Add a bootstrap physical memory manager.

This will allow the real physical memory manager to use allocations.

.gdbinit

@@ -0,0 +1,3 @@
+target remote localhost:1234
+file builddbg/zion/zion
+break zion

CMakeLists.txt

@@ -19,6 +19,11 @@ add_custom_command(
 )
 
 add_custom_target(qemu
-  COMMAND qemu-system-x86_64 -d guest_errors -m 1G -serial stdio -hda disk.img --boot c
+  COMMAND qemu-system-x86_64 -d guest_errors -m 1G -serial stdio -hda disk.img
+  DEPENDS disk.img
+  USES_TERMINAL)
+
+add_custom_target(qemu-dbg
+  COMMAND qemu-system-x86_64 -d guest_errors -m 1G -serial stdio -hda disk.img -S -s
   DEPENDS disk.img
   USES_TERMINAL)

init-dbg.sh

@@ -1,2 +1,2 @@
 #! /bin/bash
-cmake -B builddbg/ -G Ninja -D CMAKE_CXX_COMPILER=x86_64-elf-gcc -D CMAKE_ASM-ATT_COMPILER=x86_64-elf-as -D CMAKE_BUILD_TYPE=Debug 
+cmake -B builddbg/ -G Ninja -D CMAKE_CXX_COMPILER=x86_64-elf-gcc -D CMAKE_ASM-ATT_COMPILER=x86_64-elf-gcc -D CMAKE_BUILD_TYPE=Debug 

zion/CMakeLists.txt

@@ -1,5 +1,13 @@
 add_executable(zion
+  boot/boot_info.cpp
+  common/gdt.cpp
+  common/load_gdt.s
   debug/debug.cpp
+  interrupt/interrupt.cpp
+  interrupt/interrupt_enter.s
+  memory/kernel_heap.cpp
+  memory/paging_util.cpp
+  memory/physical_memory.cpp
   zion.cpp)
 
 target_include_directories(zion
@@ -7,20 +15,14 @@ target_include_directories(zion
   ${CMAKE_CURRENT_SOURCE_DIR}
   )
 
-# -c -- Don't run the linker.
+# -c -- Don't run the linker (only necessary for the assembler)
+# -ffreestanding
 # -nostdlib -- Don't include the standard library.
 # -mabi=sysv -- Explicitly specify the ABI since we will rely on it.
 # -mno-red-zone -- Don't put data below the stack pointer (clobbered by interrupts).
 # -mcmodel=kernel -- Assume the kernel code is running in the higher half.
 # -mgeneral-regs-only -- Prevent GCC from using a whole host of nonsense registers (that we have to enable).
-# Hopefully preceded by -mgeneral-regs-only
-# -mno-80387
-# -mno-mmx
-# -mno-3dnow
-# -mno-sse -mno-sse2
-# -MMD -- Something with the preprocessor?
-set(_Z_COMPILE_FLAGS "${CMAKE_CXX_FLAGS} -ffreestanding -nostdlib -mabi=sysv -mno-red-zone -mcmodel=kernel -mgeneral-regs-only")
-# -mno-80387 -mno-mmx -mno-3dnow -mno-sse -mno-sse2 -MMD
+set(_Z_COMPILE_FLAGS "${CMAKE_CXX_FLAGS} -c -ffreestanding -nostdlib -mabi=sysv -mno-red-zone -mcmodel=kernel -mgeneral-regs-only")
 
 set(_Z_LINK_SCRIPT "${CMAKE_CURRENT_SOURCE_DIR}/linker.ld")
 

zion/boot/boot_info.cpp

@@ -0,0 +1,28 @@
+#include "boot/boot_info.h"
+
+#include "debug/debug.h"
+
+namespace boot {
+static volatile struct limine_memmap_request gMemmapRequest {
+  .id = LIMINE_MEMMAP_REQUEST, .revision = 0, .response = 0,
+};
+
+const limine_memmap_response& GetMemoryMap() {
+  if (!gMemmapRequest.response) {
+    panic("No memmap from limine.");
+  }
+  return *gMemmapRequest.response;
+}
+
+static volatile struct limine_hhdm_request gHhdmRequest {
+  .id = LIMINE_HHDM_REQUEST, .revision = 0, .response = 0,
+};
+
+uint64_t GetHigherHalfDirectMap() {
+  if (!gHhdmRequest.response) {
+    panic("No HHDM response from limine.");
+  }
+  return gHhdmRequest.response->offset;
+}
+
+}  // namespace boot

zion/boot/boot_info.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include "boot/limine.h"
+
+namespace boot {
+
+const limine_memmap_response& GetMemoryMap();
+uint64_t GetHigherHalfDirectMap();
+
+}  // namespace boot

zion/boot/limine.h

@@ -0,0 +1,461 @@
+// Copied from https://github.com/limine-bootloader/limine/blob/trunk/limine.h
+// TODO:
+
+#pragma once
+
+#include <stdint.h>
+
+extern "C" {
+
+/* Misc */
+
+#ifdef LIMINE_NO_POINTERS
+#define LIMINE_PTR(TYPE) uint64_t
+#else
+#define LIMINE_PTR(TYPE) TYPE
+#endif
+
+#define LIMINE_COMMON_MAGIC 0xc7b1dd30df4c8b88, 0x0a82e883a194f07b
+
+struct limine_uuid {
+  uint32_t a;
+  uint16_t b;
+  uint16_t c;
+  uint8_t d[8];
+};
+
+#define LIMINE_MEDIA_TYPE_GENERIC 0
+#define LIMINE_MEDIA_TYPE_OPTICAL 1
+#define LIMINE_MEDIA_TYPE_TFTP 2
+
+struct limine_file {
+  uint64_t revision;
+  LIMINE_PTR(void *) address;
+  uint64_t size;
+  LIMINE_PTR(char *) path;
+  LIMINE_PTR(char *) cmdline;
+  uint32_t media_type;
+  uint32_t unused;
+  uint32_t tftp_ip;
+  uint32_t tftp_port;
+  uint32_t partition_index;
+  uint32_t mbr_disk_id;
+  struct limine_uuid gpt_disk_uuid;
+  struct limine_uuid gpt_part_uuid;
+  struct limine_uuid part_uuid;
+};
+
+/* Boot info */
+
+#define LIMINE_BOOTLOADER_INFO_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0xf55038d8e2a1202f, 0x279426fcf5f59740 }
+
+struct limine_bootloader_info_response {
+  uint64_t revision;
+  LIMINE_PTR(char *) name;
+  LIMINE_PTR(char *) version;
+};
+
+struct limine_bootloader_info_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_bootloader_info_response *) response;
+};
+
+/* Stack size */
+
+#define LIMINE_STACK_SIZE_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x224ef0460a8e8926, 0xe1cb0fc25f46ea3d }
+
+struct limine_stack_size_response {
+  uint64_t revision;
+};
+
+struct limine_stack_size_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_stack_size_response *) response;
+  uint64_t stack_size;
+};
+
+/* HHDM */
+
+#define LIMINE_HHDM_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x48dcf1cb8ad2b852, 0x63984e959a98244b }
+
+struct limine_hhdm_response {
+  uint64_t revision;
+  uint64_t offset;
+};
+
+struct limine_hhdm_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_hhdm_response *) response;
+};
+
+/* Framebuffer */
+
+#define LIMINE_FRAMEBUFFER_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x9d5827dcd881dd75, 0xa3148604f6fab11b }
+
+#define LIMINE_FRAMEBUFFER_RGB 1
+
+struct limine_framebuffer {
+  LIMINE_PTR(void *) address;
+  uint64_t width;
+  uint64_t height;
+  uint64_t pitch;
+  uint16_t bpp;
+  uint8_t memory_model;
+  uint8_t red_mask_size;
+  uint8_t red_mask_shift;
+  uint8_t green_mask_size;
+  uint8_t green_mask_shift;
+  uint8_t blue_mask_size;
+  uint8_t blue_mask_shift;
+  uint8_t unused[7];
+  uint64_t edid_size;
+  LIMINE_PTR(void *) edid;
+};
+
+struct limine_framebuffer_response {
+  uint64_t revision;
+  uint64_t framebuffer_count;
+  LIMINE_PTR(struct limine_framebuffer **) framebuffers;
+};
+
+struct limine_framebuffer_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_framebuffer_response *) response;
+};
+
+/* Framebuffer (legacy) */
+
+#define LIMINE_FRAMEBUFFER_LEGACY_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0xcbfe81d7dd2d1977, 0x063150319ebc9b71 }
+
+struct limine_framebuffer_legacy {
+  LIMINE_PTR(void *) address;
+  uint16_t width;
+  uint16_t height;
+  uint16_t pitch;
+  uint16_t bpp;
+  uint8_t memory_model;
+  uint8_t red_mask_size;
+  uint8_t red_mask_shift;
+  uint8_t green_mask_size;
+  uint8_t green_mask_shift;
+  uint8_t blue_mask_size;
+  uint8_t blue_mask_shift;
+  uint8_t unused;
+  uint64_t edid_size;
+  LIMINE_PTR(void *) edid;
+};
+
+struct limine_framebuffer_legacy_response {
+  uint64_t revision;
+  uint64_t framebuffer_count;
+  LIMINE_PTR(struct limine_framebuffer_legacy **) framebuffers;
+};
+
+struct limine_framebuffer_legacy_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_framebuffer_legacy_response *) response;
+};
+
+/* Terminal */
+
+#define LIMINE_TERMINAL_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0xc8ac59310c2b0844, 0xa68d0c7265d38878 }
+
+#define LIMINE_TERMINAL_CB_DEC 10
+#define LIMINE_TERMINAL_CB_BELL 20
+#define LIMINE_TERMINAL_CB_PRIVATE_ID 30
+#define LIMINE_TERMINAL_CB_STATUS_REPORT 40
+#define LIMINE_TERMINAL_CB_POS_REPORT 50
+#define LIMINE_TERMINAL_CB_KBD_LEDS 60
+#define LIMINE_TERMINAL_CB_MODE 70
+#define LIMINE_TERMINAL_CB_LINUX 80
+
+#define LIMINE_TERMINAL_CTX_SIZE ((uint64_t)(-1))
+#define LIMINE_TERMINAL_CTX_SAVE ((uint64_t)(-2))
+#define LIMINE_TERMINAL_CTX_RESTORE ((uint64_t)(-3))
+#define LIMINE_TERMINAL_FULL_REFRESH ((uint64_t)(-4))
+
+struct limine_terminal;
+
+typedef void (*limine_terminal_write)(struct limine_terminal *, const char *,
+                                      uint64_t);
+typedef void (*limine_terminal_callback)(struct limine_terminal *, uint64_t,
+                                         uint64_t, uint64_t, uint64_t);
+
+struct limine_terminal {
+  uint64_t columns;
+  uint64_t rows;
+  LIMINE_PTR(struct limine_framebuffer *) framebuffer;
+};
+
+struct limine_terminal_response {
+  uint64_t revision;
+  uint64_t terminal_count;
+  LIMINE_PTR(struct limine_terminal **) terminals;
+  LIMINE_PTR(limine_terminal_write) write;
+};
+
+struct limine_terminal_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_terminal_response *) response;
+  LIMINE_PTR(limine_terminal_callback) callback;
+};
+
+/* Terminal (legacy) */
+
+#define LIMINE_TERMINAL_LEGACY_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x0785a0aea5d0750f, 0x1c1936fee0d6cf6e }
+
+struct limine_terminal_legacy;
+
+typedef void (*limine_terminal_legacy_write)(struct limine_terminal_legacy *,
+                                             const char *, uint64_t);
+typedef void (*limine_terminal_legacy_callback)(struct limine_terminal_legacy *,
+                                                uint64_t, uint64_t, uint64_t,
+                                                uint64_t);
+
+struct limine_terminal_legacy {
+  uint32_t columns;
+  uint32_t rows;
+  LIMINE_PTR(struct limine_framebuffer_legacy *) framebuffer;
+};
+
+struct limine_terminal_legacy_response {
+  uint64_t revision;
+  uint64_t terminal_count;
+  LIMINE_PTR(struct limine_terminal_legacy **) terminals;
+  LIMINE_PTR(limine_terminal_legacy_write) write;
+};
+
+struct limine_terminal_legacy_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_terminal_legacy_response *) response;
+  LIMINE_PTR(limine_terminal_legacy_callback) callback;
+};
+
+/* 5-level paging */
+
+#define LIMINE_5_LEVEL_PAGING_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x94469551da9b3192, 0xebe5e86db7382888 }
+
+struct limine_5_level_paging_response {
+  uint64_t revision;
+};
+
+struct limine_5_level_paging_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_5_level_paging_response *) response;
+};
+
+/* SMP */
+
+#define LIMINE_SMP_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x95a67b819a1b857e, 0xa0b61b723b6a73e0 }
+
+#define LIMINE_SMP_X2APIC (1 << 0)
+
+struct limine_smp_info;
+
+typedef void (*limine_goto_address)(struct limine_smp_info *);
+
+struct limine_smp_info {
+  uint32_t processor_id;
+  uint32_t lapic_id;
+  uint64_t reserved;
+  LIMINE_PTR(limine_goto_address) goto_address;
+  uint64_t extra_argument;
+};
+
+struct limine_smp_response {
+  uint64_t revision;
+  uint32_t flags;
+  uint32_t bsp_lapic_id;
+  uint64_t cpu_count;
+  LIMINE_PTR(struct limine_smp_info **) cpus;
+};
+
+struct limine_smp_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_smp_response *) response;
+  uint64_t flags;
+};
+
+/* Memory map */
+
+#define LIMINE_MEMMAP_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x67cf3d9d378a806f, 0xe304acdfc50c3c62 }
+
+#define LIMINE_MEMMAP_USABLE 0
+#define LIMINE_MEMMAP_RESERVED 1
+#define LIMINE_MEMMAP_ACPI_RECLAIMABLE 2
+#define LIMINE_MEMMAP_ACPI_NVS 3
+#define LIMINE_MEMMAP_BAD_MEMORY 4
+#define LIMINE_MEMMAP_BOOTLOADER_RECLAIMABLE 5
+#define LIMINE_MEMMAP_KERNEL_AND_MODULES 6
+#define LIMINE_MEMMAP_FRAMEBUFFER 7
+
+struct limine_memmap_entry {
+  uint64_t base;
+  uint64_t length;
+  uint64_t type;
+};
+
+struct limine_memmap_response {
+  uint64_t revision;
+  uint64_t entry_count;
+  LIMINE_PTR(struct limine_memmap_entry **) entries;
+};
+
+struct limine_memmap_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_memmap_response *) response;
+};
+
+/* Entry point */
+
+#define LIMINE_ENTRY_POINT_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x13d86c035a1cd3e1, 0x2b0caa89d8f3026a }
+
+typedef void (*limine_entry_point)(void);
+
+struct limine_entry_point_response {
+  uint64_t revision;
+};
+
+struct limine_entry_point_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_entry_point_response *) response;
+  LIMINE_PTR(limine_entry_point) entry;
+};
+
+/* Kernel File */
+
+#define LIMINE_KERNEL_FILE_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0xad97e90e83f1ed67, 0x31eb5d1c5ff23b69 }
+
+struct limine_kernel_file_response {
+  uint64_t revision;
+  LIMINE_PTR(struct limine_file *) kernel_file;
+};
+
+struct limine_kernel_file_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_kernel_file_response *) response;
+};
+
+/* Module */
+
+#define LIMINE_MODULE_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x3e7e279702be32af, 0xca1c4f3bd1280cee }
+
+struct limine_module_response {
+  uint64_t revision;
+  uint64_t module_count;
+  LIMINE_PTR(struct limine_file **) modules;
+};
+
+struct limine_module_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_module_response *) response;
+};
+
+/* RSDP */
+
+#define LIMINE_RSDP_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0xc5e77b6b397e7b43, 0x27637845accdcf3c }
+
+struct limine_rsdp_response {
+  uint64_t revision;
+  LIMINE_PTR(void *) address;
+};
+
+struct limine_rsdp_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_rsdp_response *) response;
+};
+
+/* SMBIOS */
+
+#define LIMINE_SMBIOS_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x9e9046f11e095391, 0xaa4a520fefbde5ee }
+
+struct limine_smbios_response {
+  uint64_t revision;
+  LIMINE_PTR(void *) entry_32;
+  LIMINE_PTR(void *) entry_64;
+};
+
+struct limine_smbios_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_smbios_response *) response;
+};
+
+/* EFI system table */
+
+#define LIMINE_EFI_SYSTEM_TABLE_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x5ceba5163eaaf6d6, 0x0a6981610cf65fcc }
+
+struct limine_efi_system_table_response {
+  uint64_t revision;
+  LIMINE_PTR(void *) address;
+};
+
+struct limine_efi_system_table_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_efi_system_table_response *) response;
+};
+
+/* Boot time */
+
+#define LIMINE_BOOT_TIME_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x502746e184c088aa, 0xfbc5ec83e6327893 }
+
+struct limine_boot_time_response {
+  uint64_t revision;
+  int64_t boot_time;
+};
+
+struct limine_boot_time_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_boot_time_response *) response;
+};
+
+/* Kernel address */
+
+#define LIMINE_KERNEL_ADDRESS_REQUEST \
+  { LIMINE_COMMON_MAGIC, 0x71ba76863cc55f63, 0xb2644a48c516a487 }
+
+struct limine_kernel_address_response {
+  uint64_t revision;
+  uint64_t physical_base;
+  uint64_t virtual_base;
+};
+
+struct limine_kernel_address_request {
+  uint64_t id[4];
+  uint64_t revision;
+  LIMINE_PTR(struct limine_kernel_address_response *) response;
+};
+}

zion/common/gdt.cpp

@@ -0,0 +1,92 @@
+#include "common/gdt.h"
+
+#include <stdint.h>
+
+#define GDT_ACCESSED 1
+#define GDT_READ_WRITE (1 << 1)
+#define GDT_EXECUTABLE (1 << 3)
+#define GDT_SEGMENT (1 << 4)
+#define GDT_RING3 (3 << 5)
+#define GDT_PRESENT (1 << 7)
+
+#define GDT_FLAGS (1 << 7) | (1 << 5)  // 4K granularity | long mode
+
+struct TaskStateSegment {
+  uint32_t reserved = 0;
+  uint64_t rsp0 = 0;
+  uint64_t rsp1 = 0;
+  uint64_t rsp2 = 0;
+  uint64_t reserved2 = 0;
+  uint64_t ist1 = 0;
+  uint64_t ist2 = 0;
+  uint64_t ist3 = 0;
+  uint64_t ist4 = 0;
+  uint64_t ist5 = 0;
+  uint64_t ist6 = 0;
+  uint64_t ist7 = 0;
+  uint64_t reserved3 = 0;
+  uint16_t reserved4 = 0;
+  uint16_t iomap_base = 0;
+} __attribute__((packed));
+
+struct GdtPointer {
+  uint16_t size;
+  uint64_t base;
+} __attribute__((packed));
+
+static uint64_t gGdtSegments[7];
+static TaskStateSegment gTaskStateSegment;
+
+// Defined in load_gdt.s
+extern "C" void ReloadSegments();
+
+uint64_t CreateSegment(uint64_t access, uint64_t flags) {
+  uint64_t base = 0;
+  access &= 0xFF;
+  flags &= 0xF0;
+  flags |= 0xF;  // For the highest 4 bits of the limit.
+  // Lowest bits are the limit (always set to max);
+  return (0xFFFF) | (access << 40) | (flags << 48);
+}
+
+uint64_t CreateTssSegment(TaskStateSegment* tss) {
+  uint64_t base = reinterpret_cast<uint64_t>(tss);
+  uint64_t limit = sizeof(TaskStateSegment);
+  uint64_t access = GDT_ACCESSED | GDT_PRESENT | GDT_EXECUTABLE;
+  return limit | ((base & 0xFFFF) << 16) | ((base >> 16 & 0xFF) << 32) |
+         (access << 40) | (((base >> 24) & 0xFF) << 56);
+}
+
+void InitGdt() {
+  gGdtSegments[0] = CreateSegment(0, 0);
+  uint64_t default_bits = GDT_PRESENT | GDT_SEGMENT | GDT_READ_WRITE;
+
+  // Kernel CS
+  gGdtSegments[1] = CreateSegment(default_bits | GDT_EXECUTABLE, GDT_FLAGS);
+
+  // Kernel DS
+  gGdtSegments[2] = CreateSegment(default_bits, GDT_FLAGS);
+
+  // User CS
+  gGdtSegments[3] =
+      CreateSegment(default_bits | GDT_RING3 | GDT_EXECUTABLE, GDT_FLAGS);
+
+  // User DS
+  gGdtSegments[4] = CreateSegment(default_bits | GDT_RING3, GDT_FLAGS);
+
+  gTaskStateSegment.iomap_base = sizeof(TaskStateSegment);
+  gGdtSegments[5] = CreateTssSegment(&gTaskStateSegment);
+  gGdtSegments[6] = reinterpret_cast<uint64_t>(&gTaskStateSegment) >> 32;
+
+  GdtPointer gdtp{
+      .size = sizeof(gGdtSegments) - 1,
+      .base = reinterpret_cast<uint64_t>(gGdtSegments),
+  };
+
+  asm volatile("lgdt %0" ::"m"(gdtp));
+  ReloadSegments();
+  asm volatile(
+      "mov $0x28, %%ax;"
+      "ltr %%ax;" ::
+          : "rax");
+}

zion/common/gdt.h

@@ -0,0 +1,3 @@
+#pragma once
+
+void InitGdt();

zion/common/load_gdt.s

@@ -0,0 +1,15 @@
+.global ReloadSegments
+ReloadSegments:
+  push $0x08
+  lea ._reload_cs, %rax
+  push %rax
+  retfq
+
+._reload_cs:
+  mov $0x10, %ax
+  mov %ax, %ds
+  mov %ax, %es
+  mov %ax, %fs
+  mov %ax, %gs
+  mov %ax, %ss
+  ret

zion/debug/debug.cpp

@@ -4,10 +4,141 @@
 
 #define COM1 0x3f8
 
-void dbgln(const char* str) {
-  while (*str != 0) {
-    outb(COM1, *str);
-    str++;
-  }
-  outb(COM1, '\n');
+namespace {
+bool is_transmit_empty() { return (inb(COM1 + 5) & 0x20) != 0; }
+
+void dbgputchar(char c) {
+  while (!is_transmit_empty())
+    ;
+
+  outb(COM1, c);
+}
+
+void dbgcstr(const char* str) {
+  for (; *str != '\0'; str++) {
+    dbgputchar(*str);
+  }
+}
+
+void U64ToStr(uint64_t u, char* str) {
+  uint64_t len = 0;
+  uint64_t u2 = u;
+  while (u2 != 0) {
+    len++;
+    u2 /= 10;
+  }
+
+  if (len == 0) {
+    len = 1;
+  }
+
+  str[len] = '\0';
+
+  for (int64_t i = len - 1; i >= 0; i--) {
+    str[i] = (u % 10) + '0';
+    u /= 10;
+  }
+}
+
+void HexToStr(uint64_t u, char* str) {
+  uint64_t len = 0;
+  uint64_t u2 = u;
+  while (u2 != 0) {
+    len++;
+    u2 /= 16;
+  }
+
+  if (len == 0) {
+    len = 1;
+  }
+
+  len += 2;
+  str[0] = '0';
+  str[1] = 'x';
+  str[len] = '\0';
+  const char* hex = "0123456789ABCDEF";
+  for (uint64_t i = len - 1; i > 1; i--) {
+    str[i] = hex[u & 0xF];
+    u >>= 4;
+  }
+}
+
+void MemToStr(uint64_t u, char* str) {
+  str[0] = '0';
+  str[1] = 'x';
+  const char* hex = "0123456789ABCDEF";
+  for (uint64_t i = 0; i < 16; i++) {
+    str[17 - i] = hex[(u >> (i * 4)) & 0xF];
+  }
+  str[18] = '\0';
+}
+
+void dbgln_internal(const char* fmt, va_list args) {
+  for (; *fmt != '\0'; fmt++) {
+    if (*fmt != '%') {
+      dbgputchar(*fmt);
+      continue;
+    }
+    fmt++;
+    switch (*fmt) {
+      case '%':
+        dbgputchar('%');
+        break;
+      case 's': {
+        char* str = va_arg(args, char*);
+        dbgcstr(str);
+        break;
+      }
+      case 'c': {
+        char c = va_arg(args, int);
+        dbgputchar(c);
+        break;
+      }
+      case 'u': {
+        uint64_t u = va_arg(args, uint64_t);
+        char str[21];
+        U64ToStr(u, str);
+        dbgcstr(str);
+        break;
+      }
+      case 'x': {
+        uint64_t u = va_arg(args, uint64_t);
+        char str[19];
+        HexToStr(u, str);
+        dbgcstr(str);
+        break;
+      }
+      case 'm': {
+        uint64_t u = va_arg(args, uint64_t);
+        char str[19];
+        MemToStr(u, str);
+        dbgcstr(str);
+        break;
+      }
+      default: {
+        panic("Bad format char: %c", *fmt);
+      }
+    }
+  }
+  dbgputchar('\n');
+}
+
+}  // namespace
+
+void dbgln(const char* fmt, ...) {
+  va_list arg;
+  va_start(arg, fmt);
+  dbgln_internal(fmt, arg);
+  va_end(arg);
+}
+
+void panic(const char* fmt, ...) {
+  asm volatile("cli");
+  va_list arg;
+  va_start(arg, fmt);
+  dbgln_internal(fmt, arg);
+  va_end(arg);
+  dbgln("PANIC");
+  while (1)
+    ;
 }

zion/debug/debug.h

@@ -1,3 +1,6 @@
 #pragma once
 
-void dbgln(const char *str);
+#include <stdarg.h>
+
+void dbgln(const char* str, ...);
+void panic(const char* str, ...);

zion/interrupt/interrupt.cpp

@@ -0,0 +1,59 @@
+#include "interrupt/interrupt.h"
+
+#include <stdint.h>
+
+#include "debug/debug.h"
+
+#define IDT_INTERRUPT_GATE 0x8E
+
+#define KERNEL_CS 0x8
+
+struct InterruptDescriptorTablePointer {
+  uint16_t size;
+  uint64_t base;
+} __attribute__((packed));
+
+struct InterruptDescriptor {
+  uint16_t offset_low;
+  uint16_t selector;
+  uint8_t ist;
+  uint8_t flags;
+  uint16_t offset_medium;
+  uint32_t offset_high;
+  uint32_t zero;
+} __attribute__((packed));
+
+static InterruptDescriptor gIdt[256];
+
+InterruptDescriptor CreateDescriptor(void isr(void)) {
+  uint64_t offset = reinterpret_cast<uint64_t>(isr);
+  return InterruptDescriptor{
+      .offset_low = static_cast<uint16_t>(offset),
+      .selector = KERNEL_CS,
+      .ist = 0,
+      .flags = IDT_INTERRUPT_GATE,
+      .offset_medium = static_cast<uint16_t>(offset >> 16),
+      .offset_high = static_cast<uint32_t>(offset >> 32),
+      .zero = 0x0,
+  };
+}
+
+extern "C" void isr_divide_by_zero();
+extern "C" void interrupt_divide_by_zero(void* frame) { panic("DIV0"); }
+
+extern "C" void isr_protection_fault();
+extern "C" void interrupt_protection_fault(void* frame) { panic("GP"); }
+
+extern "C" void isr_page_fault();
+extern "C" void interrupt_page_fault(void* frame) { panic("PF"); }
+
+void InitIdt() {
+  gIdt[0] = CreateDescriptor(isr_divide_by_zero);
+  gIdt[13] = CreateDescriptor(isr_protection_fault);
+  gIdt[14] = CreateDescriptor(isr_page_fault);
+  InterruptDescriptorTablePointer idtp{
+      .size = sizeof(gIdt),
+      .base = reinterpret_cast<uint64_t>(gIdt),
+  };
+  asm volatile("lidt %0" ::"m"(idtp));
+}

zion/interrupt/interrupt.h

@@ -0,0 +1,3 @@
+#pragma once
+
+void InitIdt();

zion/interrupt/interrupt_enter.s

@@ -0,0 +1,57 @@
+.macro interrupt_enter
+  push %rbp
+  push %r15
+  push %r14
+  push %r13
+  push %r12
+  push %r11
+  push %r10
+  push %r9
+  push %r8
+  push %rdi
+  push %rsi
+  push %rdx
+  push %rcx  # (Return Address)
+  push %rbx
+  push %rax
+.endm
+
+.macro interrupt_exit
+  pop %rax
+  pop %rbx
+  pop %rcx
+  pop %rdx
+  pop %rsi
+  pop %rdi
+  pop %r8
+  pop %r9
+  pop %r10
+  pop %r10
+  pop %r10
+  pop %r10
+  pop %r10
+  pop %r10
+  pop %rbp
+
+  add $8, %rsp # Remove error code.
+.endm
+
+.macro isr_handler name error_code=0
+.global isr_\name
+isr_\name:
+  .if \error_code
+  .else
+  push $0 # if we don't have an error code, equalize the stack.
+  .endif
+  interrupt_enter
+  sti
+  mov %rsp, %rdi
+  call interrupt_\name
+  cli
+  interrupt_exit
+  iretq
+.endm
+
+isr_handler divide_by_zero
+isr_handler protection_fault,1
+isr_handler page_fault,1

zion/memory/kernel_heap.cpp

@@ -0,0 +1,17 @@
+#include "memory/kernel_heap.h"
+
+#include "debug/debug.h"
+#include "memory/paging_util.h"
+
+KernelHeap::KernelHeap(uint64_t lower_bound, uint64_t upper_bound)
+    : next_addr_(lower_bound), upper_bound_(upper_bound) {}
+
+void* KernelHeap::Allocate(uint64_t size) {
+  if (next_addr_ + size >= upper_bound_) {
+    panic("Kernel Heap Overrun");
+  }
+  EnsureResident(next_addr_, size);
+  uint64_t address = next_addr_;
+  next_addr_ += size;
+  return reinterpret_cast<void*>(address);
+}

zion/memory/kernel_heap.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <stdint.h>
+
+class KernelHeap {
+ public:
+  KernelHeap(uint64_t lower_bound, uint64_t upper_bound);
+
+  void* Allocate(uint64_t size);
+
+ private:
+  uint64_t next_addr_;
+  uint64_t upper_bound_;
+};

zion/memory/paging_util.cpp

@@ -0,0 +1,135 @@
+#include "memory/paging_util.h"
+
+#include "boot/boot_info.h"
+#include "debug/debug.h"
+#include "memory/physical_memory.h"
+
+#define PRESENT_BIT 0x1
+#define READ_WRITE_BIT 0x2
+#define SIGN_EXT 0xFFFF0000'00000000
+#define RECURSIVE ((uint64_t)0x1FE)
+#define PML_OFFSET 39
+#define PDP_OFFSET 30
+#define PD_OFFSET 21
+#define PT_OFFSET 12
+
+// How to recursively index into each page table structure assuming
+// the PML4 is recursively mapped at the 510th entry (0x1FE).
+#define PML_RECURSE 0xFFFFFF7F'BFDFE000
+#define PDP_RECURSE 0xFFFFFF7F'BFC00000
+#define PD_RECURSE 0xFFFFFF7F'80000000
+#define PT_RECURSE 0xFFFFFF00'00000000
+
+namespace {
+
+uint64_t PageAlign(uint64_t addr) { return addr & ~0xFFF; }
+uint64_t* PageAlign(uint64_t* addr) {
+  return reinterpret_cast<uint64_t*>(reinterpret_cast<uint64_t>(addr) & ~0xFFF);
+}
+
+void ZeroOutPage(uint64_t* ptr) {
+  ptr = PageAlign(ptr);
+  for (uint64_t i = 0; i < 512; i++) {
+    ptr[i] = 0;
+  }
+}
+
+uint64_t ShiftForEntryIndexing(uint64_t addr, uint64_t offset) {
+  addr &= ~0xFFFF0000'00000000;
+  addr >>= offset;
+  addr <<= 3;
+  return addr;
+}
+
+void MapPage(uint64_t virt, uint64_t phys) {
+  if (PageLoaded(virt)) {
+    panic("Allocating Over Existing Page: %m", virt);
+  }
+
+  if (!PageDirectoryPointerLoaded(virt)) {
+    uint64_t page = phys_mem::AllocatePage();
+    *Pml4Entry(virt) = page | PRESENT_BIT | READ_WRITE_BIT;
+    ZeroOutPage(PageDirectoryPointerEntry(virt));
+  }
+  if (!PageDirectoryLoaded(virt)) {
+    uint64_t page = phys_mem::AllocatePage();
+    *PageDirectoryPointerEntry(virt) = page | PRESENT_BIT | READ_WRITE_BIT;
+    ZeroOutPage(PageDirectoryEntry(virt));
+  }
+  if (!PageTableLoaded(virt)) {
+    uint64_t page = phys_mem::AllocatePage();
+    *PageDirectoryEntry(virt) = page | PRESENT_BIT | READ_WRITE_BIT;
+    ZeroOutPage(PageTableEntry(virt));
+  }
+
+  *PageTableEntry(virt) = PageAlign(phys) | PRESENT_BIT | READ_WRITE_BIT;
+  ZeroOutPage(reinterpret_cast<uint64_t*>(virt));
+}
+}  // namespace
+
+void InitPaging() {
+  uint64_t pml4_addr = 0;
+  asm volatile("mov %%cr3, %0;" : "=r"(pml4_addr));
+  InitializePml4(pml4_addr);
+}
+
+void InitializePml4(uint64_t pml4_physical_addr) {
+  uint64_t* pml4_virtual = reinterpret_cast<uint64_t*>(
+      boot::GetHigherHalfDirectMap() + pml4_physical_addr);
+
+  uint64_t recursive_entry = pml4_physical_addr | PRESENT_BIT | READ_WRITE_BIT;
+  pml4_virtual[0x1FE] = recursive_entry;
+}
+
+void AllocatePage(uint64_t addr) {
+  uint64_t physical_page = phys_mem::AllocatePage();
+  MapPage(addr, physical_page);
+}
+
+void EnsureResident(uint64_t addr, uint64_t size) {
+  uint64_t max = addr + size;
+  addr = PageAlign(addr);
+  while (addr < max) {
+    if (!PageLoaded(addr)) {
+      AllocatePage(addr);
+    }
+    addr += 0x1000;
+  }
+}
+
+uint64_t* Pml4Entry(uint64_t addr) {
+  return reinterpret_cast<uint64_t*>(PML_RECURSE |
+                                     ShiftForEntryIndexing(addr, PML_OFFSET));
+}
+
+uint64_t* PageDirectoryPointerEntry(uint64_t addr) {
+  return reinterpret_cast<uint64_t*>(PDP_RECURSE |
+                                     ShiftForEntryIndexing(addr, PDP_OFFSET));
+}
+
+uint64_t* PageDirectoryEntry(uint64_t addr) {
+  return reinterpret_cast<uint64_t*>(PD_RECURSE |
+                                     ShiftForEntryIndexing(addr, PD_OFFSET));
+}
+
+uint64_t* PageTableEntry(uint64_t addr) {
+  return reinterpret_cast<uint64_t*>(PT_RECURSE |
+                                     ShiftForEntryIndexing(addr, PT_OFFSET));
+}
+
+bool PageDirectoryPointerLoaded(uint64_t addr) {
+  return *Pml4Entry(addr) & PRESENT_BIT;
+}
+
+bool PageDirectoryLoaded(uint64_t addr) {
+  return PageDirectoryPointerLoaded(addr) &&
+         (*PageDirectoryPointerEntry(addr) & PRESENT_BIT);
+}
+
+bool PageTableLoaded(uint64_t addr) {
+  return PageDirectoryLoaded(addr) && (*PageDirectoryEntry(addr) & PRESENT_BIT);
+}
+
+bool PageLoaded(uint64_t addr) {
+  return PageTableLoaded(addr) && (*PageTableEntry(addr) & PRESENT_BIT);
+}

zion/memory/paging_util.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <stdint.h>
+
+void InitPaging();
+void InitializePml4(uint64_t pml4_physical_addr);
+
+void AllocatePageDirectoryPointer(uint64_t addr);
+void AllocatePageDirectory(uint64_t addr);
+void AllocatePageTable(uint64_t addr);
+void AllocatePage(uint64_t addr);
+void EnsureResident(uint64_t addr, uint64_t size);
+
+uint64_t* Pml4Entry(uint64_t addr);
+uint64_t* PageDirectoryPointerEntry(uint64_t addr);
+uint64_t* PageDirectoryEntry(uint64_t addr);
+uint64_t* PageTableEntry(uint64_t addr);
+
+bool PageDirectoryPointerLoaded(uint64_t addr);
+bool PageDirectoryLoaded(uint64_t addr);
+bool PageTableLoaded(uint64_t addr);
+bool PageLoaded(uint64_t addr);

zion/memory/physical_memory.cpp

@@ -0,0 +1,53 @@
+#include "memory/physical_memory.h"
+
+#include "boot/boot_info.h"
+#include "debug/debug.h"
+
+namespace phys_mem {
+namespace {
+
+struct BootstrapMemory {
+  uint64_t init_page = 0;
+  uint64_t next_page = 0;
+  uint64_t max_page = 0;
+};
+
+static BootstrapMemory gBootstrap;
+static bool gBootstrapEnabled = false;
+
+};  // namespace
+
+void InitBootstrapPageAllocation() {
+  const limine_memmap_response& memmap = boot::GetMemoryMap();
+  for (uint64_t i = 0; i < memmap.entry_count; i++) {
+    const limine_memmap_entry& entry = *memmap.entries[i];
+    // We may want to chose a high address space to not limit
+    // the number of buffers we can allocate later but
+    // if we limit the number of pages this should be fine.
+    // Currently set to the minimum of 3 for one kernel heap allocation:
+    // PageDirectory + PageTable + Page
+    if (entry.type == 0 && entry.length >= 0x3000) {
+      gBootstrap.init_page = entry.base;
+      gBootstrap.next_page = entry.base;
+      gBootstrap.max_page = entry.base + 0x3000;
+      gBootstrapEnabled = true;
+      return;
+    }
+  }
+}
+
+uint64_t AllocatePage() {
+  if (!gBootstrapEnabled) {
+    panic("No Bootstrap Memory Manager");
+  }
+
+  uint64_t page = gBootstrap.next_page;
+  if (page == gBootstrap.max_page) {
+    panic("Bootstrap Memory Manager OOM");
+  }
+  gBootstrap.next_page += 0x1000;
+
+  return page;
+}
+
+}  // namespace phys_mem

zion/memory/physical_memory.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <stdint.h>
+
+namespace phys_mem {
+
+// Called before creating a kernel heap object
+// that allows dynamic allocation. The real
+// PhysicalMemoryManager requires some allocations
+// to initialize so we need this first.
+void InitBootstrapPageAllocation();
+
+void InitPhysicalMemoryManager();
+
+uint64_t AllocatePage();
+void FreePage(uint64_t page);
+
+}  // namespace phys_mem

zion/zion.cpp

@@ -1,10 +1,22 @@
 #include <stdint.h>
 
+#include "common/gdt.h"
 #include "debug/debug.h"
+#include "interrupt/interrupt.h"
+#include "memory/kernel_heap.h"
+#include "memory/paging_util.h"
+#include "memory/physical_memory.h"
 
 extern "C" void zion() {
-  dbgln("Hello World!");
+  InitGdt();
+  InitIdt();
+  InitPaging();
 
+  phys_mem::InitBootstrapPageAllocation();
+  KernelHeap heap(0xFFFFFFFF'40000000, 0xFFFFFFFF'80000000);
+  heap.Allocate(1);
+
+  dbgln("Sleeping!");
   while (1)
     ;
 }