Adjust the dladdr-based introspection logic used in art::GetAndroidRootSafe.

This logic originally assumed that the libartbase library linked into
the current binary was always located in a directory within the
Android Root. This is no longer true on target since libartbase moved
to the Runtime APEX; therefore we now only use that logic on host in
art::GetAndroidRootSafe.

Eventually we should be able to use this logic on target to find the
Android Runtime Root (in art::GetAndroidRuntimeRootSafe), as
libartbase is installed in the Runtime APEX. However, this is not
always true at the moment, as ART gtests still install another copy of
libartbase in /system/lib(64) (the Android Root) on target.

Also improve the documentation of methods `art::GetAndroidRoot(Safe)`
and `art::GetAndroidRuntimeRoot(Safe)`.

Test: m test-art-host-gtest-file_utils_test
Bug: 121117762
Bug: 129534335
Change-Id: I835207110dae0a550c06ac98ed4915241cc61c6f

1 files changed, 15 insertions, 0 deletions

diff --git a/libartbase/base/file_utils.h b/libartbase/base/file_utils.h
index 92b09c98c0..2115e954f8 100644
--- a/libartbase/base/file_utils.h
+++ b/libartbase/base/file_utils.h
@@ -29,11 +29,26 @@ namespace art {
 
 bool ReadFileToString(const std::string& file_name, std::string* result);
 
+// These methods return the Android Root, which is the historical location of
+// the Android "system" directory, containing the built Android artifacts. On
+// target, this is normally "/system". On host this is usually a directory under
+// the build tree, e.g. "$ANDROID_BUILD_TOP/out/host/linux-x86". The location of
+// the Android Root can be overriden using the ANDROID_ROOT environment
+// variable.
+//
 // Find $ANDROID_ROOT, /system, or abort.
 std::string GetAndroidRoot();
 // Find $ANDROID_ROOT, /system, or return an empty string.
 std::string GetAndroidRootSafe(/*out*/ std::string* error_msg);
 
+// These methods return the Android Runtime Root, which is the location of the
+// (activated) Android Runtime APEX module. On target, this is normally
+// "/apex/com.android.runtime". On host, this is usually a subdirectory of the
+// Android Root, e.g.
+// "$ANDROID_BUILD_TOP/out/host/linux-x86/com.android.runtime". The location of
+// the Android Runtime Root can be overriden using the ANDROID_RUNTIME_ROOT
+// environment variable.
+//
 // Find $ANDROID_RUNTIME_ROOT, /apex/com.android.runtime, or abort.
 std::string GetAndroidRuntimeRoot();
 // Find $ANDROID_RUNTIME_ROOT, /apex/com.android.runtime, or return an empty string.