Kernel: Simplify Process factory functions

- Instead of taking the first new thread as an out-parameter, we now
  bundle the process and its first thread in a struct and use that
  as the return value.

- Make all Process factory functions return ErrorOr. Use this to convert
  some places to more TRY().

- Drop the "try_" prefix on Process factory functions.

Kernel/Arch/aarch64/init.cpp

@@ -0,0 +1,255 @@
+/*
+ * Copyright (c) 2021, Nico Weber <thakis@chromium.org>
+ * Copyright (c) 2021, Marcin Undak <mcinek@gmail.com>
+ * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
+ * Copyright (c) 2022, the SerenityOS developers.
+ * Copyright (c) 2022, Filiph Sandström <filiph.sandstrom@filfatstudios.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Format.h>
+#include <AK/Types.h>
+
+#include <Kernel/Arch/InterruptManagement.h>
+#include <Kernel/Arch/Interrupts.h>
+#include <Kernel/Arch/Processor.h>
+#include <Kernel/Arch/aarch64/ASM_wrapper.h>
+#include <Kernel/Arch/aarch64/BootPPMParser.h>
+#include <Kernel/Arch/aarch64/CPU.h>
+#include <Kernel/Arch/aarch64/RPi/Framebuffer.h>
+#include <Kernel/Arch/aarch64/RPi/Mailbox.h>
+#include <Kernel/Arch/aarch64/RPi/UART.h>
+#include <Kernel/Arch/aarch64/Registers.h>
+#include <Kernel/Arch/aarch64/TrapFrame.h>
+#include <Kernel/CommandLine.h>
+#include <Kernel/Devices/DeviceManagement.h>
+#include <Kernel/FileSystem/VirtualFileSystem.h>
+#include <Kernel/Graphics/Console/BootFramebufferConsole.h>
+#include <Kernel/KSyms.h>
+#include <Kernel/Memory/MemoryManager.h>
+#include <Kernel/Panic.h>
+#include <Kernel/Scheduler.h>
+#include <Kernel/Storage/StorageManagement.h>
+#include <Kernel/TTY/VirtualConsole.h>
+
+typedef void (*ctor_func_t)();
+extern ctor_func_t start_heap_ctors[];
+extern ctor_func_t end_heap_ctors[];
+extern ctor_func_t start_ctors[];
+extern ctor_func_t end_ctors[];
+
+// FIXME: Share this with the Intel Prekernel.
+extern uintptr_t __stack_chk_guard;
+uintptr_t __stack_chk_guard;
+
+READONLY_AFTER_INIT bool g_in_early_boot;
+
+namespace Kernel {
+
+static void draw_logo(u8* framebuffer_data);
+static u32 query_firmware_version();
+
+extern "C" [[noreturn]] void halt();
+extern "C" [[noreturn]] void init();
+
+ALWAYS_INLINE static Processor& bootstrap_processor()
+{
+    alignas(Processor) static u8 bootstrap_processor_storage[sizeof(Processor)];
+    return (Processor&)bootstrap_processor_storage;
+}
+
+Atomic<Graphics::Console*> g_boot_console;
+
+VirtualConsole* tty0;
+ProcessID g_init_pid { 0 };
+
+static void init_stage2(void*);
+void init_stage2(void*)
+{
+    Process::register_new(Process::current());
+
+    auto firmware_version = query_firmware_version();
+    dmesgln("Firmware version: {}", firmware_version);
+
+    VirtualFileSystem::initialize();
+
+    StorageManagement::the().initialize(kernel_command_line().root_device(), kernel_command_line().is_force_pio(), kernel_command_line().is_nvme_polling_enabled());
+    if (VirtualFileSystem::the().mount_root(StorageManagement::the().root_filesystem()).is_error()) {
+        PANIC("VirtualFileSystem::mount_root failed");
+    }
+
+    // Switch out of early boot mode.
+    g_in_early_boot = false;
+
+    auto userspace_init = kernel_command_line().userspace_init();
+    auto init_args = kernel_command_line().userspace_init_args();
+
+    auto init_or_error = Process::create_user_process(userspace_init, UserID(0), GroupID(0), move(init_args), {}, tty0);
+    if (init_or_error.is_error())
+        PANIC("init_stage2: Error spawning init process: {}", init_or_error.error());
+
+    auto [init_process, init_thread] = init_or_error.release_value();
+    g_init_pid = init_process->pid();
+
+    init_thread->set_priority(THREAD_PRIORITY_HIGH);
+
+    Process::current().sys$exit(0);
+    VERIFY_NOT_REACHED();
+}
+
+extern "C" [[noreturn]] void init()
+{
+    g_in_early_boot = true;
+
+    // FIXME: Don't hardcode this
+    multiboot_memory_map_t mmap[] = {
+        { sizeof(struct multiboot_mmap_entry) - sizeof(u32),
+            (u64)0x0,
+            (u64)0x3F000000,
+            MULTIBOOT_MEMORY_AVAILABLE }
+    };
+
+    multiboot_memory_map = mmap;
+    multiboot_memory_map_count = 1;
+
+    dbgln("Welcome to Serenity OS!");
+    dbgln("Imagine this being your ideal operating system.");
+    dbgln("Observed deviations from that ideal are shortcomings of your imagination.");
+    dbgln();
+
+    CommandLine::early_initialize("");
+
+    new (&bootstrap_processor()) Processor();
+    bootstrap_processor().install(0);
+
+    // We call the constructors of kmalloc.cpp separately, because other constructors in the Kernel
+    // might rely on being able to call new/kmalloc in the constructor. We do have to run the
+    // kmalloc constructors, because kmalloc_init relies on that.
+    for (ctor_func_t* ctor = start_heap_ctors; ctor < end_heap_ctors; ctor++)
+        (*ctor)();
+    kmalloc_init();
+
+    bootstrap_processor().initialize();
+
+    load_kernel_symbol_table();
+
+    CommandLine::initialize();
+
+    dmesgln("Starting SerenityOS...");
+
+    Memory::MemoryManager::initialize(0);
+    DeviceManagement::initialize();
+    SysFSComponentRegistry::initialize();
+    DeviceManagement::the().attach_null_device(*NullDevice::must_initialize());
+
+    // Invoke all static global constructors in the kernel.
+    // Note that we want to do this as early as possible.
+    for (ctor_func_t* ctor = start_ctors; ctor < end_ctors; ctor++)
+        (*ctor)();
+
+    auto& framebuffer = RPi::Framebuffer::the();
+    if (framebuffer.initialized()) {
+        g_boot_console = &try_make_lock_ref_counted<Graphics::BootFramebufferConsole>(PhysicalAddress((PhysicalPtr)framebuffer.gpu_buffer()), framebuffer.width(), framebuffer.height(), framebuffer.pitch()).value().leak_ref();
+        draw_logo(static_cast<Graphics::BootFramebufferConsole*>(g_boot_console.load())->unsafe_framebuffer_data());
+    }
+
+    initialize_interrupts();
+    InterruptManagement::initialize();
+    Processor::enable_interrupts();
+
+    // Note: We have to disable interrupts otherwise Scheduler::timer_tick might be called before the scheduler is started.
+    Processor::disable_interrupts();
+    TimeManagement::initialize(0);
+
+    Process::initialize();
+    Scheduler::initialize();
+
+    MUST(Process::create_kernel_process(KString::must_create("init_stage2"sv), init_stage2, nullptr, THREAD_AFFINITY_DEFAULT, Process::RegisterProcess::No));
+
+    Scheduler::start();
+
+    VERIFY_NOT_REACHED();
+}
+
+class QueryFirmwareVersionMboxMessage : RPi::Mailbox::Message {
+public:
+    u32 version;
+
+    QueryFirmwareVersionMboxMessage()
+        : RPi::Mailbox::Message(0x0000'0001, 4)
+    {
+        version = 0;
+    }
+};
+
+static u32 query_firmware_version()
+{
+    struct __attribute__((aligned(16))) {
+        RPi::Mailbox::MessageHeader header;
+        QueryFirmwareVersionMboxMessage query_firmware_version;
+        RPi::Mailbox::MessageTail tail;
+    } message_queue;
+
+    if (!RPi::Mailbox::the().send_queue(&message_queue, sizeof(message_queue))) {
+        return 0xffff'ffff;
+    }
+
+    return message_queue.query_firmware_version.version;
+}
+
+extern "C" const u32 serenity_boot_logo_start;
+extern "C" const u32 serenity_boot_logo_size;
+
+static void draw_logo(u8* framebuffer_data)
+{
+    BootPPMParser logo_parser(reinterpret_cast<u8 const*>(&serenity_boot_logo_start), serenity_boot_logo_size);
+    if (!logo_parser.parse()) {
+        dbgln("Failed to parse boot logo.");
+        return;
+    }
+
+    dbgln("Boot logo size: {} ({} x {})", serenity_boot_logo_size, logo_parser.image.width, logo_parser.image.height);
+
+    auto& framebuffer = RPi::Framebuffer::the();
+    auto fb_ptr = framebuffer_data;
+    auto image_left = (framebuffer.width() - logo_parser.image.width) / 2;
+    auto image_right = image_left + logo_parser.image.width;
+    auto image_top = (framebuffer.height() - logo_parser.image.height) / 2;
+    auto image_bottom = image_top + logo_parser.image.height;
+    auto logo_pixels = logo_parser.image.pixel_data;
+
+    for (u32 y = 0; y < framebuffer.height(); y++) {
+        for (u32 x = 0; x < framebuffer.width(); x++) {
+            if (x >= image_left && x < image_right && y >= image_top && y < image_bottom) {
+                switch (framebuffer.pixel_order()) {
+                case RPi::Framebuffer::PixelOrder::RGB:
+                    fb_ptr[0] = logo_pixels[0];
+                    fb_ptr[1] = logo_pixels[1];
+                    fb_ptr[2] = logo_pixels[2];
+                    break;
+                case RPi::Framebuffer::PixelOrder::BGR:
+                    fb_ptr[0] = logo_pixels[2];
+                    fb_ptr[1] = logo_pixels[1];
+                    fb_ptr[2] = logo_pixels[0];
+                    break;
+                default:
+                    dbgln("Unsupported pixel format");
+                    VERIFY_NOT_REACHED();
+                }
+
+                logo_pixels += 3;
+            } else {
+                fb_ptr[0] = 0xBD;
+                fb_ptr[1] = 0xBD;
+                fb_ptr[2] = 0xBD;
+            }
+
+            fb_ptr[3] = 0xFF;
+            fb_ptr += 4;
+        }
+        fb_ptr += framebuffer.pitch() - framebuffer.width() * 4;
+    }
+}
+
+}

Kernel/Arch/init.cpp

@@ -281,13 +281,7 @@ extern "C" [[noreturn]] UNMAP_AFTER_INIT void init([[maybe_unused]] BootInfo con
     }
 #endif
 
-    {
-        LockRefPtr<Thread> init_stage2_thread;
-        (void)Process::create_kernel_process(init_stage2_thread, KString::must_create("init_stage2"sv), init_stage2, nullptr, THREAD_AFFINITY_DEFAULT, Process::RegisterProcess::No);
-        // We need to make sure we drop the reference for init_stage2_thread
-        // before calling into Scheduler::start, otherwise we will have a
-        // dangling Thread that never gets cleaned up
-    }
+    MUST(Process::create_kernel_process(KString::must_create("init_stage2"sv), init_stage2, nullptr, THREAD_AFFINITY_DEFAULT, Process::RegisterProcess::No));
 
     Scheduler::start();
     VERIFY_NOT_REACHED();
@@ -415,17 +409,17 @@ void init_stage2(void*)
     // NOTE: Everything marked UNMAP_AFTER_INIT becomes inaccessible after this point.
     MM.unmap_text_after_init();
 
-    LockRefPtr<Thread> thread;
     auto userspace_init = kernel_command_line().userspace_init();
     auto init_args = kernel_command_line().userspace_init_args();
 
-    auto init_or_error = Process::try_create_user_process(thread, userspace_init, UserID(0), GroupID(0), move(init_args), {}, tty0);
+    auto init_or_error = Process::create_user_process(userspace_init, UserID(0), GroupID(0), move(init_args), {}, tty0);
     if (init_or_error.is_error())
         PANIC("init_stage2: Error spawning init process: {}", init_or_error.error());
 
-    g_init_pid = init_or_error.value()->pid();
+    auto [init_process, init_thread] = init_or_error.release_value();
 
-    thread->set_priority(THREAD_PRIORITY_HIGH);
+    g_init_pid = init_process->pid();
+    init_thread->set_priority(THREAD_PRIORITY_HIGH);
 
     if (boot_profiling) {
         dbgln("Starting full system boot profiling");

Kernel/Bus/USB/UHCI/UHCIController.cpp

@@ -585,22 +585,20 @@ size_t UHCIController::poll_transfer_queue(QueueHead& transfer_queue)
 
 ErrorOr<void> UHCIController::spawn_port_process()
 {
-    LockRefPtr<Thread> usb_hotplug_thread;
-    (void)Process::create_kernel_process(usb_hotplug_thread, TRY(KString::try_create("UHCI Hot Plug Task"sv)), [&] {
+    TRY(Process::create_kernel_process(TRY(KString::try_create("UHCI Hot Plug Task"sv)), [&] {
         for (;;) {
             if (m_root_hub)
                 m_root_hub->check_for_port_updates();
 
             (void)Thread::current()->sleep(Time::from_seconds(1));
         }
-    });
+    }));
     return {};
 }
 
 ErrorOr<void> UHCIController::spawn_async_poll_process()
 {
-    LockRefPtr<Thread> async_poll_thread;
-    (void)Process::create_kernel_process(async_poll_thread, TRY(KString::try_create("UHCI Async Poll Task"sv)), [&] {
+    TRY(Process::create_kernel_process(TRY(KString::try_create("UHCI Async Poll Task"sv)), [&] {
         u16 poll_interval_ms = 1024;
         for (;;) {
             {
@@ -620,7 +618,7 @@ ErrorOr<void> UHCIController::spawn_async_poll_process()
             }
             (void)Thread::current()->sleep(Time::from_milliseconds(poll_interval_ms));
         }
-    });
+    }));
     return {};
 }
 

Kernel/FileSystem/Plan9FS/FileSystem.cpp

@@ -353,10 +353,11 @@ void Plan9FS::ensure_thread()
         auto process_name = KString::try_create("Plan9FS"sv);
         if (process_name.is_error())
             TODO();
-        (void)Process::create_kernel_process(m_thread, process_name.release_value(), [&]() {
+        auto [_, thread] = Process::create_kernel_process(process_name.release_value(), [&]() {
             thread_main();
             m_thread_running.store(false, AK::MemoryOrder::memory_order_release);
-        });
+        }).release_value_but_fixme_should_propagate_errors();
+        m_thread = move(thread);
     }
 }
 

Kernel/Net/NetworkTask.cpp

@@ -42,12 +42,11 @@ static HashTable<NonnullRefPtr<TCPSocket>>* delayed_ack_sockets;
 
 void NetworkTask::spawn()
 {
-    LockRefPtr<Thread> thread;
     auto name = KString::try_create("Network Task"sv);
     if (name.is_error())
         TODO();
-    (void)Process::create_kernel_process(thread, name.release_value(), NetworkTask_main, nullptr);
-    network_task = thread;
+    auto [_, first_thread] = MUST(Process::create_kernel_process(name.release_value(), NetworkTask_main, nullptr));
+    network_task = first_thread;
 }
 
 bool NetworkTask::is_current()

Kernel/Process.cpp

@@ -208,7 +208,7 @@ void Process::register_new(Process& process)
     });
 }
 
-ErrorOr<NonnullRefPtr<Process>> Process::try_create_user_process(LockRefPtr<Thread>& first_thread, StringView path, UserID uid, GroupID gid, Vector<NonnullOwnPtr<KString>> arguments, Vector<NonnullOwnPtr<KString>> environment, TTY* tty)
+ErrorOr<Process::ProcessAndFirstThread> Process::create_user_process(StringView path, UserID uid, GroupID gid, Vector<NonnullOwnPtr<KString>> arguments, Vector<NonnullOwnPtr<KString>> environment, TTY* tty)
 {
     auto parts = path.split_view('/');
     if (arguments.is_empty()) {
@@ -218,7 +218,7 @@ ErrorOr<NonnullRefPtr<Process>> Process::try_create_user_process(LockRefPtr<Thre
 
     auto path_string = TRY(KString::try_create(path));
     auto name = TRY(KString::try_create(parts.last()));
-    auto process = TRY(Process::try_create(first_thread, move(name), uid, gid, ProcessID(0), false, VirtualFileSystem::the().root_custody(), nullptr, tty));
+    auto [process, first_thread] = TRY(Process::create(move(name), uid, gid, ProcessID(0), false, VirtualFileSystem::the().root_custody(), nullptr, tty));
 
     TRY(process->m_fds.with_exclusive([&](auto& fds) -> ErrorOr<void> {
         TRY(fds.try_resize(Process::OpenFileDescriptions::max_open()));
@@ -238,11 +238,7 @@ ErrorOr<NonnullRefPtr<Process>> Process::try_create_user_process(LockRefPtr<Thre
 
     Thread* new_main_thread = nullptr;
     InterruptsState previous_interrupts_state = InterruptsState::Enabled;
-    if (auto result = process->exec(move(path_string), move(arguments), move(environment), new_main_thread, previous_interrupts_state); result.is_error()) {
-        dbgln("Failed to exec {}: {}", path, result.error());
-        first_thread = nullptr;
-        return result.release_error();
-    }
+    TRY(process->exec(move(path_string), move(arguments), move(environment), new_main_thread, previous_interrupts_state));
 
     register_new(*process);
 
@@ -254,25 +250,24 @@ ErrorOr<NonnullRefPtr<Process>> Process::try_create_user_process(LockRefPtr<Thre
         new_main_thread->set_state(Thread::State::Runnable);
     }
 
-    return process;
+    return ProcessAndFirstThread { move(process), move(first_thread) };
 }
 
-RefPtr<Process> Process::create_kernel_process(LockRefPtr<Thread>& first_thread, NonnullOwnPtr<KString> name, void (*entry)(void*), void* entry_data, u32 affinity, RegisterProcess do_register)
+ErrorOr<Process::ProcessAndFirstThread> Process::create_kernel_process(NonnullOwnPtr<KString> name, void (*entry)(void*), void* entry_data, u32 affinity, RegisterProcess do_register)
 {
-    auto process_or_error = Process::try_create(first_thread, move(name), UserID(0), GroupID(0), ProcessID(0), true);
-    if (process_or_error.is_error())
-        return {};
-    auto process = process_or_error.release_value();
+    auto process_and_first_thread = TRY(Process::create(move(name), UserID(0), GroupID(0), ProcessID(0), true));
+    auto& process = *process_and_first_thread.process;
+    auto& thread = *process_and_first_thread.first_thread;
 
-    first_thread->regs().set_entry_function((FlatPtr)entry, (FlatPtr)entry_data);
+    thread.regs().set_entry_function((FlatPtr)entry, (FlatPtr)entry_data);
 
     if (do_register == RegisterProcess::Yes)
-        register_new(*process);
+        register_new(process);
 
     SpinlockLocker lock(g_scheduler_lock);
-    first_thread->set_affinity(affinity);
-    first_thread->set_state(Thread::State::Runnable);
-    return process;
+    thread.set_affinity(affinity);
+    thread.set_state(Thread::State::Runnable);
+    return process_and_first_thread;
 }
 
 void Process::protect_data()
@@ -289,7 +284,7 @@ void Process::unprotect_data()
     });
 }
 
-ErrorOr<NonnullRefPtr<Process>> Process::try_create(LockRefPtr<Thread>& first_thread, NonnullOwnPtr<KString> name, UserID uid, GroupID gid, ProcessID ppid, bool is_kernel_process, RefPtr<Custody> current_directory, RefPtr<Custody> executable, TTY* tty, Process* fork_parent)
+ErrorOr<Process::ProcessAndFirstThread> Process::create(NonnullOwnPtr<KString> name, UserID uid, GroupID gid, ProcessID ppid, bool is_kernel_process, RefPtr<Custody> current_directory, RefPtr<Custody> executable, TTY* tty, Process* fork_parent)
 {
     OwnPtr<Memory::AddressSpace> new_address_space;
     if (fork_parent) {
@@ -303,9 +298,11 @@ ErrorOr<NonnullRefPtr<Process>> Process::try_create(LockRefPtr<Thread>& first_th
     auto unveil_tree = UnveilNode { TRY(KString::try_create("/"sv)), UnveilMetadata(TRY(KString::try_create("/"sv))) };
     auto exec_unveil_tree = UnveilNode { TRY(KString::try_create("/"sv)), UnveilMetadata(TRY(KString::try_create("/"sv))) };
     auto credentials = TRY(Credentials::create(uid, gid, uid, gid, uid, gid, {}, fork_parent ? fork_parent->sid() : 0, fork_parent ? fork_parent->pgid() : 0));
+
     auto process = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) Process(move(name), move(credentials), ppid, is_kernel_process, move(current_directory), move(executable), tty, move(unveil_tree), move(exec_unveil_tree))));
-    TRY(process->attach_resources(new_address_space.release_nonnull(), first_thread, fork_parent));
-    return process;
+    auto first_thread = TRY(process->attach_resources(new_address_space.release_nonnull(), fork_parent));
+
+    return ProcessAndFirstThread { move(process), move(first_thread) };
 }
 
 Process::Process(NonnullOwnPtr<KString> name, NonnullRefPtr<Credentials> credentials, ProcessID ppid, bool is_kernel_process, RefPtr<Custody> current_directory, RefPtr<Custody> executable, TTY* tty, UnveilNode unveil_tree, UnveilNode exec_unveil_tree)
@@ -332,7 +329,7 @@ Process::Process(NonnullOwnPtr<KString> name, NonnullRefPtr<Credentials> credent
     }
 }
 
-ErrorOr<void> Process::attach_resources(NonnullOwnPtr<Memory::AddressSpace>&& preallocated_space, LockRefPtr<Thread>& first_thread, Process* fork_parent)
+ErrorOr<NonnullLockRefPtr<Thread>> Process::attach_resources(NonnullOwnPtr<Memory::AddressSpace>&& preallocated_space, Process* fork_parent)
 {
     m_space.with([&](auto& space) {
         space = move(preallocated_space);
@@ -347,7 +344,7 @@ ErrorOr<void> Process::attach_resources(NonnullOwnPtr<Memory::AddressSpace>&& pr
         return Thread::try_create(*this);
     };
 
-    first_thread = TRY(create_first_thread());
+    auto first_thread = TRY(create_first_thread());
 
     if (!fork_parent) {
         // FIXME: Figure out if this is really necessary.
@@ -359,7 +356,7 @@ ErrorOr<void> Process::attach_resources(NonnullOwnPtr<Memory::AddressSpace>&& pr
     if (fork_parent)
         m_signal_action_data = fork_parent->m_signal_action_data;
 
-    return {};
+    return first_thread;
 }
 
 Process::~Process()

Kernel/Process.h

@@ -185,15 +185,20 @@ public:
         Yes
     };
 
+    struct ProcessAndFirstThread {
+        NonnullRefPtr<Process> process;
+        NonnullLockRefPtr<Thread> first_thread;
+    };
+
     template<typename EntryFunction>
-    static RefPtr<Process> create_kernel_process(LockRefPtr<Thread>& first_thread, NonnullOwnPtr<KString> name, EntryFunction entry, u32 affinity = THREAD_AFFINITY_DEFAULT, RegisterProcess do_register = RegisterProcess::Yes)
+    static ErrorOr<ProcessAndFirstThread> create_kernel_process(NonnullOwnPtr<KString> name, EntryFunction entry, u32 affinity = THREAD_AFFINITY_DEFAULT, RegisterProcess do_register = RegisterProcess::Yes)
     {
         auto* entry_func = new EntryFunction(move(entry));
-        return create_kernel_process(first_thread, move(name), &Process::kernel_process_trampoline<EntryFunction>, entry_func, affinity, do_register);
+        return create_kernel_process(move(name), &Process::kernel_process_trampoline<EntryFunction>, entry_func, affinity, do_register);
     }
 
-    static RefPtr<Process> create_kernel_process(LockRefPtr<Thread>& first_thread, NonnullOwnPtr<KString> name, void (*entry)(void*), void* entry_data = nullptr, u32 affinity = THREAD_AFFINITY_DEFAULT, RegisterProcess do_register = RegisterProcess::Yes);
-    static ErrorOr<NonnullRefPtr<Process>> try_create_user_process(LockRefPtr<Thread>& first_thread, StringView path, UserID, GroupID, Vector<NonnullOwnPtr<KString>> arguments, Vector<NonnullOwnPtr<KString>> environment, TTY*);
+    static ErrorOr<ProcessAndFirstThread> create_kernel_process(NonnullOwnPtr<KString> name, void (*entry)(void*), void* entry_data = nullptr, u32 affinity = THREAD_AFFINITY_DEFAULT, RegisterProcess do_register = RegisterProcess::Yes);
+    static ErrorOr<ProcessAndFirstThread> create_user_process(StringView path, UserID, GroupID, Vector<NonnullOwnPtr<KString>> arguments, Vector<NonnullOwnPtr<KString>> environment, TTY*);
     static void register_new(Process&);
 
     ~Process();
@@ -594,8 +599,8 @@ private:
     bool remove_thread(Thread&);
 
     Process(NonnullOwnPtr<KString> name, NonnullRefPtr<Credentials>, ProcessID ppid, bool is_kernel_process, RefPtr<Custody> current_directory, RefPtr<Custody> executable, TTY* tty, UnveilNode unveil_tree, UnveilNode exec_unveil_tree);
-    static ErrorOr<NonnullRefPtr<Process>> try_create(LockRefPtr<Thread>& first_thread, NonnullOwnPtr<KString> name, UserID, GroupID, ProcessID ppid, bool is_kernel_process, RefPtr<Custody> current_directory = nullptr, RefPtr<Custody> executable = nullptr, TTY* = nullptr, Process* fork_parent = nullptr);
-    ErrorOr<void> attach_resources(NonnullOwnPtr<Memory::AddressSpace>&&, LockRefPtr<Thread>& first_thread, Process* fork_parent);
+    static ErrorOr<ProcessAndFirstThread> create(NonnullOwnPtr<KString> name, UserID, GroupID, ProcessID ppid, bool is_kernel_process, RefPtr<Custody> current_directory = nullptr, RefPtr<Custody> executable = nullptr, TTY* = nullptr, Process* fork_parent = nullptr);
+    ErrorOr<NonnullLockRefPtr<Thread>> attach_resources(NonnullOwnPtr<Memory::AddressSpace>&&, Process* fork_parent);
     static ProcessID allocate_pid();
 
     void kill_threads_except_self();

Kernel/Scheduler.cpp

@@ -366,13 +366,11 @@ UNMAP_AFTER_INIT void Scheduler::initialize()
     VERIFY(Processor::is_initialized()); // sanity check
     VERIFY(TimeManagement::is_initialized());
 
-    LockRefPtr<Thread> idle_thread;
     g_finalizer_wait_queue = new WaitQueue;
 
     g_finalizer_has_work.store(false, AK::MemoryOrder::memory_order_release);
-    s_colonel_process = Process::create_kernel_process(idle_thread, KString::must_create("colonel"sv), idle_loop, nullptr, 1, Process::RegisterProcess::No).leak_ref();
-    VERIFY(s_colonel_process);
-    VERIFY(idle_thread);
+    auto [colonel_process, idle_thread] = MUST(Process::create_kernel_process(KString::must_create("colonel"sv), idle_loop, nullptr, 1, Process::RegisterProcess::No));
+    s_colonel_process = &colonel_process.leak_ref();
     idle_thread->set_priority(THREAD_PRIORITY_MIN);
     idle_thread->set_name(KString::must_create("Idle Task #0"sv));
 

Kernel/Syscalls/fork.cpp

@@ -18,19 +18,18 @@ ErrorOr<FlatPtr> Process::sys$fork(RegisterState& regs)
 {
     VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this);
     TRY(require_promise(Pledge::proc));
-    LockRefPtr<Thread> child_first_thread;
-
-    ArmedScopeGuard thread_finalizer_guard = [&child_first_thread]() {
-        SpinlockLocker lock(g_scheduler_lock);
-        if (child_first_thread) {
-            child_first_thread->detach();
-            child_first_thread->set_state(Thread::State::Dying);
-        }
-    };
 
     auto child_name = TRY(name().with([](auto& name) { return name->try_clone(); }));
     auto credentials = this->credentials();
-    auto child = TRY(Process::try_create(child_first_thread, move(child_name), credentials->uid(), credentials->gid(), pid(), m_is_kernel_process, current_directory(), executable(), m_tty, this));
+    auto child_and_first_thread = TRY(Process::create(move(child_name), credentials->uid(), credentials->gid(), pid(), m_is_kernel_process, current_directory(), executable(), m_tty, this));
+    auto& child = child_and_first_thread.process;
+    auto& child_first_thread = child_and_first_thread.first_thread;
+
+    ArmedScopeGuard thread_finalizer_guard = [&child_first_thread]() {
+        SpinlockLocker lock(g_scheduler_lock);
+        child_first_thread->detach();
+        child_first_thread->set_state(Thread::State::Dying);
+    };
 
     // NOTE: All user processes have a leaked ref on them. It's balanced by Thread::WaitBlockerSet::finalize().
     child->ref();

Kernel/Tasks/FinalizerTask.cpp

@@ -28,10 +28,8 @@ static void finalizer_task(void*)
 
 UNMAP_AFTER_INIT void FinalizerTask::spawn()
 {
-    LockRefPtr<Thread> finalizer_thread;
-    auto finalizer_process = Process::create_kernel_process(finalizer_thread, KString::must_create(finalizer_task_name), finalizer_task, nullptr);
-    VERIFY(finalizer_process);
-    g_finalizer = finalizer_thread;
+    auto [_, finalizer_thread] = MUST(Process::create_kernel_process(KString::must_create(finalizer_task_name), finalizer_task, nullptr));
+    g_finalizer = move(finalizer_thread);
 }
 
 }

Kernel/Tasks/SyncTask.cpp

@@ -14,14 +14,13 @@ namespace Kernel {
 
 UNMAP_AFTER_INIT void SyncTask::spawn()
 {
-    LockRefPtr<Thread> syncd_thread;
-    (void)Process::create_kernel_process(syncd_thread, KString::must_create("VFS Sync Task"sv), [] {
+    MUST(Process::create_kernel_process(KString::must_create("VFS Sync Task"sv), [] {
         dbgln("VFS SyncTask is running");
         for (;;) {
             VirtualFileSystem::sync();
             (void)Thread::current()->sleep(Time::from_seconds(1));
         }
-    });
+    }));
 }
 
 }

Kernel/WorkQueue.cpp

@@ -24,11 +24,10 @@ UNMAP_AFTER_INIT void WorkQueue::initialize()
 
 UNMAP_AFTER_INIT WorkQueue::WorkQueue(StringView name)
 {
-    LockRefPtr<Thread> thread;
     auto name_kstring = KString::try_create(name);
     if (name_kstring.is_error())
         TODO();
-    (void)Process::create_kernel_process(thread, name_kstring.release_value(), [this] {
+    auto [_, thread] = Process::create_kernel_process(name_kstring.release_value(), [this] {
 #if ARCH(AARCH64)
         // FIXME: This function expects to be executed with interrupts disabled, however on
         //        aarch64 we spawn (kernel) threads with interrupts enabled, so we need to disable them.
@@ -52,9 +51,8 @@ UNMAP_AFTER_INIT WorkQueue::WorkQueue(StringView name)
             }
             [[maybe_unused]] auto result = m_wait_queue.wait_on({});
         }
-    });
-    // If we can't create the thread we're in trouble...
-    m_thread = thread.release_nonnull();
+    }).release_value_but_fixme_should_propagate_errors();
+    m_thread = move(thread);
 }
 
 void WorkQueue::do_queue(WorkItem& item)