Add stubs variants for bionic libs

Bionic libs are part of the runtime APEX (com.android.runtime). In order
to be able to update the runtime APEX independetly from the platform, we
have to prevent things outside of the APEX from using bionic symbols
that are not guaranteed to be stable. Otherwise, platform could break
when a symbol is removed from the libs via the APEX update.

To achive this goal, this change adds stubs variant to the bionic libs.
With this, things outside of the runtime APEX (i.e. other APEXes and the
platform) are built with the stubs variants that provide only the
symbols that are guaranteed to be stable.

The set of symbols are basically the same as the symbols available to
NDK clients. However, there are a few additional symbols that are not
available for NDK but should be made available for platform components.
They are marked with "# apex" tag. Symbols with that tag are not exposed
to apps (via NDK stubs) or vendors (via LLNDK stubs).

Note that the stubs is a build-time only artifact. It is used just to
break the build when private symbols are used outside of the runtime
APEX. At runtime, the real library in the APEX is used.

Bug: 120266448
Test: m
Test: m bionic-unit-tests
Change-Id: I7b8d75830c81d7d7d54e2fca21a85b3417531b47

2 files changed, 17 insertions, 8 deletions

diff --git a/libdl/Android.bp b/libdl/Android.bp
index c4078a0c5..262da6c7d 100644
--- a/libdl/Android.bp
+++ b/libdl/Android.bp
@@ -100,6 +100,11 @@ cc_library {
     sanitize: {
         never: true,
     },
+
+    stubs: {
+        symbol_file: "libdl.map.txt",
+        versions: ["10000"],
+    },
 }
 
 ndk_library {
diff --git a/libdl/libdl.map.txt b/libdl/libdl.map.txt
index c5d1be4d0..15148276a 100644
--- a/libdl/libdl.map.txt
+++ b/libdl/libdl.map.txt
@@ -41,15 +41,19 @@ LIBC_OMR1 { # introduced=27
     __cfi_slowpath_diag;
 } LIBC_N;
 
+LIBC_Q { # introduced=29
+  global:
+    android_create_namespace; # apex
+    android_dlwarning; # apex
+    android_get_LD_LIBRARY_PATH; # apex
+    android_get_exported_namespace; # apex
+    android_init_anonymous_namespace; # apex
+    android_link_namespaces; # apex
+    android_set_application_target_sdk_version; # apex
+} LIBC_OMR1;
+
 LIBC_PLATFORM {
   global:
     __cfi_init;
-    android_dlwarning;
-    android_set_application_target_sdk_version;
-    android_get_LD_LIBRARY_PATH;
     android_update_LD_LIBRARY_PATH;
-    android_init_anonymous_namespace;
-    android_create_namespace;
-    android_link_namespaces;
-    android_get_exported_namespace;
-} LIBC_OMR1;
+} LIBC_Q;