Kernel: Take some baby steps towards x86_64

Make more of the kernel compile in 64-bit mode, and make some things
pointer-size-agnostic (by using FlatPtr.)

There's a lot of work to do here before the kernel will even compile.

12 files changed, 187 insertions, 118 deletions

diff --git a/Kernel/API/Syscall.h b/Kernel/API/Syscall.h
index 7077deeaae..8333a41033 100644
--- a/Kernel/API/Syscall.h
+++ b/Kernel/API/Syscall.h
@@ -318,7 +318,7 @@ struct SC_futex_params {
     u32 val;
     union {
         const timespec* timeout;
-        u32 val2;
+        uintptr_t val2;
     };
     u32* userspace_address2;
     u32 val3;
diff --git a/Kernel/Arch/i386/CPU.cpp b/Kernel/Arch/i386/CPU.cpp
index f524d8b1f8..9d745fbae1 100644
--- a/Kernel/Arch/i386/CPU.cpp
+++ b/Kernel/Arch/i386/CPU.cpp
@@ -210,9 +210,7 @@ void page_fault_handler(TrapFrame* trap)
     clac();
 
     auto& regs = *trap->regs;
-    u32 fault_address;
-    asm("movl %%cr2, %%eax"
-        : "=a"(fault_address));
+    auto fault_address = read_cr2();
 
     if constexpr (PAGE_FAULT_DEBUG) {
         u32 fault_page_directory = read_cr3();
@@ -717,14 +715,22 @@ void exit_trap(TrapFrame* trap)
     return Processor::current().exit_trap(*trap);
 }
 
-UNMAP_AFTER_INIT void write_cr0(u32 value)
+UNMAP_AFTER_INIT void write_cr0(FlatPtr value)
 {
-    asm volatile("movl %%eax, %%cr0" ::"a"(value));
+#if ARCH(I386)
+    asm volatile("mov %%eax, %%cr0" ::"a"(value));
+#else
+    asm volatile("mov %%rax, %%cr0" ::"a"(value));
+#endif
 }
 
-UNMAP_AFTER_INIT void write_cr4(u32 value)
+UNMAP_AFTER_INIT void write_cr4(FlatPtr value)
 {
-    asm volatile("movl %%eax, %%cr4" ::"a"(value));
+#if ARCH(I386)
+    asm volatile("mov %%eax, %%cr4" ::"a"(value));
+#else
+    asm volatile("mov %%rax, %%cr4" ::"a"(value));
+#endif
 }
 
 UNMAP_AFTER_INIT static void sse_init()
@@ -733,50 +739,80 @@ UNMAP_AFTER_INIT static void sse_init()
     write_cr4(read_cr4() | 0x600);
 }
 
-u32 read_cr0()
+FlatPtr read_cr0()
 {
-    u32 cr0;
-    asm("movl %%cr0, %%eax"
+    FlatPtr cr0;
+#if ARCH(I386)
+    asm("mov %%cr0, %%eax"
         : "=a"(cr0));
+#else
+    asm("mov %%cr0, %%rax"
+        : "=a"(cr0));
+#endif
     return cr0;
 }
 
-u32 read_cr2()
+FlatPtr read_cr2()
 {
-    u32 cr2;
-    asm("movl %%cr2, %%eax"
+    FlatPtr cr2;
+#if ARCH(I386)
+    asm("mov %%cr2, %%eax"
         : "=a"(cr2));
+#else
+    asm("mov %%cr2, %%rax"
+        : "=a"(cr2));
+#endif
     return cr2;
 }
 
-u32 read_cr3()
+FlatPtr read_cr3()
 {
-    u32 cr3;
-    asm("movl %%cr3, %%eax"
+    FlatPtr cr3;
+#if ARCH(I386)
+    asm("mov %%cr3, %%eax"
         : "=a"(cr3));
+#else
+    asm("mov %%cr3, %%rax"
+        : "=a"(cr3));
+#endif
     return cr3;
 }
 
-void write_cr3(u32 cr3)
+void write_cr3(FlatPtr cr3)
 {
     // NOTE: If you're here from a GPF crash, it's very likely that a PDPT entry is incorrect, not this!
-    asm volatile("movl %%eax, %%cr3" ::"a"(cr3)
+#if ARCH(I386)
+    asm volatile("mov %%eax, %%cr3" ::"a"(cr3)
                  : "memory");
+#else
+    asm volatile("mov %%rax, %%cr3" ::"a"(cr3)
+                 : "memory");
+#endif
 }
 
-u32 read_cr4()
+FlatPtr read_cr4()
 {
-    u32 cr4;
-    asm("movl %%cr4, %%eax"
+    FlatPtr cr4;
+#if ARCH(I386)
+    asm("mov %%cr4, %%eax"
         : "=a"(cr4));
+#else
+    asm("mov %%cr4, %%rax"
+        : "=a"(cr4));
+#endif
     return cr4;
 }
 
-u32 read_dr6()
+FlatPtr read_dr6()
 {
-    u32 dr6;
-    asm("movl %%dr6, %%eax"
+    FlatPtr dr6;
+#if ARCH(I386)
+    asm("mov %%dr6, %%eax"
         : "=a"(dr6));
+#else
+    asm("mov %%dr6, %%rax"
+        : "=a"(dr6));
+#endif
     return dr6;
 }
 
@@ -1291,6 +1327,7 @@ void Processor::switch_context(Thread*& from_thread, Thread*& to_thread)
     dbgln_if(CONTEXT_SWITCH_DEBUG, "switch_context --> switching out of: {} {}", VirtualAddress(from_thread), *from_thread);
     from_thread->save_critical(m_in_critical);
 
+#if ARCH(I386)
     // clang-format off
     // Switch to new thread context, passing from_thread and to_thread
     // through to the new context using registers edx and eax
@@ -1333,6 +1370,9 @@ void Processor::switch_context(Thread*& from_thread, Thread*& to_thread)
         : "memory"
     );
     // clang-format on
+#else
+    PANIC("Context switching not implemented.");
+#endif
 
     dbgln_if(CONTEXT_SWITCH_DEBUG, "switch_context <-- from {} {} to {} {}", VirtualAddress(from_thread), *from_thread, VirtualAddress(to_thread), *to_thread);
 
@@ -1576,6 +1616,7 @@ UNMAP_AFTER_INIT void Processor::initialize_context_switching(Thread& initial_th
 
     m_scheduler_initialized = true;
 
+#if ARCH(I386)
     // clang-format off
     asm volatile(
         "movl %[new_esp], %%esp \n" // switch to new stack
@@ -1601,6 +1642,7 @@ UNMAP_AFTER_INIT void Processor::initialize_context_switching(Thread& initial_th
            [cpu] "c" (id())
     );
     // clang-format on
+#endif
 
     VERIFY_NOT_REACHED();
 }
diff --git a/Kernel/Arch/i386/CPU.h b/Kernel/Arch/i386/CPU.h
index c2f0a53976..d1bed13d9e 100644
--- a/Kernel/Arch/i386/CPU.h
+++ b/Kernel/Arch/i386/CPU.h
@@ -296,9 +296,9 @@ void load_task_register(u16 selector);
 #define sti() asm volatile("sti" :: \
                                : "memory")
 
-inline u32 cpu_flags()
+inline FlatPtr cpu_flags()
 {
-    u32 flags;
+    FlatPtr flags;
     asm volatile(
         "pushf\n"
         "pop %0\n"
@@ -441,29 +441,36 @@ private:
 };
 
 struct [[gnu::packed]] RegisterState {
-    u32 ss;
-    u32 gs;
-    u32 fs;
-    u32 es;
-    u32 ds;
-    u32 edi;
-    u32 esi;
-    u32 ebp;
-    u32 esp;
-    u32 ebx;
-    u32 edx;
-    u32 ecx;
-    u32 eax;
+    FlatPtr ss;
+    FlatPtr gs;
+    FlatPtr fs;
+    FlatPtr es;
+    FlatPtr ds;
+    FlatPtr edi;
+    FlatPtr esi;
+    FlatPtr ebp;
+    FlatPtr esp;
+    FlatPtr ebx;
+    FlatPtr edx;
+    FlatPtr ecx;
+    FlatPtr eax;
     u16 exception_code;
     u16 isr_number;
-    u32 eip;
-    u32 cs;
-    u32 eflags;
-    u32 userspace_esp;
-    u32 userspace_ss;
+#if ARCH(X86_64)
+    u32 padding;
+#endif
+    FlatPtr eip;
+    FlatPtr cs;
+    FlatPtr eflags;
+    FlatPtr userspace_esp;
+    FlatPtr userspace_ss;
 };
 
-#define REGISTER_STATE_SIZE (19 * 4)
+#if ARCH(I386)
+#    define REGISTER_STATE_SIZE (19 * 4)
+#else
+#    define REGISTER_STATE_SIZE (19 * 8)
+#endif
 static_assert(REGISTER_STATE_SIZE == sizeof(RegisterState));
 
 void copy_kernel_registers_into_ptrace_registers(PtraceRegisters&, const RegisterState&);
@@ -494,16 +501,16 @@ inline FlatPtr offset_in_page(const void* address)
     return offset_in_page((FlatPtr)address);
 }
 
-u32 read_cr0();
-u32 read_cr2();
-u32 read_cr3();
-u32 read_cr4();
+FlatPtr read_cr0();
+FlatPtr read_cr2();
+FlatPtr read_cr3();
+FlatPtr read_cr4();
 
-void write_cr0(u32);
-void write_cr3(u32);
-void write_cr4(u32);
+void write_cr0(FlatPtr);
+void write_cr3(FlatPtr);
+void write_cr4(FlatPtr);
 
-u32 read_dr6();
+FlatPtr read_dr6();
 
 static inline bool is_kernel_mode()
 {
@@ -1071,7 +1078,12 @@ struct TrapFrame {
     TrapFrame& operator=(TrapFrame&&) = delete;
 };
 
-#define TRAP_FRAME_SIZE (3 * sizeof(FlatPtr))
+#if ARCH(I386)
+#    define TRAP_FRAME_SIZE (3 * 4)
+#else
+#    define TRAP_FRAME_SIZE (3 * 8)
+#endif
+
 static_assert(TRAP_FRAME_SIZE == sizeof(TrapFrame));
 
 extern "C" void enter_trap_no_irq(TrapFrame*);
diff --git a/Kernel/Heap/SlabAllocator.cpp b/Kernel/Heap/SlabAllocator.cpp
index da5bc8d23b..7b12b3fa71 100644
--- a/Kernel/Heap/SlabAllocator.cpp
+++ b/Kernel/Heap/SlabAllocator.cpp
@@ -130,7 +130,9 @@ static SlabAllocator<32> s_slab_allocator_32;
 static SlabAllocator<64> s_slab_allocator_64;
 static SlabAllocator<128> s_slab_allocator_128;
 
+#if ARCH(I386)
 static_assert(sizeof(Region) <= s_slab_allocator_128.slab_size());
+#endif
 
 template<typename Callback>
 void for_each_allocator(Callback callback)
diff --git a/Kernel/KSyms.cpp b/Kernel/KSyms.cpp
index 27208c5a0b..dc77c21550 100644
--- a/Kernel/KSyms.cpp
+++ b/Kernel/KSyms.cpp
@@ -48,7 +48,7 @@ static u8 parse_hex_digit(char nibble)
     return 10 + (nibble - 'a');
 }
 
-u32 address_for_kernel_symbol(const StringView& name)
+FlatPtr address_for_kernel_symbol(const StringView& name)
 {
     for (size_t i = 0; i < s_symbol_count; ++i) {
         if (!strncmp(name.characters_without_null_termination(), s_symbols[i].name, name.length()))
@@ -57,7 +57,7 @@ u32 address_for_kernel_symbol(const StringView& name)
     return 0;
 }
 
-const KernelSymbol* symbolicate_kernel_address(u32 address)
+const KernelSymbol* symbolicate_kernel_address(FlatPtr address)
 {
     if (address < g_lowest_kernel_symbol_address || address > g_highest_kernel_symbol_address)
         return nullptr;
@@ -147,7 +147,7 @@ NEVER_INLINE static void dump_backtrace_impl(FlatPtr base_pointer, bool use_ksym
         FlatPtr* stack_ptr = (FlatPtr*)base_pointer;
         while (stack_ptr && safe_memcpy(copied_stack_ptr, stack_ptr, sizeof(copied_stack_ptr), fault_at)) {
             FlatPtr retaddr = copied_stack_ptr[1];
-            dbgln("{:p} (next: {:p})", retaddr, stack_ptr ? (u32*)copied_stack_ptr[0] : 0);
+            dbgln("{:p} (next: {:p})", retaddr, stack_ptr ? (FlatPtr*)copied_stack_ptr[0] : 0);
             stack_ptr = (FlatPtr*)copied_stack_ptr[0];
         }
         return;
diff --git a/Kernel/KSyms.h b/Kernel/KSyms.h
index 102ae06c18..a872ddf8bd 100644
--- a/Kernel/KSyms.h
+++ b/Kernel/KSyms.h
@@ -31,12 +31,12 @@
 namespace Kernel {
 
 struct KernelSymbol {
-    u32 address;
+    FlatPtr address;
     const char* name;
 };
 
-u32 address_for_kernel_symbol(const StringView& name);
-const KernelSymbol* symbolicate_kernel_address(u32 address);
+FlatPtr address_for_kernel_symbol(const StringView& name);
+const KernelSymbol* symbolicate_kernel_address(FlatPtr);
 void load_kernel_symbol_table();
 
 extern bool g_kernel_symbols_available;
diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index d518106c37..e4ed6f2f31 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -260,6 +260,7 @@ Process::~Process()
 extern void signal_trampoline_dummy();
 void signal_trampoline_dummy()
 {
+#if ARCH(I386)
     // The trampoline preserves the current eax, pushes the signal code and
     // then calls the signal handler. We do this because, when interrupting a
     // blocking syscall, that syscall may return some special error code in eax;
@@ -280,6 +281,9 @@ void signal_trampoline_dummy()
         "int 0x82\n" // sigreturn syscall
         "asm_signal_trampoline_end:\n"
         ".att_syntax" ::"i"(Syscall::SC_sigreturn));
+#else
+    // FIXME: Implement trampoline for other architectures.
+#endif
 }
 
 extern "C" void asm_signal_trampoline(void);
diff --git a/Kernel/Process.h b/Kernel/Process.h
index e4ba7c7b77..ee9838e36a 100644
--- a/Kernel/Process.h
+++ b/Kernel/Process.h
@@ -251,8 +251,8 @@ public:
     [[noreturn]] void sys$exit(int status);
     int sys$sigreturn(RegisterState& registers);
     pid_t sys$waitid(Userspace<const Syscall::SC_waitid_params*>);
-    void* sys$mmap(Userspace<const Syscall::SC_mmap_params*>);
-    void* sys$mremap(Userspace<const Syscall::SC_mremap_params*>);
+    FlatPtr sys$mmap(Userspace<const Syscall::SC_mmap_params*>);
+    FlatPtr sys$mremap(Userspace<const Syscall::SC_mremap_params*>);
     int sys$munmap(void*, size_t size);
     int sys$set_mmap_name(Userspace<const Syscall::SC_set_mmap_name_params*>);
     int sys$mprotect(void*, size_t, int prot);
@@ -352,7 +352,7 @@ public:
     int sys$recvfd(int sockfd, int options);
     long sys$sysconf(int name);
     int sys$disown(ProcessID);
-    void* sys$allocate_tls(size_t);
+    FlatPtr sys$allocate_tls(size_t);
     int sys$prctl(int option, FlatPtr arg1, FlatPtr arg2);
     int sys$set_coredump_metadata(Userspace<const Syscall::SC_set_coredump_metadata_params*>);
     void sys$abort();
diff --git a/Kernel/Syscalls/mmap.cpp b/Kernel/Syscalls/mmap.cpp
index 8b0536e00f..e194e45c23 100644
--- a/Kernel/Syscalls/mmap.cpp
+++ b/Kernel/Syscalls/mmap.cpp
@@ -137,13 +137,13 @@ static bool validate_inode_mmap_prot(const Process& process, int prot, const Ino
     return true;
 }
 
-void* Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> user_params)
+FlatPtr Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> user_params)
 {
     REQUIRE_PROMISE(stdio);
 
     Syscall::SC_mmap_params params;
     if (!copy_from_user(&params, user_params))
-        return (void*)-EFAULT;
+        return -EFAULT;
 
     void* addr = (void*)params.addr;
     size_t size = params.size;
@@ -162,27 +162,27 @@ void* Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> user_params)
     }
 
     if (alignment & ~PAGE_MASK)
-        return (void*)-EINVAL;
+        return -EINVAL;
 
     if (page_round_up_would_wrap(size))
-        return (void*)-EINVAL;
+        return -EINVAL;
 
     if (!is_user_range(VirtualAddress(addr), page_round_up(size)))
-        return (void*)-EFAULT;
+        return -EFAULT;
 
     String name;
     if (params.name.characters) {
         if (params.name.length > PATH_MAX)
-            return (void*)-ENAMETOOLONG;
+            return -ENAMETOOLONG;
         name = copy_string_from_user(params.name);
         if (name.is_null())
-            return (void*)-EFAULT;
+            return -EFAULT;
     }
 
     if (size == 0)
-        return (void*)-EINVAL;
+        return -EINVAL;
     if ((FlatPtr)addr & ~PAGE_MASK)
-        return (void*)-EINVAL;
+        return -EINVAL;
 
     bool map_shared = flags & MAP_SHARED;
     bool map_anonymous = flags & MAP_ANONYMOUS;
@@ -193,19 +193,19 @@ void* Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> user_params)
     bool map_randomized = flags & MAP_RANDOMIZED;
 
     if (map_shared && map_private)
-        return (void*)-EINVAL;
+        return -EINVAL;
 
     if (!map_shared && !map_private)
-        return (void*)-EINVAL;
+        return -EINVAL;
 
     if (map_fixed && map_randomized)
-        return (void*)-EINVAL;
+        return -EINVAL;
 
     if (!validate_mmap_prot(prot, map_stack, map_anonymous))
-        return (void*)-EINVAL;
+        return -EINVAL;
 
     if (map_stack && (!map_private || !map_anonymous))
-        return (void*)-EINVAL;
+        return -EINVAL;
 
     Region* region = nullptr;
     Optional<Range> range;
@@ -223,44 +223,44 @@ void* Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> user_params)
     }
 
     if (!range.has_value())
-        return (void*)-ENOMEM;
+        return -ENOMEM;
 
     if (map_anonymous) {
         auto strategy = map_noreserve ? AllocationStrategy::None : AllocationStrategy::Reserve;
         auto region_or_error = space().allocate_region(range.value(), !name.is_null() ? name : "mmap", prot, strategy);
         if (region_or_error.is_error())
-            return (void*)region_or_error.error().error();
+            return region_or_error.error().error();
         region = region_or_error.value();
     } else {
         if (offset < 0)
-            return (void*)-EINVAL;
+            return -EINVAL;
         if (static_cast<size_t>(offset) & ~PAGE_MASK)
-            return (void*)-EINVAL;
+            return -EINVAL;
         auto description = file_description(fd);
         if (!description)
-            return (void*)-EBADF;
+            return -EBADF;
         if (description->is_directory())
-            return (void*)-ENODEV;
+            return -ENODEV;
         // Require read access even when read protection is not requested.
         if (!description->is_readable())
-            return (void*)-EACCES;
+            return -EACCES;
         if (map_shared) {
             if ((prot & PROT_WRITE) && !description->is_writable())
-                return (void*)-EACCES;
+                return -EACCES;
         }
         if (description->inode()) {
             if (!validate_inode_mmap_prot(*this, prot, *description->inode(), map_shared))
-                return (void*)-EACCES;
+                return -EACCES;
         }
 
         auto region_or_error = description->mmap(*this, range.value(), static_cast<size_t>(offset), prot, map_shared);
         if (region_or_error.is_error())
-            return (void*)region_or_error.error().error();
+            return region_or_error.error().error();
         region = region_or_error.value();
     }
 
     if (!region)
-        return (void*)-ENOMEM;
+        return -ENOMEM;
     region->set_mmap(true);
     if (map_shared)
         region->set_shared(true);
@@ -268,7 +268,7 @@ void* Process::sys$mmap(Userspace<const Syscall::SC_mmap_params*> user_params)
         region->set_stack(true);
     if (!name.is_null())
         region->set_name(name);
-    return region->vaddr().as_ptr();
+    return region->vaddr().get();
 }
 
 static KResultOr<Range> expand_range_to_page_boundaries(FlatPtr address, size_t size)
@@ -494,26 +494,26 @@ int Process::sys$munmap(void* addr, size_t size)
     return -EINVAL;
 }
 
-void* Process::sys$mremap(Userspace<const Syscall::SC_mremap_params*> user_params)
+FlatPtr Process::sys$mremap(Userspace<const Syscall::SC_mremap_params*> user_params)
 {
     REQUIRE_PROMISE(stdio);
 
     Syscall::SC_mremap_params params {};
     if (!copy_from_user(&params, user_params))
-        return (void*)-EFAULT;
+        return -EFAULT;
 
     auto range_or_error = expand_range_to_page_boundaries((FlatPtr)params.old_address, params.old_size);
     if (range_or_error.is_error())
-        return (void*)range_or_error.error().error();
+        return range_or_error.error().error();
 
     auto old_range = range_or_error.value();
 
     auto* old_region = space().find_region_from_range(old_range);
     if (!old_region)
-        return (void*)-EINVAL;
+        return -EINVAL;
 
     if (!old_region->is_mmap())
-        return (void*)-EPERM;
+        return -EPERM;
 
     if (old_region->vmobject().is_shared_inode() && params.flags & MAP_PRIVATE && !(params.flags & (MAP_ANONYMOUS | MAP_NORESERVE))) {
         auto range = old_region->range();
@@ -529,28 +529,28 @@ void* Process::sys$mremap(Userspace<const Syscall::SC_mremap_params*> user_param
 
         auto new_region_or_error = space().allocate_region_with_vmobject(range, new_vmobject, 0, old_name, old_prot, false);
         if (new_region_or_error.is_error())
-            return (void*)new_region_or_error.error().error();
+            return new_region_or_error.error().error();
         auto& new_region = *new_region_or_error.value();
         new_region.set_mmap(true);
-        return new_region.vaddr().as_ptr();
+        return new_region.vaddr().get();
     }
 
     dbgln("sys$mremap: Unimplemented remap request (flags={})", params.flags);
-    return (void*)-ENOTIMPL;
+    return -ENOTIMPL;
 }
 
-void* Process::sys$allocate_tls(size_t size)
+FlatPtr Process::sys$allocate_tls(size_t size)
 {
     REQUIRE_PROMISE(stdio);
 
     if (!size)
-        return (void*)-EINVAL;
+        return -EINVAL;
 
     if (!m_master_tls_region.is_null())
-        return (void*)-EEXIST;
+        return -EEXIST;
 
     if (thread_count() != 1)
-        return (void*)-EFAULT;
+        return -EFAULT;
 
     Thread* main_thread = nullptr;
     for_each_thread([&main_thread](auto& thread) {
@@ -561,11 +561,11 @@ void* Process::sys$allocate_tls(size_t size)
 
     auto range = space().allocate_range({}, size);
     if (!range.has_value())
-        return (void*)-ENOMEM;
+        return -ENOMEM;
 
     auto region_or_error = space().allocate_region(range.value(), String(), PROT_READ | PROT_WRITE);
     if (region_or_error.is_error())
-        return (void*)region_or_error.error().error();
+        return region_or_error.error().error();
 
     m_master_tls_region = region_or_error.value()->make_weak_ptr();
     m_master_tls_size = size;
@@ -573,13 +573,13 @@ void* Process::sys$allocate_tls(size_t size)
 
     auto tsr_result = main_thread->make_thread_specific_region({});
     if (tsr_result.is_error())
-        return (void*)-EFAULT;
+        return -EFAULT;
 
     auto& tls_descriptor = Processor::current().get_gdt_entry(GDT_SELECTOR_TLS);
     tls_descriptor.set_base(main_thread->thread_specific_data());
     tls_descriptor.set_limit(main_thread->thread_specific_region_size());
 
-    return m_master_tls_region.unsafe_ptr()->vaddr().as_ptr();
+    return m_master_tls_region.unsafe_ptr()->vaddr().get();
 }
 
 int Process::sys$msyscall(void* address)
diff --git a/Kernel/Syscalls/module.cpp b/Kernel/Syscalls/module.cpp
index 6582d3782d..eae1897d07 100644
--- a/Kernel/Syscalls/module.cpp
+++ b/Kernel/Syscalls/module.cpp
@@ -87,11 +87,11 @@ int Process::sys$module_load(Userspace<const char*> user_path, size_t path_lengt
             case R_386_PC32: {
                 // PC-relative relocation
                 dbgln("PC-relative relocation: {}", relocation.symbol().name());
-                u32 symbol_address = address_for_kernel_symbol(relocation.symbol().name());
+                auto symbol_address = address_for_kernel_symbol(relocation.symbol().name());
                 if (symbol_address == 0)
                     missing_symbols = true;
                 dbgln("   Symbol address: {:p}", symbol_address);
-                ptrdiff_t relative_offset = (char*)symbol_address - ((char*)&patch_ptr + 4);
+                ptrdiff_t relative_offset = (FlatPtr)symbol_address - ((FlatPtr)&patch_ptr + 4);
                 patch_ptr = relative_offset;
                 break;
             }
diff --git a/Kernel/Syscalls/thread.cpp b/Kernel/Syscalls/thread.cpp
index 34d285f417..90b242ce0c 100644
--- a/Kernel/Syscalls/thread.cpp
+++ b/Kernel/Syscalls/thread.cpp
@@ -83,7 +83,7 @@ int Process::sys$create_thread(void* (*entry)(void*), Userspace<const Syscall::S
     tss.eip = (FlatPtr)entry;
     tss.eflags = 0x0202;
     tss.cr3 = space().page_directory().cr3();
-    tss.esp = (u32)user_stack_address;
+    tss.esp = (FlatPtr)user_stack_address;
 
     auto tsr_result = thread->make_thread_specific_region({});
     if (tsr_result.is_error())
diff --git a/Kernel/Thread.cpp b/Kernel/Thread.cpp
index 38d359180a..51a6a632aa 100644
--- a/Kernel/Thread.cpp
+++ b/Kernel/Thread.cpp
@@ -666,10 +666,10 @@ bool Thread::has_signal_handler(u8 signal) const
     return !action.handler_or_sigaction.is_null();
 }
 
-static bool push_value_on_user_stack(u32* stack, u32 data)
+static bool push_value_on_user_stack(FlatPtr* stack, FlatPtr data)
 {
-    *stack -= 4;
-    return copy_to_user((u32*)*stack, &data);
+    *stack -= sizeof(FlatPtr);
+    return copy_to_user((FlatPtr*)*stack, &data);
 }
 
 void Thread::resume_from_stopped()
@@ -792,19 +792,24 @@ DispatchSignalResult Thread::dispatch_signal(u8 signal)
     m_have_any_unmasked_pending_signals.store(m_pending_signals & ~m_signal_mask, AK::memory_order_release);
 
     auto setup_stack = [&](RegisterState& state) {
-        u32* stack = &state.userspace_esp;
-        u32 old_esp = *stack;
-        u32 ret_eip = state.eip;
-        u32 ret_eflags = state.eflags;
+#if ARCH(I386)
+        FlatPtr* stack = &state.userspace_esp;
+#elif ARCH(X86_64)
+        FlatPtr* stack = &state.userspace_esp;
+#endif
+        FlatPtr old_esp = *stack;
+        FlatPtr ret_eip = state.eip;
+        FlatPtr ret_eflags = state.eflags;
 
 #if SIGNAL_DEBUG
         klog() << "signal: setting up user stack to return to eip: " << String::format("%p", (void*)ret_eip) << " esp: " << String::format("%p", (void*)old_esp);
 #endif
 
+#if ARCH(I386)
         // Align the stack to 16 bytes.
         // Note that we push 56 bytes (4 * 14) on to the stack,
         // so we need to account for this here.
-        u32 stack_alignment = (*stack - 56) % 16;
+        FlatPtr stack_alignment = (*stack - 56) % 16;
         *stack -= stack_alignment;
 
         push_value_on_user_stack(stack, ret_eflags);
@@ -819,6 +824,10 @@ DispatchSignalResult Thread::dispatch_signal(u8 signal)
         push_value_on_user_stack(stack, state.esi);
         push_value_on_user_stack(stack, state.edi);
 
+#elif ARCH(X86_64)
+        // FIXME
+#endif
+
         // PUSH old_signal_mask
         push_value_on_user_stack(stack, old_signal_mask);
 
@@ -941,7 +950,7 @@ void Thread::set_state(State new_state, u8 stop_signal)
 }
 
 struct RecognizedSymbol {
-    u32 address;
+    FlatPtr address;
     const KernelSymbol* symbol { nullptr };
 };