add libvndksupport

libvndksupport is a new LL-NDK library that provides vendor-visible APIs
for platform-only functionalities of other LL-NDK libraries. Currently,
it provides android_(load|unload)_sphal_library which abstracts the
platform-only APIs of libdl (android_get_exported_namespace, etc.)

Bug: 37323945
Test: sailfish builds and boots
Test: libvndksupport-tests passes

Merged-In: I6d2911b57e009d0c842554933aac87d6573ffcbf
Change-Id: I6d2911b57e009d0c842554933aac87d6573ffcbf
(cherry picked from commit 7130e13262)

libvndksupport/Android.bp

@@ -0,0 +1,15 @@
+subdirs = ["tests"]
+
+cc_library_shared {
+    name: "libvndksupport",
+    srcs: ["linker.c"],
+    local_include_dirs: ["include/vndksupport"],
+    export_include_dirs: ["include"],
+    shared_libs: ["liblog"],
+}
+
+llndk_library {
+    name: "libvndksupport",
+    symbol_file: "libvndksupport.map.txt",
+    export_include_dirs: ["include"],
+}

libvndksupport/include/vndksupport/linker.h

@@ -0,0 +1,31 @@
+/*
+ * 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.
+ */
+#ifndef VNDKSUPPORT_LINKER_H_
+#define VNDKSUPPORT_LINKER_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void* android_load_sphal_library(const char* name, int flag);
+
+int android_unload_sphal_library(void* handle);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // VNDKSUPPORT_LINKER_H_

libvndksupport/libvndksupport.map.txt

@@ -0,0 +1,7 @@
+LIBVNDKSUPPORT {
+  global:
+    android_load_sphal_library; # vndk
+    android_unload_sphal_library; # vndk
+  local:
+    *;
+};

libvndksupport/linker.c

@@ -0,0 +1,50 @@
+/*
+ * 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>
+
+extern struct android_namespace_t* android_get_exported_namespace(const char*);
+
+void* android_load_sphal_library(const char* name, int flag) {
+    struct android_namespace_t* sphal_namespace = android_get_exported_namespace("sphal");
+    if (sphal_namespace != NULL) {
+        const android_dlextinfo dlextinfo = {
+            .flags = ANDROID_DLEXT_USE_NAMESPACE, .library_namespace = sphal_namespace,
+        };
+        void* handle = android_dlopen_ext(name, flag, &dlextinfo);
+        if (handle) {
+            return handle;
+        } else {
+            ALOGW(
+                "Could not load %s from sphal namespace: %s. "
+                "Falling back to loading it from the current namespace,",
+                name, dlerror());
+        }
+    } else {
+        ALOGI(
+            "sphal namespace is not configured for this process. "
+            "Loading %s from the current namespace instead.",
+            name);
+    }
+    return dlopen(name, flag);
+}
+
+int android_unload_sphal_library(void* handle) { return dlclose(handle); }

libvndksupport/tests/Android.bp

@@ -0,0 +1,26 @@
+// 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.
+
+cc_test {
+    name: "libvndksupport-tests",
+    srcs: [
+        "linker_test.cpp",
+    ],
+
+    host_supported: false,
+    shared_libs: [
+        "libvndksupport",
+        "libbase",
+    ]
+}

libvndksupport/tests/linker_test.cpp

@@ -0,0 +1,60 @@
+/*
+ * 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 <gtest/gtest.h>
+
+#include <android-base/strings.h>
+#include <dirent.h>
+#include <dlfcn.h>
+#include <vndksupport/linker.h>
+#include <string>
+
+// Since the test executable will be in /data and ld.config.txt does not
+// configure sphal namespace for executables in /data, the call to
+// android_load_sphal_library will always fallback to the plain dlopen from the
+// default namespace.
+
+// Let's use libEGL_<chipset>.so as a SP-HAL in test
+static std::string find_sphal_lib() {
+    const char* path =
+#if defined(__LP64__)
+        "/vendor/lib64/egl";
+#else
+        "/vendor/lib/egl";
+#endif
+    std::unique_ptr<DIR, decltype(&closedir)> dir(opendir(path), closedir);
+
+    dirent* dp;
+    while ((dp = readdir(dir.get())) != nullptr) {
+        std::string name = dp->d_name;
+        if (android::base::StartsWith(name, "libEGL_")) {
+            return std::string(path) + "/" + name;
+        }
+    }
+    return "";
+}
+
+TEST(linker, load_existing_lib) {
+    std::string name = find_sphal_lib();
+    ASSERT_NE("", name);
+    void* handle = android_load_sphal_library(name.c_str(), RTLD_NOW | RTLD_LOCAL);
+    ASSERT_NE(nullptr, handle);
+    android_unload_sphal_library(handle);
+}
+
+TEST(linker, load_nonexisting_lib) {
+    void* handle = android_load_sphal_library("libNeverUseThisName.so", RTLD_NOW | RTLD_LOCAL);
+    ASSERT_EQ(nullptr, handle);
+}