For basic building instructions refer to Building 101 and incorporate the below patches after syncing or use LineageOS-UL.
The following article pertains to the optimization of legacy devices, specifically those operating on versions equal to or below 3.18.
Navigating the intricacies of legacy chipsets, especially with the introduction of obstacles such as BPF requirements by Google, can be a daunting task. However, to facilitate the booting process for A12 and beyond, a comprehensive list of essential patches has been compiled.
Graciously, these patches have been submitted to the LineageOS Gerrit for Android 12
Since not all roms track lineageos gerrit, I made a general script to adapt most roms for legacy devices: https://github.com/Meghthedev/patchscript/blob/main/patchanysource.sh
The preferred way nowadays is using the LineageOS-UL source. This ROM contains all the necessary patches to make 3.4 devices boot A12 up to A14. It has been successfully tested on a device powered by the msm8916 and msm8974 chipset. Might not fully work during qpr merges due to reworking patches, that work around googles legacy deprecations.
Commits to boot A13/A14 (qpr2) on msm8916/3.10 are here: https://github.com/acroreiser/android_device_lenovo_a6010 https://gitlab.com/TipzTeam/android-trees/android_device_cyanogen_msm8916-common
msm8974/3.4 reference to make A14 (qpr2) work can be found here https://github.com/z3DD3r/android_device_lge_hammerhead https://github.com/z3DD3r/android_frameworks_av https://github.com/z3DD3r/android_frameworks_base
3.18 trees that boot up to A14 (qpr3) https://github.com/UDPSendToFailed/android_kernel_samsung_gta2xlwifi https://github.com/Moto-experimental/android_device_motorola_msm8937-common https://github.com/droid-legacy
msm8996/3.18 references for A12/13 https://github.com/TARKZiM/device_htc_oce https://github.com/raul-16/android_device_htc_pme https://github.com/CrisBalGreece/android_device_leeco_msm8996-common