SymbolServer: Add symbolication service for out-of-process ELF parsing

This patch adds SymbolServer, a service daemon that provides
symbolication of ELF binaries. It has a very simple IPC API at the
moment that only turns addresses into symbol names.

This can be used to implement symbolication without having to do
in-process ELF parsing yourself. :^)

Userland/Services/SymbolServer/ClientConnection.cpp

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/MappedFile.h>
+#include <LibELF/Image.h>
+#include <SymbolServer/ClientConnection.h>
+#include <SymbolServer/SymbolClientEndpoint.h>
+
+namespace SymbolServer {
+
+struct CachedELF {
+    NonnullRefPtr<MappedFile> mapped_file;
+    ELF::Image elf;
+};
+
+static HashMap<String, CachedELF> s_cache;
+static HashMap<int, RefPtr<ClientConnection>> s_connections;
+
+ClientConnection::ClientConnection(NonnullRefPtr<Core::LocalSocket> socket, int client_id)
+    : IPC::ClientConnection<SymbolClientEndpoint, SymbolServerEndpoint>(*this, move(socket), client_id)
+{
+    s_connections.set(client_id, *this);
+}
+
+ClientConnection::~ClientConnection()
+{
+}
+
+void ClientConnection::die()
+{
+    s_connections.remove(client_id());
+}
+
+OwnPtr<Messages::SymbolServer::GreetResponse> ClientConnection::handle(const Messages::SymbolServer::Greet&)
+{
+    return make<Messages::SymbolServer::GreetResponse>();
+}
+
+OwnPtr<Messages::SymbolServer::SymbolicateResponse> ClientConnection::handle(const Messages::SymbolServer::Symbolicate& message)
+{
+    auto path = message.path();
+    if (!s_cache.contains(path)) {
+        auto mapped_file = MappedFile::map(path);
+        if (mapped_file.is_error()) {
+            dbgln("Failed to map {}: {}", path, mapped_file.error().string());
+            return make<Messages::SymbolServer::SymbolicateResponse>(false, Vector<String> {});
+        }
+        auto elf = ELF::Image(mapped_file.value()->bytes());
+        if (!elf.is_valid()) {
+            dbgln("ELF not valid: {}", path);
+            return make<Messages::SymbolServer::SymbolicateResponse>(false, Vector<String> {});
+        }
+        auto cached_elf = CachedELF { mapped_file.release_value(), move(elf) };
+        s_cache.set(path, move(cached_elf));
+    }
+
+    auto it = s_cache.find(path);
+    ASSERT(it != s_cache.end());
+    auto& cached_elf = it->value;
+
+    Vector<String> symbols;
+    symbols.ensure_capacity(message.addresses().size());
+
+    for (auto address : message.addresses()) {
+        u32 offset = 0;
+        auto symbol = cached_elf.elf.symbolicate(address, &offset);
+        symbols.append(move(symbol));
+    }
+
+    return make<Messages::SymbolServer::SymbolicateResponse>(true, move(symbols));
+}
+
+}