bastion: initial implementation

ready project skeleton
dual-arch build system with Linux-config style configuration
UEFI EFI stub loader (PE32+) for x86_64 and AArch64
ELF64 kernel parser
Temporary framebuffer console
freestanding string and c++ abi stubs

For now, kernel boots, prints banner, memory map and go halt

3 files changed, 772 insertions, 0 deletions

diff --git a/include/boot/boot_info.h b/include/boot/boot_info.h
new file mode 100644
index 0000000..cc02ae8
--- /dev/null
+++ b/include/boot/boot_info.h
@@ -0,0 +1,76 @@
+#pragma once
+// ============================================================================
+// boot_info.h - Boot handoff struct
+// Shared between the UEFI loader and the kernel.
+// The loader fills it, the kernel consumes it. Simple.
+// In future i will expand this struct
+// ============================================================================
+
+#include <stdint.h>
+
+// ── Boot Magic Number───────────────────────────────────────────────────────
+inline constexpr uint64_t BOOT_INFO_MAGIC = 0xDEADDEADDEADDEADULL;
+
+// ── Framebuffer (GOP) ───────────────────────────────────────────────────────
+// TODO: remove Framebuffer to driver
+enum class PixelFormat : uint32_t {
+    RGB  = 0,  // PixelRedGreenBlueReserved8BitPerColor
+    BGR  = 1,  // PixelBlueGreenRedReserved8BitPerColor
+    Mask = 2,  // PixelBitMask — need to check masks
+};
+
+struct FramebufferInfo {
+    uint64_t    base;          // Physical address of framebuffer
+    uint32_t    width;         // Horizontal resolution in pixels
+    uint32_t    height;        // Vertical resolution in pixels
+    uint32_t    pitch;         // Bytes per scanline (>= width * 4)
+    PixelFormat format;
+};
+
+// ── Memory map ─────────────────────────────────────────────────────────────
+//TODO: remove FrameBuffer
+enum class MemoryRegionType : uint32_t {
+    Usable                = 0,  // Free RAM - kernel can use
+    Reserved              = 1,  // Firmware/hardware reserved
+    AcpiReclaimable       = 2,  // ACPI tables - free after parsing
+    AcpiNvs               = 3,  // ACPI non-volatile storage
+    BootloaderReclaimable = 4,  // Loader code/data - free after kernel init
+    KernelAndModules      = 5,  // Kernel image + any loaded modules
+    Framebuffer           = 6,  // Framebuffer memory - do not use as RAM
+};
+
+struct MemoryRegion {
+    uint64_t         base;
+    uint64_t         length;
+    MemoryRegionType type;
+    uint32_t         _reserved;  // Padding to 24 bytes
+};
+
+// ── Boot info structure ────────────────────────────────────────────────────
+
+struct BootInfo {
+    uint64_t        magic;               // Must be BOOT_INFO_MAGIC
+
+    // Framebuffer
+    // Todo: remove
+    FramebufferInfo framebuffer;
+
+    // Memory map (array of MemoryRegion)
+    MemoryRegion*   memory_map;
+    uint64_t        memory_map_count;
+
+    // Platform-specific firmware tables (both always present to keep layout uniform)
+    uint64_t        rsdp_address;        // ACPI RSDP (x86_64), 0 if absent
+    uint64_t        fdt_address;         // Flattened Device Tree (aarch64), 0 if absent
+
+    // Kernel load info
+    uint64_t        kernel_phys_base;    // Where the kernel was loaded physically
+    uint64_t        kernel_virt_base;    // Kernel's virtual base (from ELF)
+    uint64_t        kernel_size;         // Total size of kernel in memory
+
+    // Kernel entry point (virtual address from ELF e_entry)
+    uint64_t        kernel_entry_point;
+
+    // Higher-half direct map base (if set up by loader)
+    uint64_t        hhdm_base;           // e.g., 0xFFFF800000000000
+};
diff --git a/include/boot/efi.h b/include/boot/efi.h
new file mode 100644
index 0000000..bcb8854
--- /dev/null
+++ b/include/boot/efi.h
@@ -0,0 +1,365 @@
+#pragma once
+// ============================================================================
+// efi.h - Minimal UEFI type and protocol definitions
+//
+// Only what we need for our boot loader. No external dependencies (like gnu-efi).
+// Reference: UEFI Specification 2.10, https://uefi.org/specs/UEFI/2.10/
+// I generate it with Cloude, because i don't want to manually rewrite whole spec
+// ============================================================================
+
+#include <stdint.h>
+#include <stddef.h>
+
+// ── Base types ─────────────────────────────────────────────────────────────
+
+typedef uint64_t        UINTN;
+typedef int64_t         INTN;
+typedef uint64_t        EFI_STATUS;
+typedef void*           EFI_HANDLE;
+typedef void*           EFI_EVENT;
+typedef uint64_t        EFI_PHYSICAL_ADDRESS;
+typedef uint64_t        EFI_VIRTUAL_ADDRESS;
+typedef wchar_t         CHAR16;  // With -fshort-wchar, wchar_t is 16-bit
+typedef uint8_t         BOOLEAN;
+
+#define TRUE  1
+#define FALSE 0
+#define IN
+#define OUT
+#define OPTIONAL
+#define EFIAPI
+
+// ── Status codes ───────────────────────────────────────────────────────────
+
+#define EFI_SUCCESS              0ULL
+#define EFI_ERROR_BIT            (1ULL << 63)
+#define EFI_LOAD_ERROR           (EFI_ERROR_BIT | 1)
+#define EFI_INVALID_PARAMETER    (EFI_ERROR_BIT | 2)
+#define EFI_UNSUPPORTED          (EFI_ERROR_BIT | 3)
+#define EFI_BAD_BUFFER_SIZE      (EFI_ERROR_BIT | 4)
+#define EFI_BUFFER_TOO_SMALL     (EFI_ERROR_BIT | 5)
+#define EFI_NOT_FOUND            (EFI_ERROR_BIT | 14)
+
+#define EFI_ERROR(status) ((status) & EFI_ERROR_BIT)
+
+// ── GUIDs ──────────────────────────────────────────────────────────────────
+
+struct EFI_GUID {
+    uint32_t Data1;
+    uint16_t Data2;
+    uint16_t Data3;
+    uint8_t  Data4[8];
+};
+
+#define EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID \
+    { 0x9042A9DE, 0x23DC, 0x4A38, { 0x96, 0xFB, 0x7A, 0xDE, 0xD0, 0x80, 0x51, 0x6A } }
+
+#define EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID \
+    { 0x964E5B22, 0x6459, 0x11D2, { 0x8E, 0x39, 0x00, 0xA0, 0xC9, 0x69, 0x72, 0x3B } }
+
+#define EFI_LOADED_IMAGE_PROTOCOL_GUID \
+    { 0x5B1B31A1, 0x9562, 0x11D2, { 0x8E, 0x3F, 0x00, 0xA0, 0xC9, 0x69, 0x72, 0x3B } }
+
+#define EFI_FILE_INFO_ID \
+    { 0x09576E92, 0x6D3F, 0x11D2, { 0x8E, 0x39, 0x00, 0xA0, 0xC9, 0x69, 0x72, 0x3B } }
+
+#define EFI_ACPI_20_TABLE_GUID \
+    { 0x8868E871, 0xE4F1, 0x11D3, { 0xBC, 0x22, 0x00, 0x80, 0xC7, 0x3C, 0x88, 0x81 } }
+
+#define EFI_DTB_TABLE_GUID \
+    { 0xB1B621D5, 0xF19C, 0x41A5, { 0x83, 0x0B, 0xD9, 0x15, 0x2C, 0x69, 0xAA, 0xE0 } }
+
+// ── Memory types ───────────────────────────────────────────────────────────
+
+typedef uint32_t EFI_MEMORY_TYPE;
+#define EfiReservedMemoryType       0
+#define EfiLoaderCode               1
+#define EfiLoaderData               2
+#define EfiBootServicesCode         3
+#define EfiBootServicesData         4
+#define EfiRuntimeServicesCode      5
+#define EfiRuntimeServicesData      6
+#define EfiConventionalMemory       7
+#define EfiUnusableMemory           8
+#define EfiACPIReclaimMemory        9
+#define EfiACPIMemoryNVS            10
+#define EfiMemoryMappedIO           11
+#define EfiMemoryMappedIOPortSpace  12
+#define EfiPalCode                  13
+#define EfiPersistentMemory         14
+#define EfiMaxMemoryType            15
+
+typedef uint32_t EFI_ALLOCATE_TYPE;
+#define AllocateAnyPages    0
+#define AllocateMaxAddress  1
+#define AllocateAddress     2
+
+struct EFI_MEMORY_DESCRIPTOR {
+    uint32_t              Type;
+    EFI_PHYSICAL_ADDRESS  PhysicalStart;
+    EFI_VIRTUAL_ADDRESS   VirtualStart;
+    uint64_t              NumberOfPages;
+    uint64_t              Attribute;
+};
+
+// ── Simple Text Output Protocol ────────────────────────────────────────────
+
+struct EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL {
+    void* Reset;
+    EFI_STATUS (EFIAPI *OutputString)(
+        EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL* This,
+        CHAR16*                         String
+    );
+    void* TestString;
+    void* QueryMode;
+    void* SetMode;
+    void* SetAttribute;
+    EFI_STATUS (EFIAPI *ClearScreen)(
+        EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL* This
+    );
+    void* SetCursorPosition;
+    void* EnableCursor;
+    void* Mode;
+};
+
+// ── Graphics Output Protocol ───────────────────────────────────────────────
+
+typedef uint32_t EFI_GRAPHICS_PIXEL_FORMAT;
+#define PixelRedGreenBlueReserved8BitPerColor  0
+#define PixelBlueGreenRedReserved8BitPerColor  1
+#define PixelBitMask                           2
+#define PixelBltOnly                           3
+
+struct EFI_PIXEL_BITMASK {
+    uint32_t RedMask;
+    uint32_t GreenMask;
+    uint32_t BlueMask;
+    uint32_t ReservedMask;
+};
+
+struct EFI_GRAPHICS_OUTPUT_MODE_INFORMATION {
+    uint32_t                  Version;
+    uint32_t                  HorizontalResolution;
+    uint32_t                  VerticalResolution;
+    EFI_GRAPHICS_PIXEL_FORMAT PixelFormat;
+    EFI_PIXEL_BITMASK         PixelInformation;
+    uint32_t                  PixelsPerScanLine;
+};
+
+struct EFI_GRAPHICS_OUTPUT_PROTOCOL_MODE {
+    uint32_t                              MaxMode;
+    uint32_t                              Mode;
+    EFI_GRAPHICS_OUTPUT_MODE_INFORMATION* Info;
+    UINTN                                 SizeOfInfo;
+    EFI_PHYSICAL_ADDRESS                  FrameBufferBase;
+    UINTN                                 FrameBufferSize;
+};
+
+struct EFI_GRAPHICS_OUTPUT_PROTOCOL {
+    void*                              QueryMode;
+    void*                              SetMode;
+    void*                              Blt;
+    EFI_GRAPHICS_OUTPUT_PROTOCOL_MODE* Mode;
+};
+
+// ── File Protocol ──────────────────────────────────────────────────────────
+
+#define EFI_FILE_MODE_READ   0x0000000000000001ULL
+#define EFI_FILE_READ_ONLY   0x0000000000000001ULL
+
+struct EFI_FILE_PROTOCOL {
+    uint64_t Revision;
+    EFI_STATUS (EFIAPI *Open)(
+        EFI_FILE_PROTOCOL*  This,
+        EFI_FILE_PROTOCOL** NewHandle,
+        CHAR16*             FileName,
+        uint64_t            OpenMode,
+        uint64_t            Attributes
+    );
+    EFI_STATUS (EFIAPI *Close)(
+        EFI_FILE_PROTOCOL* This
+    );
+    void* Delete;
+    EFI_STATUS (EFIAPI *Read)(
+        EFI_FILE_PROTOCOL* This,
+        UINTN*             BufferSize,
+        void*              Buffer
+    );
+    void* Write;
+    void* GetPosition;
+    void* SetPosition;
+    EFI_STATUS (EFIAPI *GetInfo)(
+        EFI_FILE_PROTOCOL* This,
+        EFI_GUID*          InformationType,
+        UINTN*             BufferSize,
+        void*              Buffer
+    );
+};
+
+struct EFI_FILE_INFO {
+    uint64_t Size;
+    uint64_t FileSize;
+    uint64_t PhysicalSize;
+    uint8_t  _time_padding[48];  // Skip EFI_TIME fields
+    uint64_t Attribute;
+    CHAR16   FileName[1];        // Variable length
+};
+
+// ── Simple File System Protocol ────────────────────────────────────────────
+
+struct EFI_SIMPLE_FILE_SYSTEM_PROTOCOL {
+    uint64_t Revision;
+    EFI_STATUS (EFIAPI *OpenVolume)(
+        EFI_SIMPLE_FILE_SYSTEM_PROTOCOL* This,
+        EFI_FILE_PROTOCOL**              Root
+    );
+};
+
+// ── Loaded Image Protocol ──────────────────────────────────────────────────
+
+struct EFI_LOADED_IMAGE_PROTOCOL {
+    uint32_t   Revision;
+    EFI_HANDLE ParentHandle;
+    void*      SystemTable;
+    EFI_HANDLE DeviceHandle;
+    void*      FilePath;
+    void*      Reserved;
+    uint32_t   LoadOptionsSize;
+    void*      LoadOptions;
+    void*      ImageBase;
+    uint64_t   ImageSize;
+    EFI_MEMORY_TYPE ImageCodeType;
+    EFI_MEMORY_TYPE ImageDataType;
+    void*      Unload;
+};
+
+// ── Boot Services ──────────────────────────────────────────────────────────
+
+struct EFI_BOOT_SERVICES {
+    char _hdr[24];
+
+    // Task Priority (2)
+    void* RaiseTPL;
+    void* RestoreTPL;
+
+    // Memory Services
+    EFI_STATUS (EFIAPI *AllocatePages)(
+        EFI_ALLOCATE_TYPE      Type,
+        EFI_MEMORY_TYPE        MemoryType,
+        UINTN                  Pages,
+        EFI_PHYSICAL_ADDRESS*  Memory
+    );
+    EFI_STATUS (EFIAPI *FreePages)(
+        EFI_PHYSICAL_ADDRESS Memory,
+        UINTN                Pages
+    );
+    EFI_STATUS (EFIAPI *GetMemoryMap)(
+        UINTN*                  MemoryMapSize,
+        EFI_MEMORY_DESCRIPTOR*  MemoryMap,
+        UINTN*                  MapKey,
+        UINTN*                  DescriptorSize,
+        uint32_t*               DescriptorVersion
+    );
+    EFI_STATUS (EFIAPI *AllocatePool)(
+        EFI_MEMORY_TYPE PoolType,
+        UINTN           Size,
+        void**          Buffer
+    );
+    EFI_STATUS (EFIAPI *FreePool)(
+        void* Buffer
+    );
+
+    // Event & Timer (6)
+    void* CreateEvent;
+    void* SetTimer;
+    void* WaitForEvent;
+    void* SignalEvent;
+    void* CloseEvent;
+    void* CheckEvent;
+
+    // Protocol Handler (6 + 3)
+    void* InstallProtocolInterface;
+    void* ReinstallProtocolInterface;
+    void* UninstallProtocolInterface;
+    EFI_STATUS (EFIAPI *HandleProtocol)(
+        EFI_HANDLE Handle,
+        EFI_GUID*  Protocol,
+        void**     Interface
+    );
+    void* Reserved;
+    void* RegisterProtocolNotify;
+    void* LocateHandle;
+    void* LocateDevicePath;
+    void* InstallConfigurationTable;
+
+    // Image Services (5)
+    void* LoadImage;
+    void* StartImage;
+    void* Exit;
+    void* UnloadImage;
+    EFI_STATUS (EFIAPI *ExitBootServices)(
+        EFI_HANDLE ImageHandle,
+        UINTN      MapKey
+    );
+
+    // Misc (3)
+    void* GetNextMonotonicCount;
+    void* Stall;
+    void* SetWatchdogTimer;
+
+    // DriverSupport (2)
+    void* ConnectController;
+    void* DisconnectController;
+
+    // Open/Close Protocol (3)
+    void* OpenProtocol;
+    void* CloseProtocol;
+    void* OpenProtocolInformation;
+
+    // Library (3)
+    void* ProtocolsPerHandle;
+    void* LocateHandleBuffer;
+    EFI_STATUS (EFIAPI *LocateProtocol)(
+        EFI_GUID* Protocol,
+        void*     Registration,
+        void**    Interface
+    );
+};
+
+// ── Configuration Table ────────────────────────────────────────────────────
+
+struct EFI_CONFIGURATION_TABLE {
+    EFI_GUID VendorGuid;
+    void*    VendorTable;
+};
+
+// ── System Table ───────────────────────────────────────────────────────────
+
+struct EFI_SYSTEM_TABLE {
+    char _hdr[24];
+
+    CHAR16*                          FirmwareVendor;
+    uint32_t                         FirmwareRevision;
+    uint32_t                         _pad;
+
+    EFI_HANDLE                       ConsoleInHandle;
+    void*                            ConIn;
+    EFI_HANDLE                       ConsoleOutHandle;
+    EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL*  ConOut;
+    EFI_HANDLE                       StandardErrorHandle;
+    void*                            StdErr;
+    void*                            RuntimeServices;
+    EFI_BOOT_SERVICES*               BootServices;
+    UINTN                            NumberOfTableEntries;
+    EFI_CONFIGURATION_TABLE*         ConfigurationTable;
+};
+
+// ── Utility ────────────────────────────────────────────────────────────────
+
+inline bool guid_equal(const EFI_GUID& a, const EFI_GUID& b) {
+    return a.Data1 == b.Data1 && a.Data2 == b.Data2 && a.Data3 == b.Data3 &&
+           a.Data4[0] == b.Data4[0] && a.Data4[1] == b.Data4[1] &&
+           a.Data4[2] == b.Data4[2] && a.Data4[3] == b.Data4[3] &&
+           a.Data4[4] == b.Data4[4] && a.Data4[5] == b.Data4[5] &&
+           a.Data4[6] == b.Data4[6] && a.Data4[7] == b.Data4[7];
+}
diff --git a/include/elf/elf.h b/include/elf/elf.h
new file mode 100644
index 0000000..512ba14
--- /dev/null
+++ b/include/elf/elf.h
@@ -0,0 +1,331 @@
+#pragma once
+
+// ============================================================================
+// elf.h - ELF format definitions
+// https://refspecs.linuxbase.org/elf/elf.pdf
+// https://gist.github.com/x0nu11byt3/bcb35c3de461e5fb66173071a2379779
+// https://docs.oracle.com/cd/E19683-01/816-1386/6m7qcoblh/index.html
+// ============================================================================
+
+#include <stdint.h>
+
+/* ELF Types */
+#pragma message("TODO: describe ELF types from specification")
+
+// ============================================================================
+// =================================== ELF Header =============================
+// ============================================================================
+#define EI_NIDENT (16)
+
+/* e_ident offset (https://en.wikipedia.org/wiki/Executable_and_Linkable_Format#ELF_header) */
+#define EI_MAG0         0
+#define EI_MAG1         1
+#define EI_MAG2         2
+#define EI_MAG3         3
+#define EI_CLASS        4
+#define EI_DATA         5
+#define EI_VERSION      6
+#define EI_OSABI        7
+#define EI_ABIVERSION   8
+#define EI_PAD          9
+
+/* ELF Magic value */
+#define ELF_MAGIC 0x464C457F  // "\x7FELF" little-endian
+
+/* ELF Class */
+#define ELFCLASS32   0x1
+#define ELFCLASS64   0x2
+
+/* Data format: or LSB(Least Significant Bit, little-endian) or MSB(Most Significant Bit, big-endian) */
+#define ELFDATA2LSB  0x1
+#define ELFDATA2MSB  0x2
+
+/* ELF version */
+#define ELFVERSION   0x1
+
+/* Target ABI */
+#define ELFABISYSTEMV   0x00
+#define ELFABIHPUX      0x01
+#define ELFABINETBSD    0x02
+#define ELFABILINUX     0x03
+#define ELFABIGNUHURD   0x04
+#define ELFABISOLARIS   0x06
+#define ELFABIAIX       0x07
+#define ELFABIIRIX      0x08
+#define ELFABIFREEBSD   0x09
+#define ELFABITRU64     0x0A
+#define ELFABINM        0x0B
+#define ELFABIOPENBSD   0x0C
+#define ELFABIOPENVMS   0x0D
+#define ELFABINSKERNEL  0x0E
+#define ELFABIAROS      0x0F
+#define ELFABIFENIXOS   0x10
+#define ELFABICLOUDABI  0x11
+#define ELFABISTOPENVOS 0x12
+
+/* ABI version */
+#pragma message("TODO: do something with ABI version")
+/* Currently i don't use ABI version */
+
+/* Object File Types, e_type field */
+#define ET_NONE     0x0    /* Unknown */
+#define ET_REL      0x1    /* Relocatable. (output of gcc -c). Contains sections + symbol tables + relocations. No program header */
+#define ET_EXEC     0x2    /* Executable. Statically-linked executable with fixed virtual addresses. Has program headers. */
+#define ET_DYN      0x3    /* Shared object. Shared library or PIE executable. Postitoin-independent, relocated at load time. */
+#define ET_CORE     0x4    /* Core dump. Process memory image for post-mortem debugging */
+#define ET_LOOS     0xFE00 /* Reserved inclusive range. Operating system specific */
+#define ET_HIOS     0xFEFF /* Reserved inclusive range. Operating system specific */
+#define ET_LOPROC   0xFF00 /* Reserved inclusive range. Processor specific */
+#define ET_HIPROC   0xFFFF /* Reserved inclusive range. Processor specific */
+
+/* Arch types, e_machine field */
+#pragma message("TODO: add other architecture defines, copy from github")
+#define EM_X86      0x03
+#define EM_X86_64   0x3E
+#define EM_ARM      0x28 /* up to Armv7/AArch32 */
+#define EM_AARCH64  0xB7 /* Armv8/AArch64 */
+
+/* Version value, e_version field */
+#define EV_NONE     0x00
+#define EV_CURRENT  0x01
+#define EV_NUM      0x02
+
+/* Other header fields: 
+    e_entry: Memory address of the entry point.
+    e_phoff: Pointer to the start of the program header table.
+    e_shoff: Pointer to the start of section header table.
+    e_flags: Interpretation of this field depends on the target arch.
+    e_ehsize: Contains the size of header (normally 64 bytes for 64-bit and 52 Bytes for 32-bit)
+    e_phentsize: Contains the size of program header table entry. Or 0x20 (for 32-bit) or 0x38 (for 64-bit).
+    e_phnum: Contains the number of entries in the program header table.
+    e_shentsize: Contains the size of a section header table entry. Or 0x28 (for 32-bit) or 0x40 (for 64-bit)
+    e_shnum: Contains the number of entries in the section header table.
+    e_shstrndx: Contains index of the section header table entry, that contains the section names.
+*/
+
+/* ELF header (atm only for 64 bit) */
+#pragma message("TODO: add elf header for 32 bit")
+struct Elf64_Ehdr {
+    uint8_t  e_ident[EI_NIDENT];
+    uint16_t e_type;
+    uint16_t e_machine;
+    uint32_t e_version;
+    uint64_t e_entry;
+    uint64_t e_phoff;
+    uint64_t e_shoff;
+    uint32_t e_flags;
+    uint16_t e_ehsize;
+    uint16_t e_phentsize;
+    uint16_t e_phnum;
+    uint16_t e_shentsize;
+    uint16_t e_shnum;
+    uint16_t e_shstrndx;
+};
+
+// ============================================================================
+// =================================== Program Header =========================
+// ============================================================================
+
+/* Type, p_type field */
+#define PT_NULL         0x00000000 /* Program header table entry unused */
+#define PT_LOAD         0x00000001 /* Loadable segment */
+#define PT_DYNAMIC      0x00000002 /* Dynamic linking information */
+#define PT_INTERP       0x00000003 /* Interpreter information */
+#define PT_NOTE         0x00000004 /* Auxiliary information */
+#define PT_SHLIB        0x00000005 /* Reserved */
+#define PT_PHDR         0x00000006 /* Segment containing program header table itself */
+#define PT_TLS          0x00000007 /* Thread-Local Storage template */
+#define PT_NUM          0x00000008 /* Number of defined types */
+#define PT_LOOS         0x60000000 /* Reserved inclusive range. Operating system specific: */
+#define PT_GNU_EH_FRAME	0x6474e550	/* GCC .eh_frame_hdr segment */
+#define PT_GNU_STACK	0x6474e551	/* Indicates stack executability */
+#define PT_GNU_RELRO	0x6474e552	/* Read-only after relocation */
+#define PT_LOSUNW	    0x6ffffffa
+#define PT_SUNWBSS	    0x6ffffffa	/* Sun Specific segment */
+#define PT_SUNWSTACK	0x6ffffffb	/* Stack segment */
+#define PT_HISUNW	    0x6fffffff
+#define PT_HIOS         0x6FFFFFFF /* Reserved inclusive range. Operating system specific end*/
+#define PT_LOPROC       0x70000000 /* Reserved inclusive range. Processor specific */
+#define PT_HIPROC       0x7FFFFFFF /* Reserved inclusive range. Processor specific */
+
+/* Flags, p_flags 64-bit field */
+#define PF_X        0x1 /* Executable segment */
+#define PF_W        0x2 /* Writeable segment */
+#define PF_R        0x4 /* Readable segment */
+#define PF_MASKOS   0x0FF00000 /* OS-specific */
+#define PF_MASKPROC 0xF0000000 /* Processor-specific */
+
+/* Other Program Header fields:
+    p_offset: Offset of the segment in the file image.
+    p_vaddr: Virtual address of the segment in memory.
+    p_paddr: On systems where physical address is relevant, reserved for segment's physical address.
+    p_filesz: Size in bytes of the segment in the file image. May be 0.
+    p_memsz: Size in bytes of the segment in memory. May be 0.
+    p_flags: 32-bit flags (don't exist on 64 bit header)
+    p_align: 0 and 1 specify no alignment. Otherwise should be a positive, integral power of 2, with p_vaddr equating p_offset modules p_align
+*/
+
+/* Elf64 Program Header */
+struct Elf64_Phdr {
+    uint32_t p_type;
+    uint32_t p_flags;
+    uint64_t p_offset;
+    uint64_t p_vaddr;
+    uint64_t p_paddr;
+    uint64_t p_filesz;
+    uint64_t p_memsz;
+    uint64_t p_align;
+};
+
+// ============================================================================
+// =================================== Section Header =============================
+// ============================================================================
+
+/* Section Header Type, sh_type field  */
+#define SHT_NULL            0x0 /* Section header table entry unused. First entry in the section table must be SHT_NULL according the stanard */
+#define SHT_PROGBITS        0x1 /* Program data */
+#define SHT_SYMTAB          0x2 /* Symbol table */
+#define SHT_STRTAB          0x3 /* String table */
+#define SHT_RELA            0x4 /* Relocation entries with addends */
+#define SHT_HASH            0x5 /* Symbol hash table */
+#define SHT_DYNAMIC         0x6 /* Dynamic linking information */
+#define SHT_NOTE            0x7 /* Notes */
+#define SHT_NOBITS          0x8 /* Program space with no data (bss) */
+#define SHT_REL             0x9 /* Relocation entries, no addends */
+#define SHT_SHLIB           0x0A /* Reserved */
+#define SHT_DYNSYM          0x0B /* Dynamic linker symbol table */
+#define SHT_INIT_ARRAY      0x0E /* Array of constructors */
+#define SHT_FINI_ARRAY      0x0F /* Array of destructors */
+#define SHT_PREINIT_ARRAY   0x10 /* Array of pre-constructors */
+#define SHT_GROUP           0x11 /* Section group */
+#define SHT_SYMTAB_SHNDX    0x12 /* Extended section indices */
+#define SHT_NUM             0x13 /* Number of defined types */
+#define SHT_LOOS            0x60000000 /* Start OS-specific */
+#define SHT_GNU_ATTRIBUTES  0x6ffffff5	/* Object attributes.  */
+#define SHT_GNU_HASH	    0x6ffffff6	/* GNU-style hash table.  */
+#define SHT_GNU_LIBLIST	    0x6ffffff7	/* Prelink library list */
+#define SHT_CHECKSUM	    0x6ffffff8	/* Checksum for DSO content.  */
+#define SHT_LOSUNW	        0x6ffffffa	/* Sun-specific low bound.  */
+#define SHT_SUNW_move	    0x6ffffffa
+#define SHT_SUNW_COMDAT     0x6ffffffb
+#define SHT_SUNW_syminfo    0x6ffffffc
+#define SHT_GNU_verdef	    0x6ffffffd	/* Version definition section.  */
+#define SHT_GNU_verneed	    0x6ffffffe	/* Version needs section.  */
+#define SHT_GNU_versym	    0x6fffffff	/* Version symbol table.  */
+#define SHT_HISUNW	        0x6fffffff	/* Sun-specific high bound.  */
+#define SHT_HIOS	        0x6fffffff	/* End OS-specific type */
+#define SHT_LOPROC	        0x70000000	/* Start of processor-specific */
+#define SHT_HIPROC	        0x7fffffff	/* End of processor-specific */
+#define SHT_LOUSER	        0x80000000	/* Start of application-specific */
+#define SHT_HIUSER	        0x8fffffff	/* End of application-specific */
+
+/* Section Header flags, sh_flags field */
+#define SHF_WRITE               0x1 /*Writable*/
+#define SHF_ALLOC               0x2 /*Occupies memory during execution*/
+#define SHF_EXECINSTR           0x4 /*Executable*/
+#define SHF_MERGE               0x10 /*Might be merged*/
+#define SHF_STRINGS             0x20 /*Contains null-terminated strings*/
+#define SHF_INFO_LINK           0x40 /*'sh_info' contains SHT index*/
+#define SHF_LINK_ORDER          0x80 /*Preserve order after combining*/
+#define SHF_OS_NONCONFORMING    0x100 /*Non-standard OS specific handling required*/
+#define SHF_GROUP               0x200 /*Section is member of a group*/
+#define SHF_TLS                 0x400 /*Section hold thread-local data*/
+#define SHF_COMPRESSED          0x800 /*Section with compressed data*/
+#define SHF_MASKOS              0x0FF00000 /*OS-specific*/
+#define SHF_MASKPROC            0xF0000000 /*Processor-specific*/
+#define SHF_ORDERED             0x4000000 /*Special ordering requirement (Solaris)*/
+#define SHF_EXCLUDE             0x8000000 /*Section is excluded unless referenced or allocated (Solaris)*/
+
+/* Other Section Header fields:
+    sh_name: An offset to a string in the .shstrab section that represents the name of this section. Zero means no name.
+    sh_addr: Virtual address of the section in memory, for sections that are loaded.
+    sh_offset: Offset of the section in the file image.
+    sh_size: Size in bytes of the section. May be 0.
+    sh_link: Contains the section index of an associated section. This field is used for several purposes, depending on the type of section.
+    sh_info: Contains extra information about the section. This field is used for several purposes, depending on the type of section.
+    sh_addralign: Contains the required alignment of the section. This field must be a power of two.
+    sh_entsize: Contains the size, in bytes, of each entry, for sections that contain fixed-size entries. Otherwise, this field contains zero.
+*/
+/*
+    The most common ELF sections:
+    .text - contains executable code. Packed with Read and Execute flags. Load only one times. Can't be changed.
+    .data - initalized data. Read and Write flags.
+    .rodata - initalized read only data. Read flag.
+    .bss - unititlized data. Read and Write flags.
+    other sections you can see here: https://gist.github.com/x0nu11byt3/bcb35c3de461e5fb66173071a2379779#sections
+
+    Also, there is something like "group of sections" (readelf -g), but it's very rare.
+*/
+
+/* Elf64 Section Header */
+struct Elf64_Shdr {
+    uint32_t sh_name;
+    uint32_t sh_type;
+    uint64_t sh_flags;
+    uint64_t sh_addr;
+    uint64_t sh_offset;
+    uint64_t sh_size;
+    uint32_t sh_link;
+    uint32_t sh_info;
+    uint64_t sh_addralign;
+    uint64_t sh_entsize;
+};
+
+// ============================================================================
+// =================================== Symbols ================================
+// ============================================================================
+// https://docs.oracle.com/cd/E19683-01/816-1386/chapter6-79797/index.html
+#pragma message("TODO: do")
+
+/*  Symbol fields:
+    st_name: Symbol name
+    st_info: Symbol type and binding. It is calculated using macros
+    st_other: Symbol visibility.
+    st_shndx: Section index.
+    st_value: Symbol value.
+    st_size: Symbol size;
+*/
+
+/* Symbol struct */
+struct Elf64_Sym {
+    uint32_t st_name;
+    uint8_t st_info;
+    uint8_t st_other;
+    uint16_t st_shndx;
+    uint64_t st_value;
+    uint64_t st_size;
+};
+
+
+// ============================================================================
+// =================================== ELF Page size ==========================
+// ============================================================================
+#define ELF_PAGE_SIZE   0x1000
+#define ELF_PAGE_MASK   (ELF_PAGE_SIZE - 1)
+
+// ============================================================================
+// =================================== ELF Load Result ========================
+// ============================================================================
+// ATM it uses in efi_elf_parser.cpp
+
+/* Error codes for ElfLoadResult.error */
+#define ELF_ERR_NONE           0  /* success */
+#define ELF_ERR_FILE_TOO_SMALL 1 /* file smaller than ELF header */
+#define ELF_ERR_INVALID_MAGIC  2 /* bad magic */
+#define ELF_ERR_INVALID_CLASS  3 /* bad class */
+#define ELF_ERR_INVALID_IDENT  4 /* bad ident */
+#define ELF_ERR_INVALID_ARCH   5 /* bad machine */
+#define ELF_ERR_INVALID_TYPE   6 /* bad type */
+#define ELF_ERR_NO_LOAD_SEGS   7 /* no PT_LOAD segments found */
+#define ELF_ERR_ALLOC_FAILED   8 /* AllocatePages failed (check efi_alloc_status) */
+
+/* Elf Load Result object */
+struct ElfLoadResult {
+    uint64_t entry_point;
+    uint64_t phys_base;
+    uint64_t virt_base;
+    uint64_t total_size;
+    uint64_t efi_alloc_status; /* EFI_STATUS from AllocatePages, valid when error == ELF_ERR_ALLOC_FAILED */
+    uint8_t  error;            /* ELF_ERR_* code above */
+    bool     success;
+};