Determine whether to enable userfaultfd GC at build time.

This is determined by:
- a product config flag
- the vendor API level

It is then passed to the device as a system property
"ro.dalvik.vm.enable_uffd_gc".

This change is a no-op change. It doesn't enable userfaultfd GC by
default. OVERRIDE_ENABLE_UFFD_GC=default can be passed to the build
system to enable userfaultfd GC for testing purposes.

Bug: 242553398
Test: -
  1. lunch aosp_redfin-userdebug
  2. OVERRIDE_ENABLE_UFFD_GC=default build/soong/soong_ui.bash --dumpvars-mode --vars=ENABLE_UFFD_GC
  3. See "false" in the output
Test: -
  1. lunch aosp_oriole-userdebug
  2. OVERRIDE_ENABLE_UFFD_GC=default build/soong/soong_ui.bash --dumpvars-mode --vars=ENABLE_UFFD_GC
  3. See "true" in the output
Test: -
  1. lunch aosp_redfin-userdebug
  2. OVERRIDE_ENABLE_UFFD_GC=true build/soong/soong_ui.bash --dumpvars-mode --vars=ENABLE_UFFD_GC
  3. See "true" in the output
Test: -
  1. lunch aosp_oriole-userdebug
  2. OVERRIDE_ENABLE_UFFD_GC=false build/soong/soong_ui.bash --dumpvars-mode --vars=ENABLE_UFFD_GC
  3. See "false" in the output
Change-Id: Ifd6e6cddb502315912ff949619a5b526ae0d73ff

core/OWNERS

@@ -1,4 +1,5 @@
-per-file *dex_preopt*.* = ngeoffray@google.com,skvadrik@google.com
+per-file *dex_preopt*.* = jiakaiz@google.com,ngeoffray@google.com,skvadrik@google.com
+per-file art_*.* = jiakaiz@google.com,ngeoffray@google.com,skvadrik@google.com
 per-file verify_uses_libraries.sh = ngeoffray@google.com,skvadrik@google.com
 
 # For global Proguard rules

core/art_config.mk

@@ -0,0 +1,46 @@
+# ART configuration that has to be determined after product config is resolved.
+#
+# Inputs:
+# PRODUCT_ENABLE_UFFD_GC: See comments in build/make/core/product.mk.
+# OVERRIDE_ENABLE_UFFD_GC: Overrides PRODUCT_ENABLE_UFFD_GC. Can be passed from the commandline for
+# debugging purposes.
+# BOARD_API_LEVEL: See comments in build/make/core/main.mk.
+# BOARD_SHIPPING_API_LEVEL: See comments in build/make/core/main.mk.
+# PRODUCT_SHIPPING_API_LEVEL: See comments in build/make/core/product.mk.
+#
+# Outputs:
+# ENABLE_UFFD_GC: Whether to use userfaultfd GC.
+
+config_enable_uffd_gc := \
+  $(firstword $(OVERRIDE_ENABLE_UFFD_GC) $(PRODUCT_ENABLE_UFFD_GC))
+
+ifeq (,$(filter-out default,$(config_enable_uffd_gc)))
+  ENABLE_UFFD_GC := true
+
+  # Disable userfaultfd GC if the device doesn't support it (i.e., if
+  # `min(ro.board.api_level ?? ro.board.first_api_level ?? MAX_VALUE,
+  #      ro.product.first_api_level ?? ro.build.version.sdk ?? MAX_VALUE) < 31`)
+  # This logic aligns with how `ro.vendor.api_level` is calculated in
+  # `system/core/init/property_service.cpp`.
+  # We omit the check on `ro.build.version.sdk` here because we are on the latest build system.
+  board_api_level := $(firstword $(BOARD_API_LEVEL) $(BOARD_SHIPPING_API_LEVEL))
+  ifneq (,$(board_api_level))
+    ifeq (true,$(call math_lt,$(board_api_level),31))
+      ENABLE_UFFD_GC := false
+    endif
+  endif
+
+  ifneq (,$(PRODUCT_SHIPPING_API_LEVEL))
+    ifeq (true,$(call math_lt,$(PRODUCT_SHIPPING_API_LEVEL),31))
+      ENABLE_UFFD_GC := false
+    endif
+  endif
+else ifeq (true,$(config_enable_uffd_gc))
+  ENABLE_UFFD_GC := true
+else ifeq (false,$(config_enable_uffd_gc))
+  ENABLE_UFFD_GC := false
+else
+  $(error Unknown PRODUCT_ENABLE_UFFD_GC value: $(config_enable_uffd_gc))
+endif
+
+ADDITIONAL_PRODUCT_PROPERTIES += ro.dalvik.vm.enable_uffd_gc=$(ENABLE_UFFD_GC)

core/dex_preopt_config.mk

@@ -130,6 +130,7 @@ ifeq ($(WRITE_SOONG_VARIABLES),true)
   $(call add_json_str,  Dex2oatXmx,                              $(DEX2OAT_XMX))
   $(call add_json_str,  Dex2oatXms,                              $(DEX2OAT_XMS))
   $(call add_json_str,  EmptyDirectory,                          $(OUT_DIR)/empty)
+  $(call add_json_bool, EnableUffdGc,                            $(ENABLE_UFFD_GC))
 
 ifdef TARGET_ARCH
   $(call add_json_map,  CpuVariant)

core/main.mk

@@ -493,6 +493,8 @@ endif
 # Typical build; include any Android.mk files we can find.
 #
 
+include $(BUILD_SYSTEM)/art_config.mk
+
 # Bring in dex_preopt.mk
 # This creates some modules so it needs to be included after
 # should-install-to-system is defined (in order for base_rules.mk to function

core/product.mk

@@ -370,6 +370,18 @@ _product_single_value_vars += PRODUCT_MODULE_BUILD_FROM_SOURCE
 # If true, installs a full version of com.android.virt APEX.
 _product_single_value_vars += PRODUCT_AVF_ENABLED
 
+# Whether to use userfaultfd GC.
+# Possible values are:
+# - "default" or empty: both the build system and the runtime determine whether to use userfaultfd
+#   GC based on the vendor API level
+# - "true": forces the build system to use userfaultfd GC regardless of the vendor API level; the
+#   runtime determines whether to use userfaultfd GC based on the kernel support. Note that the
+#   device may have to re-compile everything on the first boot if the kernel doesn't support
+#   userfaultfd
+# - "false": disallows the build system and the runtime to use userfaultfd GC even if the device
+#   supports it
+_product_single_value_vars += PRODUCT_ENABLE_UFFD_GC
+
 .KATI_READONLY := _product_single_value_vars _product_list_vars
 _product_var_list :=$= $(_product_single_value_vars) $(_product_list_vars)
 

core/soong_config.mk

@@ -9,6 +9,7 @@ BINDER32BIT := true
 endif
 endif
 
+include $(BUILD_SYSTEM)/art_config.mk
 include $(BUILD_SYSTEM)/dex_preopt_config.mk
 
 ifeq ($(WRITE_SOONG_VARIABLES),true)

target/product/default_art_config.mk

@@ -113,3 +113,5 @@ PRODUCT_SYSTEM_PROPERTIES += \
     dalvik.vm.image-dex2oat-Xmx=64m \
     dalvik.vm.dex2oat-Xms=64m \
     dalvik.vm.dex2oat-Xmx=512m \
+
+PRODUCT_ENABLE_UFFD_GC := false  # TODO(jiakaiz): Change this to "default".