Prevent statically linking to a lib providing stable C APIs

A lib providing stable C APIs should be available only to the APEX
containing the library. It shouldn't be available to other APEXes,
especially via static linking.

This change also fixes a bug that llndkImplDep (the dependency from
llndk stub to its implementation library) was recognized as being in the
same APEX.

Bug: 151051671
Test: m
Change-Id: Ifda7f4a367f68afcde93c86cda45a28cacd91f99

apex/apex.go

@@ -1858,6 +1858,44 @@ func (a *apexBundle) checkUpdatable(ctx android.ModuleContext) {
 	}
 }
 
+// Ensures that a lib providing stub isn't statically linked
+func (a *apexBundle) checkStaticLinkingToStubLibraries(ctx android.ModuleContext) {
+	// Practically, we only care about regular APEXes on the device.
+	if ctx.Host() || a.testApex || a.vndkApex {
+		return
+	}
+
+	a.walkPayloadDeps(ctx, func(ctx android.ModuleContext, from blueprint.Module, to android.ApexModule, externalDep bool) bool {
+		if ccm, ok := to.(*cc.Module); ok {
+			apexName := ctx.ModuleName()
+			fromName := ctx.OtherModuleName(from)
+			toName := ctx.OtherModuleName(to)
+
+			// If `to` is not actually in the same APEX as `from` then it does not need apex_available and neither
+			// do any of its dependencies.
+			if am, ok := from.(android.DepIsInSameApex); ok && !am.DepIsInSameApex(ctx, to) {
+				// As soon as the dependency graph crosses the APEX boundary, don't go further.
+				return false
+			}
+
+			// The dynamic linker and crash_dump tool in the runtime APEX is the only exception to this rule.
+			// It can't make the static dependencies dynamic because it can't
+			// do the dynamic linking for itself.
+			if apexName == "com.android.runtime" && (fromName == "linker" || fromName == "crash_dump") {
+				return false
+			}
+
+			isStubLibraryFromOtherApex := ccm.HasStubsVariants() && !android.DirectlyInApex(apexName, toName)
+			if isStubLibraryFromOtherApex && !externalDep {
+				ctx.ModuleErrorf("%q required by %q is a native library providing stub. "+
+					"It shouldn't be included in this APEX via static linking. Dependency path: %s", to.String(), fromName, ctx.GetPathString(false))
+			}
+
+		}
+		return true
+	})
+}
+
 func (a *apexBundle) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 	buildFlattenedAsDefault := ctx.Config().FlattenApex() && !ctx.Config().UnbundledBuild()
 	switch a.properties.ApexType {
@@ -1895,6 +1933,7 @@ func (a *apexBundle) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 
 	a.checkApexAvailability(ctx)
 	a.checkUpdatable(ctx)
+	a.checkStaticLinkingToStubLibraries(ctx)
 
 	handleSpecialLibs := !android.Bool(a.properties.Ignore_system_library_special_case)