Switch libvndksupport's linker.c to C++

Bug: none
Test: device boots
Change-Id: I64237006a7f903647c8d8f7ca681b1da23ac53a9
diff --git a/libvndksupport/linker.cpp b/libvndksupport/linker.cpp
new file mode 100644
index 0000000..057e5b197
--- /dev/null
+++ b/libvndksupport/linker.cpp
@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+#include "linker.h"
+
+#include <android/dlext.h>
+#include <dlfcn.h>
+
+#define LOG_TAG "vndksupport"
+#include <log/log.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+__attribute__((weak)) extern "C" struct android_namespace_t* android_get_exported_namespace(
+        const char*);
+__attribute__((weak)) extern "C" void* android_dlopen_ext(const char*, int,
+                                                          const android_dlextinfo*);
+
+static const char* namespace_name = NULL;
+
+static struct android_namespace_t* get_vendor_namespace() {
+    const char* namespace_names[] = {"sphal", "default", NULL};
+    static struct android_namespace_t* vendor_namespace = NULL;
+    if (vendor_namespace == NULL) {
+        int name_idx = 0;
+        while (namespace_names[name_idx] != NULL) {
+            if (android_get_exported_namespace != NULL) {
+                vendor_namespace = android_get_exported_namespace(namespace_names[name_idx]);
+            }
+            if (vendor_namespace != NULL) {
+                namespace_name = namespace_names[name_idx];
+                break;
+            }
+            name_idx++;
+        }
+    }
+    return vendor_namespace;
+}
+
+int android_is_in_vendor_process() {
+    // Special case init, since when init runs, ld.config.<ver>.txt hasn't been
+    // loaded (sysprop service isn't up for init to know <ver>).
+    if (getpid() == 1) {
+        return 0;
+    }
+    if (android_get_exported_namespace == NULL) {
+        ALOGD("android_get_exported_namespace() not available. Assuming system process.");
+        return 0;
+    }
+
+    // In vendor process, 'vndk' namespace is not visible, whereas in system
+    // process, it is.
+    return android_get_exported_namespace("vndk") == NULL;
+}
+
+void* android_load_sphal_library(const char* name, int flag) {
+    struct android_namespace_t* vendor_namespace = get_vendor_namespace();
+    if (vendor_namespace != NULL) {
+        const android_dlextinfo dlextinfo = {
+                .flags = ANDROID_DLEXT_USE_NAMESPACE,
+                .library_namespace = vendor_namespace,
+        };
+        void* handle = NULL;
+        if (android_dlopen_ext != NULL) {
+            handle = android_dlopen_ext(name, flag, &dlextinfo);
+        }
+        if (!handle) {
+            ALOGE("Could not load %s from %s namespace: %s.", name, namespace_name, dlerror());
+        }
+        return handle;
+    } else {
+        ALOGD("Loading %s from current namespace instead of sphal namespace.", name);
+        return dlopen(name, flag);
+    }
+}
+
+int android_unload_sphal_library(void* handle) {
+    return dlclose(handle);
+}