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/common/ProcessorInfo.cpp

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/StringBuilder.h>
+#include <AK/Types.h>
+#include <Kernel/Arch/x86/CPUID.h>
+#include <Kernel/Arch/x86/Processor.h>
+#include <Kernel/Arch/x86/ProcessorInfo.h>
+
+namespace Kernel {
+
+ProcessorInfo::ProcessorInfo(Processor& processor)
+    : m_processor(processor)
+{
+    u32 max_leaf;
+    {
+        CPUID cpuid(0);
+        StringBuilder builder;
+        auto emit_u32 = [&](u32 value) {
+            builder.appendff("{:c}{:c}{:c}{:c}",
+                value & 0xff,
+                (value >> 8) & 0xff,
+                (value >> 16) & 0xff,
+                (value >> 24) & 0xff);
+        };
+        max_leaf = cpuid.eax();
+        emit_u32(cpuid.ebx());
+        emit_u32(cpuid.edx());
+        emit_u32(cpuid.ecx());
+        m_cpuid = builder.build();
+    }
+    {
+        VERIFY(max_leaf >= 1);
+        CPUID cpuid(1);
+        m_stepping = cpuid.eax() & 0xf;
+        u32 model = (cpuid.eax() >> 4) & 0xf;
+        u32 family = (cpuid.eax() >> 8) & 0xf;
+        m_type = (cpuid.eax() >> 12) & 0x3;
+        u32 extended_model = (cpuid.eax() >> 16) & 0xf;
+        u32 extended_family = (cpuid.eax() >> 20) & 0xff;
+        if (family == 15) {
+            m_display_family = family + extended_family;
+            m_display_model = model + (extended_model << 4);
+        } else if (family == 6) {
+            m_display_family = family;
+            m_display_model = model + (extended_model << 4);
+        } else {
+            m_display_family = family;
+            m_display_model = model;
+        }
+    }
+
+    u32 max_extended_leaf = CPUID(0x80000000).eax();
+
+    if (max_extended_leaf >= 0x80000004) {
+        alignas(u32) char buffer[48];
+        u32* bufptr = reinterpret_cast<u32*>(buffer);
+        auto copy_brand_string_part_to_buffer = [&](u32 i) {
+            CPUID cpuid(0x80000002 + i);
+            *bufptr++ = cpuid.eax();
+            *bufptr++ = cpuid.ebx();
+            *bufptr++ = cpuid.ecx();
+            *bufptr++ = cpuid.edx();
+        };
+        copy_brand_string_part_to_buffer(0);
+        copy_brand_string_part_to_buffer(1);
+        copy_brand_string_part_to_buffer(2);
+        m_brandstr = buffer;
+    }
+
+    // Cache the CPU feature string
+    m_features = m_processor.features_string();
+}
+
+}