/*******************************************************************************/ /* COS2000 - Compatible Operating System - LGPL v3 - Hordé Nicolas */ /* */ /* Modifié depuis 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 "voffset.h" #include "zoffset.h" SEGBOOT = 0x07C0 SEGSYS = 0x1000 STACK_SIZE = 1024 .code16 .section ".bstext", "ax" .global bootsectstart bootsectstart: ljmp $SEGBOOT, $start2 start2: movw %cs, %ax movw %ax, %ds movw %ax, %es movw %ax, %ss xorw %sp, %sp sti cld movw $msgtxt, %si msg: lodsb andb %al, %al jz dienow movb $0xe, %ah movw $7, %bx int $0x10 jmp msg dienow: xorw %ax, %ax int $0x16 int $0x19 ljmp $0xf000,$0xfff0 .section ".bsdata", "a" msgtxt: .ascii "Utilisez un chargeur de demarrage !\r\n\r\n" .byte 0 .section ".header", "a" .globl sentinel sentinel: .byte 0xff, 0xff .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: .byte 0xeb # short (2-byte) jump .byte setup-1f 1: .ascii "HdrS" # header signature .word 0x020d # 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 SEGSYS # 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/x86/boot.txt for # assigned ids # flags, unused bits must be zero (RFU) bit within loadflags loadflags: .byte LOADED_HIGH # The kernel is to be 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. initrd_addr_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 relocatable_kernel: .byte 0 min_alignment: .byte MIN_KERNEL_ALIGN_LG2 # minimum alignment xloadflags: .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 # # Getting to provably safe in-place decompression is hard. Worst case # behaviours need to be analyzed. Here let's take the decompression of # a gzip-compressed kernel as example, to illustrate it: # # The file layout of gzip compressed kernel is: # # magic[2] # method[1] # flags[1] # timestamp[4] # extraflags[1] # os[1] # compressed data blocks[N] # crc[4] orig_len[4] # # ... resulting in +18 bytes overhead of uncompressed data. # # (For more information, please refer to RFC 1951 and RFC 1952.) # # Files divided into blocks # 1 bit (last block flag) # 2 bits (block type) # # 1 block occurs every 32K -1 bytes or when there 50% compression # has been achieved. The smallest block type encoding is always used. # # stored: # 32 bits length in bytes. # # fixed: # magic fixed tree. # symbols. # # dynamic: # dynamic tree encoding. # symbols. # # # The buffer for decompression in place is the length of the uncompressed # data, plus a small amount extra to keep the algorithm safe. The # compressed data is placed at the end of the buffer. The output pointer # is placed at the start of the buffer and the input pointer is placed # where the compressed data starts. Problems will occur when the output # pointer overruns the input pointer. # # The output pointer can only overrun the input pointer if the input # pointer is moving faster than the output pointer. A condition only # triggered by data whose compressed form is larger than the uncompressed # form. # # The worst case at the block level is a growth of the compressed data # of 5 bytes per 32767 bytes. # # The worst case internal to a compressed block is very hard to figure. # The worst case can at least be bounded by having one bit that represents # 32764 bytes and then all of the rest of the bytes representing the very # very last byte. # # All of which is enough to compute an amount of extra data that is required # to be safe. To avoid problems at the block level allocating 5 extra bytes # per 32767 bytes of data is sufficient. To avoid problems internal to a # block adding an extra 32767 bytes (the worst case uncompressed block size) # is sufficient, to ensure that in the worst case the decompressed data for # block will stop the byte before the compressed data for a block begins. # To avoid problems with the compressed data's meta information an extra 18 # bytes are needed. Leading to the formula: # # extra_bytes = (uncompressed_size >> 12) + 32768 + 18 # # Adding 8 bytes per 32K is a bit excessive but much easier to calculate. # Adding 32768 instead of 32767 just makes for round numbers. # # Above analysis is for decompressing gzip compressed kernel only. Up to # now 6 different decompressor are supported all together. And among them # xz stores data in chunks and has maximum chunk of 64K. Hence safety # margin should be updated to cover all decompressors so that we don't # need to deal with each of them separately. Please check # the description in lib/decompressor_xxx.c for specific information. # # extra_bytes = (uncompressed_size >> 12) + 65536 + 128 # # LZ4 is even worse: data that cannot be further compressed grows by 0.4%, # or one byte per 256 bytes. OTOH, we can safely get rid of the +128 as # the size-dependent part now grows so fast. # # extra_bytes = (uncompressed_size >> 8) + 65536 #define ZO_z_extra_bytes ((ZO_z_output_len >> 8) + 65536) #if ZO_z_output_len > ZO_z_input_len # define ZO_z_extract_offset (ZO_z_output_len + ZO_z_extra_bytes - \ ZO_z_input_len) #else # define ZO_z_extract_offset ZO_z_extra_bytes #endif /* * The extract_offset has to be bigger than ZO head section. Otherwise when * the head code is running to move ZO to the end of the buffer, it will * overwrite the head code itself. */ #if (ZO__ehead - ZO_startup_32) > ZO_z_extract_offset # define ZO_z_min_extract_offset ((ZO__ehead - ZO_startup_32 + 4095) & ~4095) #else # define ZO_z_min_extract_offset ((ZO_z_extract_offset + 4095) & ~4095) #endif #define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_min_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 handover_offset: .long 0 # Filled in by build.c # End of setup header ##################################################### .section ".entrytext", "ax" setup: # Force %es = %ds movw %ds, %ax movw %ax, %es cld 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 "Signature du systeme non trouvee...\n"