384 lines
11 KiB
ArmAsm
384 lines
11 KiB
ArmAsm
/*******************************************************************************/
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/* COS2000 - Compatible Operating System - LGPL v3 - Hordé Nicolas */
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/* */
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/* Modifié depuis header.S
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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*
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* Based on bootsect.S and setup.S
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* modified by more people than can be counted
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*
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* Rewritten as a common file by H. Peter Anvin (Apr 2007)
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*
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* BIG FAT NOTE: We're in real mode using 64k segments. Therefore segment
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* addresses must be multiplied by 16 to obtain their respective linear
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* addresses. To avoid confusion, linear addresses are written using leading
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* hex while segment addresses are written as segment:offset.
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*
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*/
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#include "voffset.h"
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#include "zoffset.h"
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#define __AC(X, Y) (X##Y)
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#define _AC(X, Y) __AC(X,Y)
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#define ROOT_RDONLY 1
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#define LOADED_HIGH 1
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#define SVGA_MODE 0
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#define CONFIG_PHYSICAL_ALIGN 0x100000
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#define MIN_KERNEL_ALIGN_LG2 4
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#define COMMAND_LINE_SIZE 512
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#define LOAD_PHYSICAL_ADDR 0x100000
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/* loadflags */
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#define LOADED_HIGH_FLAG (1<<0)
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#define KASLR_FLAG (1<<1)
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#define QUIET_FLAG (1<<5)
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#define KEEP_SEGMENTS (1<<6)
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#define CAN_USE_HEAP (1<<7)
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SEGBOOT = 0x07C0
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SEGSYS = 0x1000
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STACK_SIZE = 1024
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.code16
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.section ".bstext", "ax"
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.global bootsectstart
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bootsectstart:
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ljmp $SEGBOOT, $start2
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start2:
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movw %cs, %ax
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movw %ax, %ds
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movw %ax, %es
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movw %ax, %ss
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xorw %sp, %sp
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sti
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cld
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movw $msgtxt, %si
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msg:
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lodsb
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andb %al, %al
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jz dienow
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movb $0xe, %ah
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movw $7, %bx
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int $0x10
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jmp msg
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dienow:
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xorw %ax, %ax
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int $0x16
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int $0x19
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ljmp $0xf000,$0xfff0
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.section ".bsdata", "a"
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msgtxt:
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.ascii "Utilisez un chargeur de demarrage !\r\n<Pressez une touche pour redemarrer>\r\n"
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.byte 0
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.section ".header", "a"
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.globl sentinel
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sentinel: .byte 0xff, 0xff
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.globl hdr
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hdr:
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setup_sects: .byte 0 /* Filled in by build.c */
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root_flags: .word ROOT_RDONLY
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syssize: .long 0 /* Filled in by build.c */
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ram_size: .word 0 /* Obsolete */
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vid_mode: .word SVGA_MODE
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root_dev: .word 0 /* Filled in by build.c */
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boot_flag: .word 0xAA55
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# offset 512, entry point
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.globl _start
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_start:
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.byte 0xeb # short (2-byte) jump
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.byte setup-1f
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1:
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.ascii "HdrS" # header signature
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.word 0x020d # header version number (>= 0x0105) or else old loadlin-1.5 will fail)
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.globl realmode_swtch
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realmode_swtch: .word 0, 0 # default_switch, SETUPSEG
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start_sys_seg: .word SEGSYS # obsolete and meaningless, but just
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# in case something decided to "use" it
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.word kernel_version-512 # pointing to kernel version string
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# above section of header is compatible
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# with loadlin-1.5 (header v1.5). Don't
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# change it.
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type_of_loader: .byte 0 # 0 means ancient bootloader, newer
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# bootloaders know to change this.
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# See Documentation/x86/boot.txt for
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# assigned ids
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# flags, unused bits must be zero (RFU) bit within loadflags
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loadflags:
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.byte LOADED_HIGH # The kernel is to be loaded high
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setup_move_size: .word 0x8000 # size to move, when setup is not
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# loaded at 0x90000. We will move setup
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# to 0x90000 then just before jumping
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# into the kernel. However, only the
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# loader knows how much data behind
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# us also needs to be loaded.
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code32_start: # here loaders can put a different
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# start address for 32-bit code.
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.long LOAD_PHYSICAL_ADDR # 0x100000 = default for big kernel
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ramdisk_image: .long 0 # address of loaded ramdisk image
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# Here the loader puts the 32-bit
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# address where it loaded the image.
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# This only will be read by the kernel.
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ramdisk_size: .long 0 # its size in bytes
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bootsect_kludge:
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.long 0 # obsolete
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heap_end_ptr: .word _end+STACK_SIZE-512
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# (Header version 0x0201 or later)
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# space from here (exclusive) down to
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# end of setup code can be used by setup
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# for local heap purposes.
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ext_loader_ver:
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.byte 0 # Extended boot loader version
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ext_loader_type:
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.byte 0 # Extended boot loader type
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cmd_line_ptr: .long 0 # (Header version 0x0202 or later)
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# If nonzero, a 32-bit pointer
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# to the kernel command line.
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# The command line should be
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# located between the start of
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# setup and the end of low
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# memory (0xa0000), or it may
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# get overwritten before it
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# gets read. If this field is
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# used, there is no longer
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# anything magical about the
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# 0x90000 segment; the setup
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# can be located anywhere in
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# low memory 0x10000 or higher.
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initrd_addr_max: .long 0x7fffffff
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# (Header version 0x0203 or later)
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# The highest safe address for
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# the contents of an initrd
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# The current kernel allows up to 4 GB,
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# but leave it at 2 GB to avoid
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# possible bootloader bugs.
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kernel_alignment: .long CONFIG_PHYSICAL_ALIGN #physical addr alignment
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#required for protected mode
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#kernel
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relocatable_kernel: .byte 0
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min_alignment: .byte MIN_KERNEL_ALIGN_LG2 # minimum alignment
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xloadflags:
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.word 0
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cmdline_size: .long COMMAND_LINE_SIZE-1 #length of the command line,
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#added with boot protocol
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#version 2.06
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hardware_subarch: .long 0 # subarchitecture, added with 2.07
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# default to 0 for normal x86 PC
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hardware_subarch_data: .quad 0
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payload_offset: .long ZO_input_data
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payload_length: .long ZO_z_input_len
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setup_data: .quad 0 # 64-bit physical pointer to
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# single linked list of
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# struct setup_data
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pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr
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#
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# Getting to provably safe in-place decompression is hard. Worst case
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# behaviours need to be analyzed. Here let's take the decompression of
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# a gzip-compressed kernel as example, to illustrate it:
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#
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# The file layout of gzip compressed kernel is:
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#
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# magic[2]
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# method[1]
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# flags[1]
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# timestamp[4]
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# extraflags[1]
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# os[1]
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# compressed data blocks[N]
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# crc[4] orig_len[4]
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#
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# ... resulting in +18 bytes overhead of uncompressed data.
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#
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# (For more information, please refer to RFC 1951 and RFC 1952.)
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#
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# Files divided into blocks
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# 1 bit (last block flag)
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# 2 bits (block type)
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#
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# 1 block occurs every 32K -1 bytes or when there 50% compression
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# has been achieved. The smallest block type encoding is always used.
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#
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# stored:
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# 32 bits length in bytes.
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#
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# fixed:
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# magic fixed tree.
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# symbols.
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#
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# dynamic:
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# dynamic tree encoding.
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# symbols.
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#
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#
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# The buffer for decompression in place is the length of the uncompressed
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# data, plus a small amount extra to keep the algorithm safe. The
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# compressed data is placed at the end of the buffer. The output pointer
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# is placed at the start of the buffer and the input pointer is placed
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# where the compressed data starts. Problems will occur when the output
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# pointer overruns the input pointer.
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#
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# The output pointer can only overrun the input pointer if the input
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# pointer is moving faster than the output pointer. A condition only
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# triggered by data whose compressed form is larger than the uncompressed
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# form.
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#
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# The worst case at the block level is a growth of the compressed data
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# of 5 bytes per 32767 bytes.
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#
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# The worst case internal to a compressed block is very hard to figure.
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# The worst case can at least be bounded by having one bit that represents
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# 32764 bytes and then all of the rest of the bytes representing the very
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# very last byte.
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#
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# All of which is enough to compute an amount of extra data that is required
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# to be safe. To avoid problems at the block level allocating 5 extra bytes
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# per 32767 bytes of data is sufficient. To avoid problems internal to a
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# block adding an extra 32767 bytes (the worst case uncompressed block size)
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# is sufficient, to ensure that in the worst case the decompressed data for
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# block will stop the byte before the compressed data for a block begins.
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# To avoid problems with the compressed data's meta information an extra 18
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# bytes are needed. Leading to the formula:
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#
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# extra_bytes = (uncompressed_size >> 12) + 32768 + 18
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#
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# Adding 8 bytes per 32K is a bit excessive but much easier to calculate.
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# Adding 32768 instead of 32767 just makes for round numbers.
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#
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# Above analysis is for decompressing gzip compressed kernel only. Up to
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# now 6 different decompressor are supported all together. And among them
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# xz stores data in chunks and has maximum chunk of 64K. Hence safety
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# margin should be updated to cover all decompressors so that we don't
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# need to deal with each of them separately. Please check
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# the description in lib/decompressor_xxx.c for specific information.
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#
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# extra_bytes = (uncompressed_size >> 12) + 65536 + 128
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#
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# LZ4 is even worse: data that cannot be further compressed grows by 0.4%,
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# or one byte per 256 bytes. OTOH, we can safely get rid of the +128 as
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# the size-dependent part now grows so fast.
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#
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# extra_bytes = (uncompressed_size >> 8) + 65536
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#define ZO_z_extra_bytes ((ZO_z_output_len >> 8) + 65536)
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#if ZO_z_output_len > ZO_z_input_len
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# define ZO_z_extract_offset (ZO_z_output_len + ZO_z_extra_bytes - \
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ZO_z_input_len)
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#else
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# define ZO_z_extract_offset ZO_z_extra_bytes
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#endif
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/*
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* The extract_offset has to be bigger than ZO head section. Otherwise when
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* the head code is running to move ZO to the end of the buffer, it will
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* overwrite the head code itself.
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*/
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#if (ZO__ehead - ZO_startup_32) > ZO_z_extract_offset
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# define ZO_z_min_extract_offset ((ZO__ehead - ZO_startup_32 + 4095) & ~4095)
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#else
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# define ZO_z_min_extract_offset ((ZO_z_extract_offset + 4095) & ~4095)
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#endif
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#define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_min_extract_offset)
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#define VO_INIT_SIZE (VO__end - VO__text)
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#if ZO_INIT_SIZE > VO_INIT_SIZE
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# define INIT_SIZE ZO_INIT_SIZE
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#else
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# define INIT_SIZE VO_INIT_SIZE
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#endif
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init_size: .long INIT_SIZE # kernel initialization size
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handover_offset: .long 0 # Filled in by build.c
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# End of setup header #####################################################
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.section ".entrytext", "ax"
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setup:
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# Force %es = %ds
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movw %ds, %ax
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movw %ax, %es
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cld
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movw %ss, %dx
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cmpw %ax, %dx # %ds == %ss?
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movw %sp, %dx
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je 2f # -> assume %sp is reasonably set
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# Invalid %ss, make up a new stack
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movw $_end, %dx
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testb $CAN_USE_HEAP, loadflags
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jz 1f
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movw heap_end_ptr, %dx
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1: addw $STACK_SIZE, %dx
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jnc 2f
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xorw %dx, %dx # Prevent wraparound
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2: # Now %dx should point to the end of our stack space
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andw $~3, %dx # dword align (might as well...)
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jnz 3f
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movw $0xfffc, %dx # Make sure we're not zero
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3: movw %ax, %ss
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movzwl %dx, %esp # Clear upper half of %esp
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sti # Now we should have a working stack
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# We will have entered with %cs = %ds+0x20, normalize %cs so
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# it is on par with the other segments.
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pushw %ds
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pushw $6f
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lretw
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6:
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# Check signature at end of setup
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cmpl $0x5a5aaa55, setup_sig
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jne setup_bad
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# Zero the bss
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movw $__bss_start, %di
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movw $_end+3, %cx
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xorl %eax, %eax
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subw %di, %cx
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shrw $2, %cx
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rep; stosl
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# Jump to C code (should not return)
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calll main
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# Setup corrupt somehow...
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setup_bad:
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movl $setup_corrupt, %eax
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calll showstr
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# Fall through...
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.globl die
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.type die, @function
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die:
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hlt
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jmp die
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.size die, .-die
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.section ".initdata", "a"
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setup_corrupt:
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.byte 7
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.string "Signature du systeme non trouvee...\n"
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