. ADB Driver Installer for Windows;
    6. SuperSU v2.82-SR5 flashable zip.

    (All files, drivers & utilities for this process are available in the below download link)

    DOWNLOAD LINK: https://drive.google.com/folderview?id=1l-YN5aXmjDF3O1bHxFHVIxLKuvd847Q9




    INSTRUCTIONS:


    1. First and foremost, unlocking the bootloader is necessary. Also, this step is a good place to make some requisite preparations. Power on your Tab 3 and select SETTINGS once booted up. Go to ABOUT DEVICE, find BUILD NUMBER, and tap it 7 or 8 times until DEVELOPER OPTIONS is enabled. In DEVELOPER OPTIONS, tick OEM UNLOCKING and USB DEBUGGING. On your PC, install the Minimal ADB & Fastboot utilities, the ADB Driver Installer, and the Lenovo USB Driver Installer. Connect your Tab 3 to your PC with the supplied (or quality equivalent) OEM charging/syncing cable. Open a command window in your ADB/Fastboot directory, by holding SHIFT and right clicking in the desired path. In the command window, type: adb devices & press RETURN. If your device is connected properly, the command window will display a string of numbers/letters, which represent your device's serial number. If your serial number does not appear in the window, try changing USB ports, change syncing cables, or try reinstalling the ADB Drivers. Once properly connected, type adb reboot bootloader & press RETURN. Your tablet should boot into Fastboot Mode, which will be displayed in white bold letters on your device's display once complete. Once in Fastboot Mode, type fastboot oem unlock & press RETURN. Your device will prompt you to press Volume Up to proceed with unlocking the bootloader, or Volume Down to cancel the process. WARNING: UNLOCKING THE BOOTLOADER AUTOMATICALLY INITIATES A FACTORY DATA RESET. YOU WILL LOSE ANY UNSAVED VIDEOS, MUSIC, PERSONAL FILES, ETC.

    2. Now that your bootloader is unlocked, you are ready to flash TWRP. Download the twrp.img file from my link and save it to your PC in the ADB/Fastboot path/directory. Also, save a copy of the file on your device's internal storage or external micro SD card. Since your device underwent a factory data reset, you will again need to enable DEVELOPER OPTIONS & tick OEM UNLOCKING & USB DEBUGGING as you did in Step 1. When you have done this, again open a command window, ensure a proper connecion, & type adb reboot bootloader & press RETURN. Once in Fastboot Mode, type fastboot boot twrp.img & RETURN. EXTREMELY IMPORTANT NOTE: this device's boot image is secured with dm-verity. Leave the /system partition as read-only when prompted by TWRP. Mounting /system as read/write at this point will result in a boot loop. Flashing SuperSU, as outlined in Step 3, will patch dm-verity and fix this.
    From the TWRP main menu, select INSTALL, select the image file option in the bottom right of the screen, navigate to the location where you saved twrp.img in device storage or external storage, and commence the installation. Be certain and correctly choose "recovery" when prompted by TWRP. Now select REBOOT, then RECOVERY. Your TWRP custom recovery should now be successfully installed on your device's /recovery partition.

    3. Now, it is time to root this tablet. Download & save a copy of the SuperSU v2.82-SR5 zip file to the tablet's internal or external storage. In TWRP main menu, select INSTALL & navigate to the saved SuperSU zip. Commence with installation. Systemless root mode will unpack, modify, repack and flash the patched boot image. Once done, reboot system. Your Android OS should now have full systemless root, and the /system partition may now safely mount as read/write.

    TROUBLESHOOTING:

    In the event your device becomes stuck in a bootloop, or is otherwise failing to boot into the OS, the following is a link to my stock firmware images thread for this device. NOTE: the following link will be beneficial only if your device successfully boots into Recovery/Fastboot mode. This link provides stock partition images of /boot, /recovery, /logo & /system. Typically, flashing the stock boot & system images will get you up & running again, and will restore the Android OS to stock condition.
    https://forum.xda-developers.com/an...o-tab-3-8-tb3-850f-android-6-0-t3593043/page5

    In the unfortunate event that you encounter a brick (your device fails to boot into the OS or Recovery Mode), please visit @r&xp's thread on unbricking your device & restoring it to factory stock condition. Members using his thread be sure to thank @r&xp. His collection of necessary files & comprehensive instructions has saved many, many bricked tablets. https://forum.xda-developers.com/android/help/lenovo-tab-3-8-tb3-850f-unbrick-root-t3598727
    5
    News Flash for users of TB3-850F!

    We now have stable LOS14.1 for TB3-850F! :)

    See post above. Regards, PW.

    Alerting:
    @Hemphiz
    @Lister Of Smeg
    @mtpc
    @stonedpsycho
    @fran89
    @r&xp
    @john3voltas
    @Garcy23
    @voland34
    @DeblaGaming
    @sorun343
    @limited_imagination
    4
    Yeah, I'm not sure how I screwed it up but I'm glad it's working. In order to get into adb I tried the method you mentioned of holding the volume+ for 5 seconds and then plugging in the usb cable. From there I used adb to reboot into the bootloader. I tried flashing the boot and recovery images from there, but it didn't seem like they took. So then I used the fastboot boot command with the TWRP image, but it wouldn't let me access the data partition for some reason. I went to reboot and then all hell broke loose and it was just rebooting through TWRP failing with openscript and then rebooting again nonstop. I couldn't manage to shut it off completely even holding the power button for 30 seconds or so. I figured I was screwed, but held the volume up, volume down (and I think power?) at the same time and suddenly it actually launched TWRP. However, it couldn't access the data partition for some reason. I threw the stock boot, recovery, and system images on an SD card and then flashed them all and that finally got it working.

    I've rooted other phones, but I've had hardly any experience with adb. Fortunately I feel like I did learn quite a bit from screwing up, which is always a plus.
    Great work. Sounds like a good learning experience for you also. These devices on a MediaTek platform are a horse of a different color indeed. I've bricked a good handful of these devices through trial & error myself. By the way, please be sure and hit the thanks button on the OP. @Hemphiz done an excellent job initiating TWRP & root for this great budget tablet.
    I am currently working on a stock based 6.0.1 ROM for this device: rooted, deodexed, debloated & zip aligned. I'll add a few baked-in features like Substratum & Viper4Android. Also I'll add a couple of tunable governors & tweaks to the stock kernel. I'm terribly tied up at work, resulting in having to take a couple weeks break from Android, but I should be up & running again in 3 weeks or so.
    Anyway, I'm very glad it worked out for you. Try this to iron out any bugs with booting TWRP. First, save a copy of the twrp.img to your internal storage or external micro SD card. Next, get your device into TWRP. Select INSTALL, then select the flash img option in the bottom right-hand corner. Navigate to the location of your TWRP.img, commence to install and select "RECOVERY" when prompted to do do. Once done, wipe Cache & Dalvik/ART. Reboot system. This should allow smooth booting of TWRP, with no loops or lags.
    4
    my tablet is tab 3-850f_S100030_161209_row

    so i guess it could be possible to root...i am little be afriad to do that...

    this step 6

    #6 Now you need to boot to your custom recovery via the button combo for the device. (imo this tablet is a pain to boot into recovery compared to most devices) power off the phone. Wait a few seconds. Now hold the power button - then while still holding the power button press Volume up and then Volume down. Hold it for about a second then let them all go. If it worked then you will get the usual boot logo followed by the main twrp screen. Swipe to allow it to make modifications. If it boots into the Chinese recovery thing then just turn it off and try again. I would suggest getting an app that allows you to "reboot to recovery" once your all done and rooted. For root. Simply put the "Supersu sr3" zip in the storage of your tablet. Then flash it via twrp. "install - find where you put the zip - flash - reboot system" Done.

    would someone be more specific to explain...i get my tab in boot mode with holding power buton and volume down an up......and in display is simbol of android with mesage no command..its confused me...

    ---------- Post added at 01:45 PM ---------- Previous post was at 01:28 PM ----------

    i found a solution...press power button 2 seconds and quick press once volume up....

    now i am in recovery boot menu...

    so if someone to explain more specific this step 6

    thanx for advices

    regard

    See this post from Lister of Smeg's TB3-850F Thread, re root & recovery for TB3-850F. Note 'To Enter TWRP':

    filedropper.com/tb3850froot (for files)
    Quote:
    Originally Posted by mtpc
    Hey guys, It's me again. I managed to crack down the russian CAPTCHA and downloaded those files, and it just WORKS! I now have full root on my TB3-850f. I wrote down simple HOW-TO:
    [Slightly ammended by Peter Wallace (Original Post #49)]
    1) Copy SuperSU-v2.79-SR1-20161221223537.zip to the tablet
    2) Enable developer and USB debugging
    3) Open cmd (command Window) in folder with ADB and FASTBOOT
    4) Type these commands:adb reboot bootloader
    Then:fastboot oem unlock
    5) Hold down power button and reboot. Repeat 2) and enable OEM UNLOCK
    6) Repeat 3) and type:adb reboot bootloader
    7) then type:fastboot boot recovery.img (must be copied in the same folder as adb.exe and fastboot.exe)
    (Don't flash recovery yet - system will replace stock recovery before you have root)
    8) Use TWRP to install SuperSU. - Now you have ROOT (Systemless) (can update to SR3, etc)
    9) Repeat 3) and type: adb reboot bootloader
    10) Type:fastboot flash recovery recovery.img - Now your new TWRP recovery will be permanent.
    11) Use TWRP to reinstall SuperSU as lost in step 10 - Now you have ROOT (Systemless).

    To Enter TWRP:
    After powering down, press power, wait 1 sec then hold both vol up & down also (all 3 buttons) until vibrates.

    I also uploaded the files here: filedropper.com/tb3850froot

    Peter W:
    Here is link to latest 850f rom:
    http://lenovo-forums.ru/files/file/1549-lenovo-tab3-a8-tb3-850f_s100030_161209_row/
    Which takes you to https://cloud.mail.ru/public/8T5R/RWCkuBz19
    4
    Thanks for the guide!
    Everything works but when I reboot into recovery I just get the dead android with no command under him..
    I tried two times with same result Fastboot reports twrp flashes ok

    Any ideas?

    Thanks
    Not to hijack the OP's thread but here are my thoughts. The dead Android indicates that TWRP did not successfully flash to your /recovery partition. Sounds like stock recovery is still installed. First, place a copy of twrp.img on your device's internal storage or on an external micro SD. Try this: instead of typing the command "fastboot flash recovery twrp.img", type " fastboot boot twrp.img" (assuming your twrp file is named twrp.img. If it isn't, rename it twrp.img for simplicity purposes). This command will temporarily boot your device into TWRP recovery. From the main menu on TWRP, select INSTALL. In the bottom right of the screen, select the option for "img" files. Navigate to where you stored "twrp.img" and select it. Install it to "RECOVERY" when prompted. Once it flashes, select REBOOT then select RECOVERY. Your device should now successfully boot into TWRP recovery.