Determine GC type based on BUILT_KERNEL_VERSION_FILE.

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

1 files changed, 68 insertions, 0 deletions

diff --git a/scripts/uffd_gc_utils.py b/scripts/uffd_gc_utils.py
new file mode 100644
index 000000000..2d35494dc
--- /dev/null
+++ b/scripts/uffd_gc_utils.py
@@ -0,0 +1,68 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2024 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+"""Utils to determine whether to enable UFFD GC."""
+
+import re
+import sys
+
+
+def should_enable_uffd_gc(kernel_version_file):
+  with open(kernel_version_file, 'r') as f:
+    kernel_version = f.read().strip()
+  return should_enable_uffd_gc_impl(kernel_version)
+
+def should_enable_uffd_gc_impl(kernel_version):
+  # See https://source.android.com/docs/core/architecture/kernel/gki-versioning#determine-release
+  p = r"^(?P<w>\d+)[.](?P<x>\d+)[.](?P<y>\d+)(-android(?P<z>\d+)-(?P<k>\d+).*$)?"
+  m = re.match(p, kernel_version)
+  if m is not None:
+    if m.group('z') is not None:
+      android_release = int(m.group('z'))
+      # No need to check w, x, y because all Android 12 kernels have backports.
+      return android_release >= 12
+    else:
+      # Old kernel or non-GKI kernel.
+      version = int(m.group('w'))
+      patch_level = int(m.group('x'))
+      if version < 5:
+        # Old kernel.
+        return False
+      elif (version == 5 and patch_level >= 7) or version >= 6:
+        # New non-GKI kernel. 5.7 supports MREMAP_DONTUNMAP without the need for
+        # backports.
+        return True
+      else:
+        # Non-GKI kernel between 5 and 5.6. It may have backports.
+        raise exit_with_error(kernel_version)
+  elif kernel_version == '<unknown-kernel>':
+    # The kernel information isn't available to the build system, probably
+    # because PRODUCT_OTA_ENFORCE_VINTF_KERNEL_REQUIREMENTS is set to false. We
+    # assume that the kernel supports UFFD GC because it is the case for most of
+    # the products today and it is the future.
+    return True
+  else:
+    # Unrecognizable non-GKI kernel.
+    raise exit_with_error(kernel_version)
+
+def exit_with_error(kernel_version):
+  sys.exit(f"""
+Unable to determine UFFD GC flag for kernel version "{kernel_version}".
+You can fix this by explicitly setting PRODUCT_ENABLE_UFFD_GC to "true" or
+"false" based on the kernel version.
+1. Set PRODUCT_ENABLE_UFFD_GC to "true" if the kernel supports userfaultfd(2)
+   and MREMAP_DONTUNMAP.
+2. Set PRODUCT_ENABLE_UFFD_GC to "false" otherwise.""")