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698f86f25a
mechanism has changed anyway, and so must be rewritten, but at least doing this makes the output of "make symcheck" more legible.
142 lines
3.8 KiB
ArmAsm
142 lines
3.8 KiB
ArmAsm
/*
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Copyright (C) 2000, Entity Cyber, Inc.
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Authors: Gary Byers (gb@thinguin.org)
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Marty Connor (mdc@thinguin.org)
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This software may be used and distributed according to the terms
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of the GNU Public License (GPL), incorporated herein by reference.
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Description:
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This is just a little bit of code and data that can get prepended
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to an Etherboot ROM image in order to allow LILO to load the
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result as if it were a Linux kernel image.
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A real Linux kernel image consists of a one-sector boot loader
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(to load the image from a floppy disk), followed a few sectors
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of setup code, followed by the kernel code itself. There's
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a table in the first sector (starting at offset 497) that indicates
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how many sectors of setup code follow the first sector and which
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contains some other parameters that aren't interesting in this
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case.
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When LILO loads the sectors that comprise a kernel image, it doesn't
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execute the code in the first sector (since that code would try to
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load the image from a floppy disk.) The code in the first sector
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below doesn't expect to get executed (and prints an error message
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if it ever -is- executed.) LILO's only interested in knowing the
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number of setup sectors advertised in the table (at offset 497 in
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the first sector.)
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Etherboot doesn't require much in the way of setup code.
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Historically, the Linux kernel required at least 4 sectors of
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setup code. Current versions of LILO look at the byte at
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offset 497 in the first sector to indicate how many sectors
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of setup code are contained in the image.
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*/
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#define SETUPSECS 4 /* Minimal nr of setup-sectors */
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#define PREFIXSIZE ((SETUPSECS+1)*512)
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#define PREFIXPGH (PREFIXSIZE / 16 )
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#define BOOTSEG 0x07C0 /* original address of boot-sector */
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#define INITSEG 0x9000 /* we move boot here - out of the way */
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#define SETUPSEG 0x9020 /* setup starts here */
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#define SYSSEG 0x1000 /* system loaded at 0x10000 (65536). */
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.text
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.code16
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.arch i386
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.org 0
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.section ".prefix", "ax", @progbits
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_prefix:
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/*
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This is a minimal boot sector. If anyone tries to execute it (e.g., if
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a .lilo file is dd'ed to a floppy), print an error message.
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*/
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bootsector:
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jmp $BOOTSEG, $go - _prefix /* reload cs:ip to match relocation addr */
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go:
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movw $0x2000, %di /* 0x2000 is arbitrary value >= length
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of bootsect + room for stack */
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movw $BOOTSEG, %ax
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movw %ax,%ds
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movw %ax,%es
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cli
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movw %ax, %ss /* put stack at BOOTSEG:0x2000. */
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movw %di,%sp
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sti
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movw $why_end-why, %cx
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movw $why - _prefix, %si
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movw $0x0007, %bx /* page 0, attribute 7 (normal) */
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movb $0x0e, %ah /* write char, tty mode */
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prloop:
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lodsb
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int $0x10
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loop prloop
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freeze: jmp freeze
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why: .ascii "This image cannot be loaded from a floppy disk.\r\n"
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why_end:
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.org 497
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setup_sects:
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.byte SETUPSECS
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root_flags:
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.word 0
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syssize:
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.word _verbatim_size_pgh - PREFIXPGH
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swap_dev:
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.word 0
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ram_size:
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.word 0
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vid_mode:
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.word 0
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root_dev:
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.word 0
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boot_flag:
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.word 0xAA55
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/*
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We're now at the beginning of the second sector of the image -
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where the setup code goes.
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We don't need to do too much setup for Etherboot.
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This code gets loaded at SETUPSEG:0. It wants to start
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executing the Etherboot image that's loaded at SYSSEG:0 and
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whose entry point is SYSSEG:0.
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*/
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setup_code:
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pushl $0 /* No parameters to preserve for exit path */
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pushw $0 /* Use prefix exit path mechanism */
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/* Etherboot expects to be contiguous in memory once loaded.
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* LILO doesn't do this, but since we don't need any
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* information that's left in the prefix, it doesn't matter:
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* we just have to ensure that %cs:0000 is where the start of
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* the Etherboot image *would* be.
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*/
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ljmp $(SYSSEG-(PREFIXSIZE/16)), $_start
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.section ".text16", "ax", @progbits
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prefix_exit:
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int $0x19 /* should try to boot machine */
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prefix_exit_end:
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.previous
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.org (PREFIXSIZE-1)
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.byte 0
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prefix_end:
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/*
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That's about it.
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*/
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