/* * 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) * * BIG FAT NOTE: We're in real mode using 64k segments. Therefore segment * addresses must be multiplied by 16 to obtain their respective linear * addresses. To avoid confusion, linear addresses are written using leading * hex while segment addresses are written as segment:offset. * */ #include #include #include #include #include #include #include "boot.h" #include "voffset.h" #include "zoffset.h" BOOTSEG = 0x07C0 /* original address of boot-sector */ SYSSEG = 0x1000 /* historical load address >> 4 */ #ifndef SVGA_MODE #define SVGA_MODE ASK_VGA #endif #ifndef RAMDISK #define RAMDISK 0 #endif #ifndef ROOT_RDONLY #define ROOT_RDONLY 1 #endif .code16 .section ".bstext", "ax" .global bootsect_start bootsect_start: # Normalize the start address ljmp $BOOTSEG, $start2 start2: movw %cs, %ax movw %ax, %ds movw %ax, %es movw %ax, %ss xorw %sp, %sp sti cld movw $bugger_off_msg, %si msg_loop: lodsb andb %al, %al jz bs_die movb $0xe, %ah movw $7, %bx int $0x10 jmp msg_loop bs_die: # 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 anyway, # invoke the BIOS reset code... ljmp $0xf000,$0xfff0 .section ".bsdata", "a" bugger_off_msg: .ascii "Direct booting from floppy is no longer supported.\r\n" .ascii "Please use a boot loader program instead.\r\n" .ascii "\n" .ascii "Remove disk and press any key to reboot . . .\r\n" .byte 0 # Kernel attributes; used by setup. This is part 1 of the # header, from the old boot sector. .section ".header", "a" .globl hdr hdr: setup_sects: .byte 0 /* Filled in by build.c */ root_flags: .word ROOT_RDONLY syssize: .long 0 /* Filled in by build.c */ ram_size: .word 0 /* Obsolete */ vid_mode: .word SVGA_MODE root_dev: .word 0 /* Filled in by build.c */ boot_flag: .word 0xAA55 # offset 512, entry point .globl _start _start: # Explicitly enter this as bytes, or the assembler # tries to generate a 3-byte jump here, which causes # everything else to push off to the wrong offset. .byte 0xeb # short (2-byte) jump .byte start_of_setup-1f 1: # Part 2 of the header, from the old setup.S .ascii "HdrS" # header signature .word 0x020a # header version number (>= 0x0105) # or else old loadlin-1.5 will fail) .globl realmode_swtch realmode_swtch: .word 0, 0 # default_switch, SETUPSEG start_sys_seg: .word SYSSEG # obsolete and meaningless, but just # in case something decided to "use" it .word kernel_version-512 # pointing to kernel version string # above section of header is compatible # with loadlin-1.5 (header v1.5). Don't # change it. type_of_loader: .byte 0 # 0 means ancient bootloader, newer # bootloaders know to change this. # See Documentation/i386/boot.txt for # assigned ids # flags, unused bits must be zero (RFU) bit within loadflags loadflags: LOADED_HIGH = 1 # If set, the kernel is loaded high CAN_USE_HEAP = 0x80 # If set, the loader also has set # heap_end_ptr to tell how much # space behind setup.S can be used for # heap purposes. # Only the loader knows what is free .byte LOADED_HIGH setup_move_size: .word 0x8000 # size to move, when setup is not # loaded at 0x90000. We will move setup # to 0x90000 then just before jumping # into the kernel. However, only the # loader knows how much data behind # us also needs to be loaded. code32_start: # here loaders can put a different # start address for 32-bit code. .long 0x100000 # 0x100000 = default for big kernel ramdisk_image: .long 0 # address of loaded ramdisk image # Here the loader puts the 32-bit # address where it loaded the image. # This only will be read by the kernel. ramdisk_size: .long 0 # its size in bytes bootsect_kludge: .long 0 # obsolete heap_end_ptr: .word _end+STACK_SIZE-512 # (Header version 0x0201 or later) # space from here (exclusive) down to # end of setup code can be used by setup # for local heap purposes. ext_loader_ver: .byte 0 # Extended boot loader version ext_loader_type: .byte 0 # Extended boot loader type cmd_line_ptr: .long 0 # (Header version 0x0202 or later) # If nonzero, a 32-bit pointer # to the kernel command line. # The command line should be # located between the start of # setup and the end of low # memory (0xa0000), or it may # get overwritten before it # gets read. If this field is # used, there is no longer # anything magical about the # 0x90000 segment; the setup # can be located anywhere in # low memory 0x10000 or higher. ramdisk_max: .long 0x7fffffff # (Header version 0x0203 or later) # The highest safe address for # the contents of an initrd # The current kernel allows up to 4 GB, # but leave it at 2 GB to avoid # possible bootloader bugs. kernel_alignment: .long CONFIG_PHYSICAL_ALIGN #physical addr alignment #required for protected mode #kernel #ifdef CONFIG_RELOCATABLE relocatable_kernel: .byte 1 #else relocatable_kernel: .byte 0 #endif min_alignment: .byte MIN_KERNEL_ALIGN_LG2 # minimum alignment pad3: .word 0 cmdline_size: .long COMMAND_LINE_SIZE-1 #length of the command line, #added with boot protocol #version 2.06 hardware_subarch: .long 0 # subarchitecture, added with 2.07 # default to 0 for normal x86 PC hardware_subarch_data: .quad 0 payload_offset: .long ZO_input_data payload_length: .long ZO_z_input_len setup_data: .quad 0 # 64-bit physical pointer to # single linked list of # struct setup_data pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr #define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_extract_offset) #define VO_INIT_SIZE (VO__end - VO__text) #if ZO_INIT_SIZE > VO_INIT_SIZE #define INIT_SIZE ZO_INIT_SIZE #else #define INIT_SIZE VO_INIT_SIZE #endif init_size: .long INIT_SIZE # kernel initialization size # End of setup header ##################################################### .section ".inittext", "ax" start_of_setup: #ifdef SAFE_RESET_DISK_CONTROLLER # Reset the disk controller. movw $0x0000, %ax # Reset disk controller movb $0x80, %dl # All disks int $0x13 #endif # Force %es = %ds movw %ds, %ax movw %ax, %es cld # Apparently some ancient versions of LILO invoked the kernel with %ss != %ds, # which happened to work by accident for the old code. Recalculate the stack # pointer if %ss is invalid. Otherwise leave it alone, LOADLIN sets up the # stack behind its own code, so we can't blindly put it directly past the heap. movw %ss, %dx cmpw %ax, %dx # %ds == %ss? movw %sp, %dx je 2f # -> assume %sp is reasonably set # Invalid %ss, make up a new stack movw $_end, %dx testb $CAN_USE_HEAP, loadflags jz 1f movw heap_end_ptr, %dx 1: addw $STACK_SIZE, %dx jnc 2f xorw %dx, %dx # Prevent wraparound 2: # Now %dx should point to the end of our stack space andw $~3, %dx # dword align (might as well...) jnz 3f movw $0xfffc, %dx # Make sure we're not zero 3: movw %ax, %ss movzwl %dx, %esp # Clear upper half of %esp sti # Now we should have a working stack # We will have entered with %cs = %ds+0x20, normalize %cs so # it is on par with the other segments. pushw %ds pushw $6f lretw 6: # Check signature at end of setup cmpl $0x5a5aaa55, setup_sig jne setup_bad # Zero the bss movw $__bss_start, %di movw $_end+3, %cx xorl %eax, %eax subw %di, %cx shrw $2, %cx rep; stosl # Jump to C code (should not return) calll main # Setup corrupt somehow... setup_bad: movl $setup_corrupt, %eax calll puts # Fall through... .globl die .type die, @function die: hlt jmp die .size die, .-die .section ".initdata", "a" setup_corrupt: .byte 7 .string "No setup signature found...\n"