80x86 PC BIOS PXE Boot Loader

80x86 PC BIOS PXE Boot Loader
File: 80x86/sys_src/p1/pc_bios/bootpxe/0index.asm

Copyright © Brendan Trotter 2008

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Overview

This index file determines the layout of all other source files in memory. The final binary is used to boot the OS from a network card via. PXE.

Like all boot loaders designed for the PC BIOS, this boot loader must comply with the Common PC BIOS Module Transition State Specification.

Included System Files

The following line/s include standard "include" files into the binary.

22: ;Standard include files
23:
24: %include "asm.inc"
25: %include "kernel/log.inc"
26: %include "kernel/a20.inc"
27: %include "kernel/pasm.inc"
28: %include "ff/header.inc"
29: %include "ff/frl.inc"
30:
31:
32: ;PXE boot loader include files
33:
34: %include "options.inc"
35: %include "pxe.inc"

Assembler Setup

Here we just tell the assembler what address the code starts at, what mode the CPU is expected to be operating in and which instructions to accept.

Note: This code starts as "8086 compatible", then checks if the CPU meets the operating system's minimum requirements. After this check we tell the assembler to allow the full "80486" instruction set.

48:       ORG 0x7C00
49:
50:       BITS 16
51:       CPU 8086
52:
53: BOOTLOADER_START:
54:       section .bss
55: BSS_START:
56:       section .text

Start of Binary and Entry Point

This is the beginning of the binary, which is also the entry point. When PXE starts the boot loader everything should be considered undefined, except for the registers shown below.

A far jump is used deliberately to set CS to a known value (even though the PXE specification says that PXE should use 0x0000:0x7C00 and not 0x07C0:0x0000).

68: ;Input
69: ; es:bx     Address of the PXENV+ structure (obsolete)
70: ; ss:sp+4   Address of the !PXE structure
71:
72:       jmp 0x0000:START

Source Code

78: %include "data.asm"
79: %include "init.asm"
80: %include "abort.asm"
81: %include "video/init.asm"
82: %include "video/print.asm"
83: %include "cpu.asm"
84:
85: CPU 486
86:
87: %include "gatea20.asm"
88: %include "goflat.asm"
89: %include "pxeapi.asm"
90: %include "unload.asm"
91: %include "progress.asm"
92: %include "log/init.asm"
93: %include "log/movelog.asm"
94: %include "log/addchar.asm"
95: %include "log/addstrng.asm"
96: %include "log/addhex.asm"
97: %include "log/addip.asm"
98: %include "log/addmac.asm"
99: %include "log/adddec.asm"
100: %include "pasm/init.asm"
101: %include "pasm/addentry.asm"
102: %include "pasm/probe.asm"
103: %include "pasm/cmos.asm"
104: %include "pasm/88.asm"
105: %include "pasm/da88.asm"
106: %include "pasm/8a.asm"
107: %include "pasm/c7.asm"
108: %include "pasm/e801.asm"
109: ;%include "pasm/e881.asm" ;Disabled due to buggy BIOSs (see note in "pasm/init.asm")
110: %include "pasm/e820.asm"
111: %include "pasm/e820acpi.asm"
112: %include "pasm/showpasm.asm"
113: %include "pasm/findtop.asm"
114: %include "pasm/movepasm.asm"
115: %include "pasm/foreach.asm"
116: %include "nff/precheck.asm"
117: %include "nff/crc.asm"
118: %include "frl/init.asm"
119: %include "frl/check.asm"
120: %include "frl/movefrl.asm"
121: %include "frl/bitmap.asm"
122: %include "frl/chcktrust.asm"
123: %include "frl/clean.asm"
124: %include "mem/init.asm"
125: %include "mem/alloc.asm"
126: %include "mem/free.asm"
127: %include "mem/test.asm"
128: %include "mem/show.asm"
129: %include "file/start.asm"
130: %include "file/end.asm"
131: %include "commonpc/init.asm"
132: %include "commonpc/start.asm"
133: %include "script/init.asm"
134: %include "image/init.asm"
135: %include "bcat/init.asm"
136: %include "bcat/addentry.asm"
137: %include "bcat/finalize.asm"

The End

Here we define a few labels that are used later.

145:       align 4
146: BOOTLOADER_END:
147:       section .bss
148:       alignb 4
149: BSS_END:
150:
151: %if (BSS_END-BSS_START + BOOTLOADER_END-BOOTLOADER_START) > 0xFFFF
152: %error Maximum TFTP pack size setting (in 'options.inc') is too large!
153: %endif

Generated on Sun Aug 16 02:07:23 2009