Fix SMS reception on Samsung Galaxy S20 FE 5G

Recent Samsung vendor firmware, like in G781BXXSAHXC6 from April 2024, breaks SMS reception with recent GSI firmware, for example Andy Yan's LineageOS 20 GSI from https://sourceforge.net/projects/andyyan-gsi/files/lineage-20-light/

Based on the same fix for a different device (https://github.com/IverCoder/a03nnxx-ril-rollback), the 2 files libsec-ril.so and libsecril-client.so have to be extracted from an older Samsung firmware before June 2023, e.g. G781BXXS5HWD4

Here are the steps it took me to fix SMS reception:

• Download AP_G781BXXS5HWD4_G781BXXS5HWD4_MQB64445591_REV00_user_low_ship_MULTI_CERT_meta_OS13.tar.md5.zip from https://samfw.com/firmware/SM-G781B/DBT/G781BXXS5HWD4

• Unzip downloaded file

  $ unzip AP_G781BXXS5HWD4_G781BXXS5HWD4_MQB64445591_REV00_user_low_ship_MULTI_CERT_meta_OS13.tar.md5.zip

• Install android-sdk-libsparse-utils and lz4

  $ sudo apt install android-sdk-libsparse-utils lz4

• Extract sparse image of super partition

  $ mkdir AP_G781BXXS5HWD4
  $ cd AP_G781BXXS5HWD4
  $ tar -xvf ../AP_G781BXXS5HWD4_G781BXXS5HWD4_MQB64445591_REV00_user_low_ship_MULTI_CERT_meta_OS13.tar.md5 super.img.lz4
  $ unlz4 super.img.lz4

• Convert sparse super image to raw super image

  $ simg2img super.img super.img_raw

• Build lpunpack from source

  $ cd ..
  $ git clone https://github.com/LonelyFool/lpunpack_and_lpmake.git 
  $ cd lpunpack_and_lpmake
  $ ./make.sh

• Extract vendor image from raw super image

  $ cd AP_G781BXXS5HWD4
  $ mkdir super.img_raw_extracted
  $ ../lpunpack_and_lpmake/bin/lpunpack -p vendor super.img_raw super.img_raw_extracted/

• Now we have an Ext4 image

  $ file super.img_raw_extracted/vendor.img 
  super.img_raw_extracted/vendor.img: Linux rev 1.0 ext2 filesystem data, UUID=70b6de35-be95-5001-bd80-c63c433cd480, volume name "vendor" (extents) (large files) (huge files)

• Mount vendor image to access files

  $ mkdir vendor_mounted
  $ sudo mount -o loop super.img_raw_extracted/vendor.img vendor_mounted
  $ mkdir ril_patch
  $ cp vendor_mounted/lib64/libsec-ril.so ril_patch/
  $ cp vendor_mounted/lib64/libsecril-client.so ril_patch/

• Make sure you have MTP, USB debugging and ADB root enabled

• Connect device via USB and copy ril_patch directory to common storage (mounted as /sdcard)

• Open ADB shell, become root, make /vendor writeable, replace existing files and reboot

  $ adb shell
  tdgsi_arm64_ab:/ $ su
  :/data/data # mount -o remount,rw /vendor
  :/data/data # cp /sdcard/ril_patch/libsec* /vendor/lib64/
  :/data/data # mount -o remount,ro /vendor
  :/data/data # reboot

• After reboot, enter simcard PIN, unlock screen and send SMS from another phone. You should be able to receive SMS now.