Kernel: Add stubs for missing x86_64 functionality

This adds just enough stubs to make the kernel compile on x86_64. Obviously
it won't do anything useful - in fact it won't even attempt to boot because
Multiboot doesn't support ELF64 binaries - but it gets those compiler errors
out of the way so more progress can be made getting all the missing
functionality in place.

Kernel/Arch/x86/x86_64/Boot/boot.S

@@ -317,7 +317,8 @@ apic_ap_start32:
     movl $0x80000001, %eax
     cpuid
     testl $0x100000, %edx
-    je (1f - apic_ap_start + 0x8000)
+    // TODO: Uncomment this
+    //je (1f - apic_ap_start + 0x8000)
     /* turn on IA32_EFER.NXE */
     movl $0xc0000080, %ecx
     rdmsr

Kernel/Arch/x86/x86_64/CPU.cpp

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Assertions.h>
+#include <AK/Types.h>
+
+#include <Kernel/Arch/x86/CPU.h>
+#include <Kernel/Arch/x86/Processor.h>
+#include <Kernel/Arch/x86/TrapFrame.h>
+#include <Kernel/KSyms.h>
+#include <Kernel/Process.h>
+#include <Kernel/Thread.h>
+
+namespace Kernel {
+
+// The compiler can't see the calls to these functions inside assembly.
+// Declare them, to avoid dead code warnings.
+extern "C" void enter_thread_context(Thread* from_thread, Thread* to_thread) __attribute__((used));
+extern "C" void context_first_init(Thread* from_thread, Thread* to_thread, TrapFrame* trap) __attribute__((used));
+extern "C" u32 do_init_context(Thread* thread, u32 flags) __attribute__((used));
+
+extern "C" void enter_thread_context(Thread* from_thread, Thread* to_thread)
+{
+    (void)from_thread;
+    (void)to_thread;
+    TODO();
+}
+
+extern "C" void context_first_init([[maybe_unused]] Thread* from_thread, [[maybe_unused]] Thread* to_thread, [[maybe_unused]] TrapFrame* trap)
+{
+    TODO();
+}
+
+extern "C" u32 do_init_context(Thread* thread, u32 flags)
+{
+    (void)thread;
+    (void)flags;
+    TODO();
+}
+}

Kernel/Arch/x86/x86_64/InterruptEntry.cpp

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Gunnar Beutner <gbeutner@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Arch/x86/DescriptorTable.h>
+#include <Kernel/Arch/x86/TrapFrame.h>
+
+// clang-format off
+asm(
+".globl interrupt_common_asm_entry\n"
+"interrupt_common_asm_entry: \n"
+"    int3 \n" // FIXME
+".globl common_trap_exit \n"
+"common_trap_exit: \n"
+// another thread may have handled this trap at this point, so don't
+// make assumptions about the stack other than there's a TrapFrame
+// and a pointer to it.
+"    call exit_trap \n"
+"    int3 \n" // FIXME
+);
+// clang-format on

Kernel/Arch/x86/x86_64/Processor.cpp

@@ -88,6 +88,7 @@ u32 Processor::init_context(Thread& thread, bool leave_crit)
     // TODO: handle NT?
     VERIFY((cpu_flags() & 0x24000) == 0); // Assume !(NT | VM)
 
+#if 0
     auto& tss = thread.tss();
     bool return_to_user = (tss.cs & 3) != 0;
 
@@ -116,7 +117,6 @@ u32 Processor::init_context(Thread& thread, bool leave_crit)
     // However, the first step is to always start in kernel mode with thread_context_first_enter
     RegisterState& iretframe = *reinterpret_cast<RegisterState*>(stack_top);
     // FIXME: copy state to be recovered through TSS
-    TODO();
 
     // make space for a trap frame
     stack_top -= sizeof(TrapFrame);
@@ -161,6 +161,9 @@ u32 Processor::init_context(Thread& thread, bool leave_crit)
     tss.gs = GDT_SELECTOR_DATA0;
     tss.ss = GDT_SELECTOR_DATA0;
     tss.fs = GDT_SELECTOR_PROC;
+#else
+    TODO();
+#endif
     return stack_top;
 }
 
@@ -202,11 +205,15 @@ UNMAP_AFTER_INIT void Processor::initialize_context_switching(Thread& initial_th
 
     auto& tss = initial_thread.tss();
     m_tss = tss;
+#if 0
     m_tss.esp0 = tss.esp0;
     m_tss.ss0 = GDT_SELECTOR_DATA0;
     // user mode needs to be able to switch to kernel mode:
     m_tss.cs = m_tss.ds = m_tss.es = m_tss.gs = m_tss.ss = GDT_SELECTOR_CODE0 | 3;
     m_tss.fs = GDT_SELECTOR_PROC | 3;
+#else
+    TODO();
+#endif
 
     m_scheduler_initialized = true;
 

Kernel/Arch/x86/x86_64/SafeMem.cpp

@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2021, Gunnar Beutner <gbeutner@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Arch/x86/SafeMem.h>
+
+#define CODE_SECTION(section_name) __attribute__((section(section_name)))
+
+namespace Kernel {
+
+CODE_SECTION(".text.safemem")
+NEVER_INLINE bool safe_memcpy(void* dest_ptr, const void* src_ptr, size_t n, void*& fault_at)
+{
+    (void)dest_ptr;
+    (void)src_ptr;
+    (void)n;
+    (void)fault_at;
+    TODO();
+}
+
+CODE_SECTION(".text.safemem")
+NEVER_INLINE ssize_t safe_strnlen(const char* str, size_t max_n, void*& fault_at)
+{
+    (void)str;
+    (void)max_n;
+    (void)fault_at;
+    TODO();
+}
+
+CODE_SECTION(".text.safemem")
+NEVER_INLINE bool safe_memset(void* dest_ptr, int c, size_t n, void*& fault_at)
+{
+    (void)dest_ptr;
+    (void)c;
+    (void)n;
+    (void)fault_at;
+    TODO();
+}
+
+CODE_SECTION(".text.safemem.atomic")
+NEVER_INLINE Optional<u32> safe_atomic_fetch_add_relaxed(volatile u32* var, u32 val)
+{
+    (void)var;
+    (void)val;
+    TODO();
+}
+
+CODE_SECTION(".text.safemem.atomic")
+NEVER_INLINE Optional<u32> safe_atomic_exchange_relaxed(volatile u32* var, u32 val)
+{
+    (void)var;
+    (void)val;
+    TODO();
+}
+
+CODE_SECTION(".text.safemem.atomic")
+NEVER_INLINE Optional<u32> safe_atomic_load_relaxed(volatile u32* var)
+{
+    (void)var;
+    TODO();
+}
+
+CODE_SECTION(".text.safemem.atomic")
+NEVER_INLINE bool safe_atomic_store_relaxed(volatile u32* var, u32 val)
+{
+    (void)var;
+    (void)val;
+    TODO();
+}
+
+CODE_SECTION(".text.safemem.atomic")
+NEVER_INLINE Optional<bool> safe_atomic_compare_exchange_relaxed(volatile u32* var, u32& expected, u32 val)
+{
+    (void)var;
+    (void)expected;
+    (void)val;
+    TODO();
+}
+
+bool handle_safe_access_fault(RegisterState& regs, u32 fault_address)
+{
+    (void)regs;
+    (void)fault_address;
+    TODO();
+}
+
+}