Kernel: Move ThreadRegisters into arch-specific directory

These are architecture-specific anyway, so they belong in the Arch
directory. This commit also adds ThreadRegisters::set_initial_state to
factor out the logic in Thread.cpp.

Kernel/Arch/ThreadRegisters.h

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2022, Timon Kruiper <timonkruiper@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Platform.h>
+
+#if ARCH(X86_64)
+#    include <Kernel/Arch/x86_64/ThreadRegisters.h>
+#elif ARCH(AARCH64)
+#    include <Kernel/Arch/aarch64/ThreadRegisters.h>
+#else
+#    error "Unknown architecture"
+#endif

Kernel/Arch/aarch64/ThreadRegisters.h

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2022, Timon Kruiper <timonkruiper@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+#include <Kernel/Memory/AddressSpace.h>
+
+namespace Kernel {
+
+struct ThreadRegisters {
+    u64 x[31];
+    u64 elr_el1;
+    u64 sp_el0;
+
+    FlatPtr ip() const { return elr_el1; }
+    void set_ip(FlatPtr value) { elr_el1 = value; }
+
+    void set_sp(FlatPtr value) { sp_el0 = value; }
+
+    void set_initial_state(bool, Memory::AddressSpace&, FlatPtr kernel_stack_top)
+    {
+        set_sp(kernel_stack_top);
+    }
+};
+
+}

Kernel/Arch/x86_64/ThreadRegisters.h

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2021, Gunnar Beutner <gbeutner@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Platform.h>
+#include <AK/Types.h>
+#include <Kernel/Memory/AddressSpace.h>
+
+namespace Kernel {
+
+struct ThreadRegisters {
+    FlatPtr rdi;
+    FlatPtr rsi;
+    FlatPtr rbp;
+    FlatPtr rsp;
+    FlatPtr rbx;
+    FlatPtr rdx;
+    FlatPtr rcx;
+    FlatPtr rax;
+    FlatPtr r8;
+    FlatPtr r9;
+    FlatPtr r10;
+    FlatPtr r11;
+    FlatPtr r12;
+    FlatPtr r13;
+    FlatPtr r14;
+    FlatPtr r15;
+    FlatPtr rip;
+    FlatPtr rsp0;
+    FlatPtr cs;
+
+    FlatPtr rflags;
+    FlatPtr flags() const { return rflags; }
+    void set_flags(FlatPtr value) { rflags = value; }
+    void set_sp(FlatPtr value) { rsp = value; }
+    void set_sp0(FlatPtr value) { rsp0 = value; }
+    void set_ip(FlatPtr value) { rip = value; }
+
+    FlatPtr cr3;
+
+    FlatPtr ip() const
+    {
+        return rip;
+    }
+
+    FlatPtr sp() const
+    {
+        return rsp;
+    }
+
+    void set_initial_state(bool is_kernel_process, Memory::AddressSpace& space, FlatPtr kernel_stack_top)
+    {
+        // Only IF is set when a process boots.
+        set_flags(0x0202);
+
+        if (is_kernel_process)
+            cs = GDT_SELECTOR_CODE0;
+        else
+            cs = GDT_SELECTOR_CODE3 | 3;
+
+        cr3 = space.page_directory().cr3();
+
+        if (is_kernel_process) {
+            set_sp(kernel_stack_top);
+            set_sp0(kernel_stack_top);
+        } else {
+            // Ring 3 processes get a separate stack for ring 0.
+            // The ring 3 stack will be assigned by exec().
+            set_sp0(kernel_stack_top);
+        }
+    }
+};
+
+}