init: adding fallback paths for debug ramdisk

Currently the gki_4_19_pixel5 presubmit test uses an old
vendor_boot-debug.img from a release branch. Adding fallback
paths to load debug resources from /first_stage_ramdisk dir to
pass the presubmit.

This CL should be reverted later once the vendor_boot-debug.img
gets updated to store the debug resources on the root dir.

Bug: 186082603
Test: boot a device with boot-debug.img
Test: boot a device with vendor_boot-debug.img
Change-Id: I9fcd77fc5a60a15cff254e432e05f1c9122ad80d
diff --git a/init/first_stage_init.cpp b/init/first_stage_init.cpp
index 78e5b60..84cda98 100644
--- a/init/first_stage_init.cpp
+++ b/init/first_stage_init.cpp
@@ -329,10 +329,23 @@
 
     // If "/force_debuggable" is present, the second-stage init will use a userdebug
     // sepolicy and load adb_debug.prop to allow adb root, if the device is unlocked.
+    bool found_debuggable = false;
+    std::string adb_debug_prop("/adb_debug.prop");
+    std::string userdebug_sepolicy("/userdebug_plat_sepolicy.cil");
     if (access("/force_debuggable", F_OK) == 0) {
+        found_debuggable = true;
+    } else if (access("/first_stage_ramdisk/force_debuggable", F_OK) == 0) {
+        // Fallback to legacy debug resource paths.
+        // TODO(b/186485355): removes the fallback path once it is not needed.
+        found_debuggable = true;
+        adb_debug_prop.insert(0, "/first_stage_ramdisk");
+        userdebug_sepolicy.insert(0, "/first_stage_ramdisk");
+    }
+
+    if (found_debuggable) {
         std::error_code ec;  // to invoke the overloaded copy_file() that won't throw.
-        if (!fs::copy_file("/adb_debug.prop", kDebugRamdiskProp, ec) ||
-            !fs::copy_file("/userdebug_plat_sepolicy.cil", kDebugRamdiskSEPolicy, ec)) {
+        if (!fs::copy_file(adb_debug_prop, kDebugRamdiskProp, ec) ||
+            !fs::copy_file(userdebug_sepolicy, kDebugRamdiskSEPolicy, ec)) {
             LOG(ERROR) << "Failed to setup debug ramdisk";
         } else {
             // setenv for second-stage init to read above kDebugRamdisk* files.