Add (for now, hardcoded) chainloader libraries

src/chainloader/vst2-chainloader.cpp

@@ -0,0 +1,105 @@
+// yabridge: a Wine plugin bridge
+// Copyright (C) 2020-2022 Robbert van der Helm
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+#include <atomic>
+#include <cassert>
+#include <mutex>
+
+#include <dlfcn.h>
+
+#include "../common/linking.h"
+#include "../common/utils.h"
+
+// These chainloader libraries are tiny, mostly dependencyless libraries that
+// `dlopen()` the actual `libyabridge-{vst2,vst3}.so` files and forward the
+// entry point function calls from this library to those. Or technically, these
+// libraries use dedicated entry point functions because multiple chainloader
+// libraries may all dynamically link to the exact same plugin library, so we
+// can't store any bridge information in a global there. This approach avoids
+// wasting disk space on copies on file systems that don't support reflinking,
+// but more importantly it also avoids the need to rerun `yabridgectl sync`
+// whenever yabridge is updated. This is even more important when considering
+// distro packaging, because updates to Boost might require the package to be
+// rebuilt, which in turn would also require a resync.
+
+// TODO: Order to check in: See Discord
+
+namespace fs = ghc::filesystem;
+
+using audioMasterCallback = void*;
+using AEffect = void;
+
+// These functions are loaded from `libyabridge-vst3.so` the first time
+// `VSTPluginMain` gets called
+AEffect* (*yabridge_plugin_init)(audioMasterCallback host_callback,
+                                 const char* plugin_path) = nullptr;
+
+/**
+ * The first time one of the exported functions from this library gets called,
+ * we'll need to load the corresponding `libyabridge-*.so` file and fetch the
+ * the entry point functions from that file.
+ */
+bool initialize_library() {
+    static void* library_handle = nullptr;
+    static std::mutex library_handle_mutex;
+
+    std::lock_guard lock(library_handle_mutex);
+
+    // There should be no situation where this library gets loaded and then two
+    // threads immediately start calling functions, but we'll handle that
+    // situation just in case it does happen
+    if (library_handle) {
+        return true;
+    }
+
+    // FIXME: Hardcoded path
+    library_handle = dlopen(
+        "/home/robbert/Documenten/projecten/yabridge/build/libyabridge-vst2.so",
+        RTLD_LAZY | RTLD_LOCAL);
+    assert(library_handle);
+
+#define LOAD_FUNCTION(name)                                                 \
+    do {                                                                    \
+        (name) =                                                            \
+            reinterpret_cast<decltype(name)>(dlsym(library_handle, #name)); \
+        assert(name);                                                       \
+    } while (false)
+
+    LOAD_FUNCTION(yabridge_plugin_init);
+
+#undef LOAD_FUNCTION
+
+    return true;
+}
+
+extern "C" YABRIDGE_EXPORT AEffect* VSTPluginMain(
+    audioMasterCallback host_callback) {
+    assert(host_callback);
+
+    initialize_library();
+
+    const fs::path this_plugin_path = get_this_file_location();
+    return yabridge_plugin_init(host_callback, this_plugin_path.c_str());
+}
+
+// XXX: GCC doens't seem to have a clean way to let you define an arbitrary
+//      function called 'main'. Even JUCE does it this way, so it should be
+//      safe.
+extern "C" YABRIDGE_EXPORT AEffect* deprecated_main(
+    audioMasterCallback audioMaster) asm("main");
+YABRIDGE_EXPORT AEffect* deprecated_main(audioMasterCallback audioMaster) {
+    return VSTPluginMain(audioMaster);
+}