LibC: Use LibELF in dlfcn.cpp to dynamically load libraries

Author: https://github.com/ADKaster
Commit: https://github.com/SerenityOS/serenity/commit/58517bc0682
Pull-request: https://github.com/SerenityOS/serenity/pull/954
Reviewed-by: https://github.com/awesomekling

Libraries/LibC/Makefile

@@ -56,7 +56,11 @@ LIBC_OBJS = \
        syslog.o \
        cxxabi.o
 
-OBJS = $(AK_OBJS) $(LIBC_OBJS)
+ELF_OBJS = \
+        ../LibELF/ELFDynamicObject.o \
+        ../LibELF/ELFImage.o
+
+OBJS = $(AK_OBJS) $(LIBC_OBJS) $(ELF_OBJS)
 
 EXTRA_OBJS = setjmp.ao crti.ao crtn.ao
 

Libraries/LibC/dlfcn.cpp

@@ -1,29 +1,103 @@
 #include <assert.h>
 #include <dlfcn.h>
+#include <fcntl.h>
+#include <mman.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+
+#include <AK/FileSystemPath.h>
+#include <AK/HashMap.h>
+#include <AK/RefPtr.h>
+#include <AK/ScopeGuard.h>
+#include <AK/String.h>
+#include <AK/StringBuilder.h>
+#include <LibELF/ELFDynamicObject.h>
+
+// NOTE: The string here should never include a trailing newline (according to POSIX)
+String g_dlerror_msg;
+
+HashMap<String, RefPtr<ELFDynamicObject>> g_elf_objects;
 
 extern "C" {
 
 int dlclose(void*)
 {
-    ASSERT_NOT_REACHED();
-    return 0;
+    g_dlerror_msg = "dlclose not implemented!";
+    return -1;
 }
 
 char* dlerror()
 {
-    ASSERT_NOT_REACHED();
-    return nullptr;
+    return const_cast<char*>(g_dlerror_msg.characters());
 }
 
-void* dlopen(const char*, int)
+void* dlopen(const char* filename, int flags)
 {
-    ASSERT_NOT_REACHED();
-    return nullptr;
+    // 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
+        ASSERT_NOT_REACHED();
+    }
+
+    FileSystemPath file_path(filename);
+
+    auto existing_elf_object = g_elf_objects.get(file_path.basename());
+    if (existing_elf_object.has_value()) {
+        void* referenced_object = existing_elf_object.value().leak_ref();
+        return referenced_object;
+    }
+
+    int fd = open(filename, O_RDONLY);
+    if (!fd) {
+        g_dlerror_msg = String::format("Unable to open file %s", filename);
+        return nullptr;
+    }
+
+    ScopeGuard close_fd_guard([fd]() { close(fd); });
+
+    struct stat file_stats{};
+
+    int ret = fstat(fd, &file_stats);
+    if (ret < 0) {
+        g_dlerror_msg = String::format("Unable to stat file %s", filename);
+        return nullptr;
+    }
+
+    auto image = ELFDynamicObject::construct(filename, fd, file_stats.st_size);
+
+    if (!image->is_valid()) {
+        g_dlerror_msg = String::format("%s is not a valid ELF dynamic shared object!", filename);
+        return nullptr;
+    }
+
+    if (!image->load(flags)) {
+        g_dlerror_msg = String::format("Failed to load ELF object %s", filename);
+        return nullptr;
+    }
+
+    g_elf_objects.set(file_path.basename(), move(image));
+    g_dlerror_msg = "Successfully loaded ELF object.";
+
+    // we have one refcount already
+    return g_elf_objects.get(file_path.basename()).value().ptr();
 }
 
-void* dlsym(void*, const char*)
+void* dlsym(void* handle, const char* symbol_name)
 {
-    ASSERT_NOT_REACHED();
-    return nullptr;
-}
+    // FIXME: When called with a NULL handle we're supposed to search every dso in the process... that'll get expensive
+    ASSERT(handle);
+    auto* dso = reinterpret_cast<ELFDynamicObject*>(handle);
+    void* symbol = dso->symbol_for_name(symbol_name);
+    if (!symbol) {
+        g_dlerror_msg = "Symbol not found";
+        return nullptr;
+    }
+    return symbol;
 }
+
+} // extern "C"