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// SPDX-License-Identifier: GPL-2.0
//
// header.S supports booting directly from a UEFI BIOS or via an intermediate
// bootloader that supports the Linux boot protocol. When booted directly from
// the BIOS, it provides the MS-DOS & PE/COFF headers. When using an intermediate
// bootloader, it provides the first few bytes of the Linux boot header (at the
// end of the boot sector), with the remainder of the header being provided by
// setup.S.
//
// Copyright (C) 2020-2023 Martin Whitaker.
//
// Derived from Linux 5.6 arch/x86/boot/header.S:
//
// Copyright (C) 1991, 1992 Linus Torvalds
//
// Based on bootsect.S and setup.S
// modified by more people than can be counted
//
// Rewritten as a common file by H. Peter Anvin (Apr 2007)
#define __ASSEMBLY__
#include "boot.h"
#include "peimage.h"
# The EFI loader loads the header at ImageBase, so we have to locate the main program
# after that. This means we can't load the main program at HIGH_LOAD_ADDR. Pick a load
# address well away from HIGH_LOAD_ADDR, to avoid overlap when relocating the code.
#define IMAGE_BASE 0x200000
.section ".header", "ax", @progbits
.code16
.globl boot
boot:
# "MZ", the MS-DOS header signature.
.byte 0x4d
.byte 0x5a
# In case we are booted by a legacy BIOS, print an error message.
# Fortunately the MS-DOS header translates to harmless instructions.
ljmp $BOOT_SEG, $(error - boot)
error:
movw %cs, %ax
movw %ax, %ds
movw %ax, %es
movw %ax, %ss
xorw %sp, %sp
sti
cld
movw $error_msg, %si
0: lodsb
andb %al, %al
jz wait
movb $0xe, %ah
movw $7, %bx
int $0x10
jmp 0b
wait:
# Allow the user to press a key, then reboot.
xorw %ax, %ax
int $0x16
int $0x19
# int 0x19 should never return. In case it does, invoke the BIOS.
# reset code.
ljmp $0xf000,$0xfff0
# The PE header pointer.
.org 0x3c
.long pe_header
error_msg:
.ascii "This is a UEFI bootable image\r\n"
.ascii "\n"
.asciz "Press any key to reboot\r\n"
pe_header:
.ascii "PE"
.word 0
coff_header:
#ifdef __x86_64__
.word IMAGE_FILE_MACHINE_X64 # Machine (x86-64)
#else
.word IMAGE_FILE_MACHINE_I386 # Machine (i386)
#endif
.word 3 # NumberOfSections
.long 0 # TimeDateStamp
.long 0 # PointerToSymbolTable
.long 0 # NumberOfSymbols
.word section_table - optional_header # SizeOfOptionalHeader
#ifdef __x86_64__
.word IMAGE_FILE_DEBUG_STRIPPED \
| IMAGE_FILE_LOCAL_SYMS_STRIPPED \
| IMAGE_FILE_LINE_NUMS_STRIPPED \
| IMAGE_FILE_EXECUTABLE_IMAGE # Characteristics
#else
.word IMAGE_FILE_32BIT_MACHINE \
| IMAGE_FILE_DEBUG_STRIPPED \
| IMAGE_FILE_LOCAL_SYMS_STRIPPED \
| IMAGE_FILE_LINE_NUMS_STRIPPED \
| IMAGE_FILE_EXECUTABLE_IMAGE # Characteristics.
#endif
optional_header:
#ifdef __x86_64__
.word IMAGE_NT_OPTIONAL_HDR64_MAGIC # PE32+ format
#else
.word IMAGE_NT_OPTIONAL_HDR32_MAGIC # PE32 format
#endif
.byte 0x02 # MajorLinkerVersion
.byte 0x14 # MinorLinkerVersion
.long _virt_text_size # SizeOfCode
.long _virt_sbat_size # SizeOfInitializedData
.long 0 # SizeOfUninitializedData
.long _virt_text_start + 0x1e0 # AddressOfEntryPoint
.long _virt_text_start # BaseOfCode
#ifndef __x86_64__
.long _virt_sbat_start # BaseOfData
#endif
extra_header_fields:
#ifdef __x86_64__
.quad IMAGE_BASE # ImageBase
#else
.long IMAGE_BASE # ImageBase
#endif
.long 4096 # SectionAlignment
.long 512 # FileAlignment
.word 0 # MajorOperatingSystemVersion
.word 0 # MinorOperatingSystemVersion
.word 0 # MajorImageVersion
.word 0 # MinorImageVersion
.word 0 # MajorSubsystemVersion
.word 0 # MinorSubsystemVersion
.long 0 # Win32VersionValue
.long _virt_img_size # SizeOfImage
.long _file_head_size # SizeOfHeaders
.long 0 # CheckSum
.word 10 # Subsystem (EFI application)
.word 0 # DllCharacteristics
#ifdef __x86_64__
.quad 0 # SizeOfStackReserve
.quad 0 # SizeOfStackCommit
.quad 0 # SizeOfHeapReserve
.quad 0 # SizeOfHeapCommit
#else
.long 0 # SizeOfStackReserve
.long 0 # SizeOfStackCommit
.long 0 # SizeOfHeapReserve
.long 0 # SizeOfHeapCommit
#endif
.long 0 # LoaderFlags
.long IMAGE_DIRECTORY_ENTRY_DEBUG # NumberOfRvaAndSizes
.long 0 # DataDirectory.Export.VirtualAddress
.long 0 # DataDirectory.Export.Size
.long 0 # DataDirectory.Import.VirtualAddress
.long 0 # DataDirectory.Import.Size
.long 0 # DataDirectory.Resource.VirtualAddress
.long 0 # DataDirectory.Resource.Size
.long 0 # DataDirectory.Exception.VirtualAddress
.long 0 # DataDirectory.Exception.Size
.long 0 # DataDirectory.Certs.VirtualAddress
.long 0 # DataDirectory.Certs.Size
.long _virt_reloc_start # DataDirectory.BaseReloc.VirtualAddress
.long _real_reloc_size # DataDirectory.BaseReloc.Size
# Section table
section_table:
.ascii ".text"
.byte 0
.byte 0
.byte 0
.long _virt_text_size # VirtualSize
.long _virt_text_start # VirtualAddress
.long _file_text_size # SizeOfRawData
.long _file_text_start # PointerToRawData
.long 0 # PointerToRelocations
.long 0 # PointerToLineNumbers
.word 0 # NumberOfRelocations
.word 0 # NumberOfLineNumbers
.long IMAGE_SCN_MEM_READ \
| IMAGE_SCN_MEM_EXECUTE \
| IMAGE_SCN_CNT_CODE # Characteristics (section flags)
.ascii ".reloc"
.byte 0
.byte 0
.long _virt_reloc_size # VirtualSize
.long _virt_reloc_start # VirtualAddress
.long _file_reloc_size # SizeOfRawData
.long _file_reloc_start # PointerToRawData
.long 0 # PointerToRelocations
.long 0 # PointerToLineNumbers
.word 0 # NumberOfRelocations
.word 0 # NumberOfLineNumbers
.long IMAGE_SCN_MEM_READ \
| IMAGE_SCN_CNT_INITIALIZED_DATA # Characteristics (section flags)
.ascii ".sbat"
.byte 0
.byte 0
.byte 0
.long _virt_sbat_size # VirtualSize
.long _virt_sbat_start # VirtualAddress
.long _file_sbat_size # SizeOfRawData
.long _file_sbat_start # PointerToRawData
.long 0 # PointerToRelocations
.long 0 # PointerToLineNumbers
.word 0 # NumberOfRelocations
.word 0 # NumberOfLineNumbers
.long IMAGE_SCN_MEM_READ \
| IMAGE_SCN_CNT_INITIALIZED_DATA # Characteristics (section flags)
# Emulate the Linux boot header, to allow loading by intermediate boot loaders.
.org 497
setup_sects:
.byte SETUP_SECS
root_flags:
.word 0
sys_size:
.long _sys_size
ram_size:
.word 0
vid_mode:
.word 0
root_dev:
.word 0
boot_flag:
.word 0xAA55
.org 512
.section ".reloc"
.long 0 // Page RVA
.long 10 // Block Size (2*4+2)
.word (IMAGE_REL_BASED_ABSOLUTE << 12) + 0 // reloc 0 -> 0
.section ".sbat", "a", @progbits
.incbin "../boot/sbat.csv"
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