How it works:
1. build/make/core/Makefile generates a txt file with the kernel
version, which is taken from an explicit BOARD_KERNEL_VERSION value,
or extracted from the kernel image on the source tree, or extracted
from the kernel image extracted from the prebuilt boot.img.
The file is saved at
$ANDROID_PRODUCT_OUT/obj/PACKAGING/check_vintf_all_intermediates/kernel_version.txt.
2. If PRODUCT_ENABLE_UFFD_GC is "default", meaning the GC type needs to
be determined by the kernel version, build/make/core/Makefile copies
kernel_version.txt to
out/soong/dexpreopt/kernel_version_for_uffd_gc.txt.
3. build/soong/dexpreopt/config.go writes the the UFFD GC flag to
out/soong/dexpreopt/uffd_gc_flag.txt. The flag is determined by an
explicit PRODUCT_ENABLE_UFFD_GC value or by contruct_uffd_gc_flag.py,
which reads kernel_version_for_uffd_gc.txt and determines the flag
accordingly.
4. dex2oat takes the UFFD GC flag from uffd_gc_flag.txt.
5. post_process_props.py mangles ro.dalvik.vm.enable_uffd_gc based on
the same logic.
Bug: 321751629
Bug: 319554951
Bug: 318763448
Bug: 319648491
Test: m --no-skip-soong-tests nothing
Test: atest uffd_gc_utils_test
Test: Build with `OVERRIDE_ENABLE_UFFD_GC=default m` for device with no
UFFD support -
1. Check the existence of `-Xgc:CMC` in
out/soong/dexpreopt_arm64/dex_bootjars/android/system/framework/arm64/boot.invocation
(dex2oat invocation for a boot image)
2. Check the existence of `-Xgc:CMC` in
out/soong/.intermediates/packages/apps/Settings/Settings/android_common/dexpreopt/Settings/oat/arm64/package.invocation
(dex2oat invocation for an app defined in .bp)
3. Check the existence of `-Xgc:CMC` in
$ANDROID_PRODUCT_OUT/obj/APPS/Dialer_intermediates/oat/arm64/package.invocation
(dex2oat invocation for an app defined in .mk)
4. Check the value of ro.dalvik.vm.enable_uffd_gc in
$ANDROID_PRODUCT_OUT/product/etc/build.prop
Test: Build with `OVERRIDE_ENABLE_UFFD_GC=default m` for device with
UFFD support, and do the steps above.
Test: Build with `OVERRIDE_ENABLE_UFFD_GC=true m`, and do the steps
above.
Test: Build with `OVERRIDE_ENABLE_UFFD_GC=false m`, and do the steps
above.
Change-Id: I035ad32233e49e2a30ce11f6c7c318a648511ef8
