Kernel: Support 64-bit addresses for kernel thread stacks

Author: https://github.com/gunnarbeutner
Commit: https://github.com/SerenityOS/serenity/commit/6c6b778e2e2
Pull-request: https://github.com/SerenityOS/serenity/pull/8795
Reviewed-by: https://github.com/Hendiadyoin1

Kernel/Thread.cpp

@@ -122,7 +122,7 @@ Thread::Thread(NonnullRefPtr<Process> process, NonnullOwnPtr<Region> kernel_stac
     m_regs.cr3 = m_process->space().page_directory().cr3();
 
     m_kernel_stack_base = m_kernel_stack_region->vaddr().get();
-    m_kernel_stack_top = m_kernel_stack_region->vaddr().offset(default_kernel_stack_size).get() & 0xfffffff8u;
+    m_kernel_stack_top = m_kernel_stack_region->vaddr().offset(default_kernel_stack_size).get() & ~(FlatPtr)0x7u;
 
     if (m_process->is_kernel_process()) {
 #if ARCH(I386)

Kernel/Thread.h

@@ -991,8 +991,8 @@ public:
     void set_ticks_left(u32 t) { m_ticks_left = t; }
     u32 ticks_left() const { return m_ticks_left; }
 
-    u32 kernel_stack_base() const { return m_kernel_stack_base; }
-    u32 kernel_stack_top() const { return m_kernel_stack_top; }
+    FlatPtr kernel_stack_base() const { return m_kernel_stack_base; }
+    FlatPtr kernel_stack_top() const { return m_kernel_stack_top; }
 
     void set_state(State, u8 = 0);
 
@@ -1276,8 +1276,8 @@ private:
     u32 m_ticks_in_kernel { 0 };
     u32 m_pending_signals { 0 };
     u32 m_signal_mask { 0 };
-    u32 m_kernel_stack_base { 0 };
-    u32 m_kernel_stack_top { 0 };
+    FlatPtr m_kernel_stack_base { 0 };
+    FlatPtr m_kernel_stack_top { 0 };
     OwnPtr<Region> m_kernel_stack_region;
     VirtualAddress m_thread_specific_data;
     Optional<Range> m_thread_specific_range;