LibC+LibELF: Implement more fully-features dlfcn functionality

This implements more of the dlfcn functionality. Most notably:

* It's now possible to dlopen() libraries which were already
  loaded at program startup time. This does not cause those
  libraries to be loaded twice.
* Errors are reported via dlerror() rather than by crashing
  the program.
* Calls to the dl*() functions are thread-safe.

1 files changed, 6 insertions, 89 deletions

diff --git a/Userland/Libraries/LibC/dlfcn.cpp b/Userland/Libraries/LibC/dlfcn.cpp
index 4e775b9465..73e54df798 100644
--- a/Userland/Libraries/LibC/dlfcn.cpp
+++ b/Userland/Libraries/LibC/dlfcn.cpp
@@ -1,95 +1,12 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Gunnar Beutner <gunnar@beutner.name>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/HashMap.h>
-#include <AK/LexicalPath.h>
-#include <AK/RefPtr.h>
-#include <AK/ScopeGuard.h>
-#include <AK/String.h>
-#include <LibELF/DynamicLoader.h>
-#include <assert.h>
-#include <dlfcn.h>
-#include <fcntl.h>
-#include <unistd.h>
+#include <LibDl/dlfcn_integration.h>
 
-// NOTE: The string here should never include a trailing newline (according to POSIX)
-String g_dlerror_msg;
-
-HashMap<String, RefPtr<ELF::DynamicLoader>> g_elf_objects;
-
-extern "C" {
-
-int dlclose(void*)
-{
-    g_dlerror_msg = "dlclose not implemented!";
-    return -1;
-}
-
-char* dlerror()
-{
-    return const_cast<char*>(g_dlerror_msg.characters());
-}
-
-void* dlopen(const char* filename, int flags)
-{
-    // FIXME: Create a global mutex/semaphore/lock for dlopen/dlclose/dlsym and (?) dlerror
-    // FIXME: refcount?
-
-    if (!filename) {
-        // FIXME: Return the handle for "the main executable"
-        //     The Serenity Kernel will keep a mapping of the main elf binary resident in memory,
-        //     But a future dynamic loader might have a different idea/way of letting us access this information
-        TODO();
-    }
-
-    auto basename = LexicalPath(filename).basename();
-
-    auto existing_elf_object = g_elf_objects.get(basename);
-    if (existing_elf_object.has_value()) {
-        return const_cast<ELF::DynamicLoader*>(existing_elf_object.value());
-    }
-
-    int fd = open(filename, O_RDONLY);
-    if (fd < 0) {
-        g_dlerror_msg = String::formatted("Unable to open file {}", filename);
-        return nullptr;
-    }
-
-    ScopeGuard close_fd_guard([fd]() { close(fd); });
-
-    auto loader = ELF::DynamicLoader::try_create(fd, filename);
-    if (!loader || !loader->is_valid()) {
-        g_dlerror_msg = String::formatted("{} is not a valid ELF dynamic shared object!", filename);
-        return nullptr;
-    }
-
-    auto object = loader->map();
-    if (!object || !loader->link(flags, /* total_tls_size (FIXME) */ 0)) {
-        g_dlerror_msg = String::formatted("Failed to load ELF object {}", filename);
-        return nullptr;
-    }
-
-    g_elf_objects.set(basename, move(loader));
-    g_dlerror_msg = "Successfully loaded ELF object.";
-
-    // we have one refcount already
-    return const_cast<ELF::DynamicLoader*>(g_elf_objects.get(basename).value());
-}
-
-void* dlsym(void* handle, const char* symbol_name)
-{
-    // FIXME: When called with a NULL handle we're supposed to search every dso in the process... that'll get expensive
-    VERIFY(handle);
-    auto* dso = reinterpret_cast<ELF::DynamicLoader*>(handle);
-    void* symbol = dso->symbol_for_name(symbol_name);
-    if (!symbol) {
-        g_dlerror_msg = "Symbol not found";
-        return nullptr;
-    }
-    return symbol;
-}
-
-} // extern "C"
+// These are used by libdl and are filled in by the dynamic loader.
+DlCloseFunction __dlclose;
+DlOpenFunction __dlopen;
+DlSymFunction __dlsym;