xref: /freebsd/stand/i386/btx/btxldr/btxldr.S (revision 7fdf597e96a02165cfe22ff357b857d5fa15ed8a)
1/*
2 * Copyright (c) 1998 Robert Nordier
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms are freely
6 * permitted provided that the above copyright notice and this
7 * paragraph and the following disclaimer are duplicated in all
8 * such forms.
9 *
10 * This software is provided "AS IS" and without any express or
11 * implied warranties, including, without limitation, the implied
12 * warranties of merchantability and fitness for a particular
13 * purpose.
14 */
15
16#include <bootargs.h>
17
18#define	RBX_MUTE	0x10	/* -m */
19#define	OPT_SET(opt)	(1 << (opt))
20
21/*
22 * Prototype BTX loader program, written in a couple of hours.  The
23 * real thing should probably be more flexible, and in C.
24 */
25
26/*
27 * Memory locations.
28 */
29		.set MEM_STUB,0x600		# Real mode stub
30		.set MEM_ESP,0x1000		# New stack pointer
31		.set MEM_TBL,0x5000		# BTX page tables
32		.set MEM_ENTRY,0x9010		# BTX entry point
33		.set MEM_DATA,start+0x1000	# Data segment
34/*
35 * Segment selectors.
36 */
37		.set SEL_SCODE,0x8		# 4GB code
38		.set SEL_SDATA,0x10		# 4GB data
39		.set SEL_RCODE,0x18		# 64K code
40		.set SEL_RDATA,0x20		# 64K data
41/*
42 * Paging constants.
43 */
44		.set PAG_SIZ,0x1000		# Page size
45		.set PAG_ENT,0x4		# Page entry size
46/*
47 * Screen constants.
48 */
49		.set SCR_MAT,0x7		# Mode/attribute
50		.set SCR_COL,0x50		# Columns per row
51		.set SCR_ROW,0x19		# Rows per screen
52/*
53 * BIOS Data Area locations.
54 */
55		.set BDA_MEM,0x413		# Free memory
56		.set BDA_SCR,0x449		# Video mode
57		.set BDA_POS,0x450		# Cursor position
58/*
59 * Required by aout gas inadequacy.
60 */
61		.set SIZ_STUB,0x1a		# Size of stub
62/*
63 * We expect to be loaded by boot2 at the origin defined in ./Makefile.
64 */
65		.globl start
66/*
67 * BTX program loader for ELF clients.
68 */
69start:		cld				# String ops inc
70		testl $OPT_SET(RBX_MUTE), 4(%esp) # Check first argument
71		setnz muted			#  for RBX_MUTE, set flag
72		movl $m_logo,%esi		# Identify
73		call putstr			#  ourselves
74		movzwl BDA_MEM,%eax		# Get base memory
75		shll $0xa,%eax			#  in bytes
76		movl %eax,%ebp			# Base of user stack
77#ifdef BTXLDR_VERBOSE
78		movl $m_mem,%esi		# Display
79		call hexout			#  amount of
80		call putstr			#  base memory
81#endif
82		lgdt gdtdesc			# Load new GDT
83/*
84 * Relocate caller's arguments.
85 */
86#ifdef BTXLDR_VERBOSE
87		movl $m_esp,%esi		# Display
88		movl %esp,%eax			#  caller
89		call hexout			#  stack
90		call putstr			#  pointer
91		movl $m_args,%esi		# Format string
92		leal 0x4(%esp),%ebx		# First argument
93		movl $0x6,%ecx			# Count
94start.1:	movl (%ebx),%eax		# Get argument and
95		addl $0x4,%ebx			#  bump pointer
96		call hexout			# Display it
97		loop start.1			# Till done
98		call putstr			# End message
99#endif
100		movl BA_BOOTINFO+4(%esp),%esi	# Source: bootinfo
101		cmpl $0x0, %esi			# If the bootinfo pointer
102		je start_null_bi		#  is null, don't copy it
103		movl BI_SIZE(%esi),%ecx 	# Allocate space
104		subl %ecx,%ebp			#  for bootinfo
105		movl %ebp,%edi			# Destination
106		rep				# Copy
107		movsb				#  it
108		movl %ebp,BA_BOOTINFO+4(%esp)	# Update pointer
109		movl %edi,%ebp			# Restore base pointer
110#ifdef BTXLDR_VERBOSE
111		movl $m_rel_bi,%esi		# Display
112		movl %ebp,%eax			#  bootinfo
113		call hexout			#  relocation
114		call putstr			#  message
115#endif
116start_null_bi:	movl $BOOTARGS_SIZE,%ecx 	# Fixed size of arguments
117		testl $KARGS_FLAGS_EXTARG, BA_BOOTFLAGS+4(%esp) # Check for extra data
118		jz start_fixed			# Skip if the flag is not set
119		addl BOOTARGS_SIZE+4(%esp),%ecx	# Add size of variable args
120start_fixed:	subl $ARGOFF,%ebp		# Place args at fixed offset
121		leal 0x4(%esp),%esi		# Source
122		movl %ebp,%edi			# Destination
123		rep				# Copy
124		movsb				#  them
125#ifdef BTXLDR_VERBOSE
126		movl $m_rel_args,%esi		# Display
127		movl %ebp,%eax			#  argument
128		call hexout			#  relocation
129		call putstr			#  message
130#endif
131/*
132 * Set up BTX kernel.
133 */
134		movl $MEM_ESP,%esp		# Set up new stack
135		movl $MEM_DATA,%ebx		# Data segment
136		movl $m_vers,%esi		# Display BTX
137		call putstr			#  version message
138		movb 0x5(%ebx),%al		# Get major version
139		addb $'0',%al			# Display
140		call putchr			#  it
141		movb $'.',%al			# And a
142		call putchr			#  dot
143		movb 0x6(%ebx),%al		# Get minor
144		xorb %ah,%ah			#  version
145		movb $0xa,%dl			# Divide
146		divb %dl,%al			#  by 10
147		addb $'0',%al			# Display
148		call putchr			#  tens
149		movb %ah,%al			# Get units
150		addb $'0',%al			# Display
151		call putchr			#  units
152		call putstr			# End message
153		movl %ebx,%esi			# BTX image
154		movzwl 0x8(%ebx),%edi		# Compute
155		orl $PAG_SIZ/PAG_ENT-1,%edi	#  the
156		incl %edi			#  BTX
157		shll $0x2,%edi			#  load
158		addl $MEM_TBL,%edi		#  address
159		pushl %edi			# Save load address
160		movzwl 0xa(%ebx),%ecx		# Image size
161#ifdef BTXLDR_VERBOSE
162		pushl %ecx			# Save image size
163#endif
164		rep				# Relocate
165		movsb				#  BTX
166		movl %esi,%ebx			# Keep place
167#ifdef BTXLDR_VERBOSE
168		movl $m_rel_btx,%esi		# Restore
169		popl %eax			#  parameters
170		call hexout			#  and
171#endif
172		popl %ebp			#  display
173#ifdef BTXLDR_VERBOSE
174		movl %ebp,%eax			#  the
175		call hexout			#  relocation
176		call putstr			#  message
177#endif
178		addl $PAG_SIZ,%ebp		# Display
179#ifdef BTXLDR_VERBOSE
180		movl $m_base,%esi		#  the
181		movl %ebp,%eax			#  user
182		call hexout			#  base
183		call putstr			#  address
184#endif
185/*
186 * Set up ELF-format client program.
187 */
188		cmpl $0x464c457f,(%ebx) 	# ELF magic number?
189		je start.3			# Yes
190		movl $e_fmt,%esi		# Display error
191		call putstr			#  message
192start.2:	jmp start.2			# Hang
193start.3:
194#ifdef BTXLDR_VERBOSE
195		movl $m_elf,%esi		# Display ELF
196		call putstr			#  message
197		movl $m_segs,%esi		# Format string
198#endif
199		movl 0x1c(%ebx),%edx		# Get e_phoff
200		addl %ebx,%edx			# To pointer
201		movzwl 0x2c(%ebx),%ecx		# Get e_phnum
202start.4:	cmpl $0x1,(%edx)		# Is p_type PT_LOAD?
203		jne start.6			# No
204#ifdef BTXLDR_VERBOSE
205		movl 0x4(%edx),%eax		# Display
206		call hexout			#  p_offset
207		movl 0x8(%edx),%eax		# Display
208		call hexout			#  p_vaddr
209		movl 0x10(%edx),%eax		# Display
210		call hexout			#  p_filesz
211		movl 0x14(%edx),%eax		# Display
212		call hexout			#  p_memsz
213		call putstr			# End message
214#endif
215		pushl %esi			# Save
216		pushl %ecx			#  working registers
217		movl 0x4(%edx),%esi		# Get p_offset
218		addl %ebx,%esi			#  as pointer
219		movl 0x8(%edx),%edi		# Get p_vaddr
220		addl %ebp,%edi			#  as pointer
221		movl 0x10(%edx),%ecx		# Get p_filesz
222		rep				# Set up
223		movsb				#  segment
224		movl 0x14(%edx),%ecx		# Any bytes
225		subl 0x10(%edx),%ecx		#  to zero?
226		jz start.5			# No
227		xorb %al,%al			# Then
228		rep				#  zero
229		stosb				#  them
230start.5:	popl %ecx			# Restore
231		popl %esi			#  registers
232start.6:	addl $0x20,%edx 		# To next entry
233		loop start.4			# Till done
234#ifdef BTXLDR_VERBOSE
235		movl $m_done,%esi		# Display done
236		call putstr			#  message
237#endif
238		movl $start.8,%esi		# Real mode stub
239		movl $MEM_STUB,%edi		# Destination
240		movl $start.9-start.8,%ecx	# Size
241		rep				# Relocate
242		movsb				#  it
243		ljmp $SEL_RCODE,$MEM_STUB	# To 16-bit code
244		.code16
245start.8:	xorw %ax,%ax			# Data
246		movb $SEL_RDATA,%al		#  selector
247		movw %ax,%ss			# Reload SS
248		movw %ax,%ds			# Reset
249		movw %ax,%es			#  other
250		movw %ax,%fs			#  segment
251		movw %ax,%gs			#  limits
252		movl %cr0,%eax			# Switch to
253		decw %ax			#  real
254		movl %eax,%cr0			#  mode
255		ljmp $0,$MEM_ENTRY		# Jump to BTX entry point
256start.9:
257		.code32
258/*
259 * Output message [ESI] followed by EAX in hex.
260 */
261hexout: 	pushl %eax			# Save
262		call putstr			# Display message
263		popl %eax			# Restore
264		pushl %esi			# Save
265		pushl %edi			#  caller's
266		movl $buf,%edi			# Buffer
267		pushl %edi			# Save
268		call hex32			# To hex
269		xorb %al,%al			# Terminate
270		stosb				#  string
271		popl %esi			# Restore
272hexout.1:	lodsb				# Get a char
273		cmpb $'0',%al			# Leading zero?
274		je hexout.1			# Yes
275		testb %al,%al			# End of string?
276		jne hexout.2			# No
277		decl %esi			# Undo
278hexout.2:	decl %esi			# Adjust for inc
279		call putstr			# Display hex
280		popl %edi			# Restore
281		popl %esi			#  caller's
282		ret				# To caller
283/*
284 * Output zero-terminated string [ESI] to the console.
285 */
286putstr.0:	call putchr			# Output char
287putstr: 	lodsb				# Load char
288		testb %al,%al			# End of string?
289		jne putstr.0			# No
290		ret				# To caller
291/*
292 * Output character AL to the console.
293 */
294putchr:		testb $1,muted			# Check muted
295		jnz putchr.5			#  do a nop
296		pusha				# Save
297		xorl %ecx,%ecx			# Zero for loops
298		movb $SCR_MAT,%ah		# Mode/attribute
299		movl $BDA_POS,%ebx		# BDA pointer
300		movw (%ebx),%dx 		# Cursor position
301		movl $0xb8000,%edi		# Regen buffer (color)
302		cmpb %ah,BDA_SCR-BDA_POS(%ebx)	# Mono mode?
303		jne putchr.1			# No
304		xorw %di,%di			# Regen buffer (mono)
305putchr.1:	cmpb $0xa,%al			# New line?
306		je putchr.2			# Yes
307		xchgl %eax,%ecx 		# Save char
308		movb $SCR_COL,%al		# Columns per row
309		mulb %dh			#  * row position
310		addb %dl,%al			#  + column
311		adcb $0x0,%ah			#  position
312		shll %eax			#  * 2
313		xchgl %eax,%ecx 		# Swap char, offset
314		movw %ax,(%edi,%ecx,1)		# Write attr:char
315		incl %edx			# Bump cursor
316		cmpb $SCR_COL,%dl		# Beyond row?
317		jb putchr.3			# No
318putchr.2:	xorb %dl,%dl			# Zero column
319		incb %dh			# Bump row
320putchr.3:	cmpb $SCR_ROW,%dh		# Beyond screen?
321		jb putchr.4			# No
322		leal 2*SCR_COL(%edi),%esi	# New top line
323		movw $(SCR_ROW-1)*SCR_COL/2,%cx # Words to move
324		rep				# Scroll
325		movsl				#  screen
326		movb $' ',%al			# Space
327		movb $SCR_COL,%cl		# Columns to clear
328		rep				# Clear
329		stosw				#  line
330		movb $SCR_ROW-1,%dh		# Bottom line
331putchr.4:	movw %dx,(%ebx) 		# Update position
332		popa				# Restore
333putchr.5:	ret				# To caller
334/*
335 * Convert EAX, AX, or AL to hex, saving the result to [EDI].
336 */
337hex32:		pushl %eax			# Save
338		shrl $0x10,%eax 		# Do upper
339		call hex16			#  16
340		popl %eax			# Restore
341hex16:		call hex16.1			# Do upper 8
342hex16.1:	xchgb %ah,%al			# Save/restore
343hex8:		pushl %eax			# Save
344		shrb $0x4,%al			# Do upper
345		call hex8.1			#  4
346		popl %eax			# Restore
347hex8.1: 	andb $0xf,%al			# Get lower 4
348		cmpb $0xa,%al			# Convert
349		sbbb $0x69,%al			#  to hex
350		das				#  digit
351		orb $0x20,%al			# To lower case
352		stosb				# Save char
353		ret				# (Recursive)
354
355		.data
356		.p2align 4
357/*
358 * Global descriptor table.
359 */
360gdt:		.word 0x0,0x0,0x0,0x0		# Null entry
361		.word 0xffff,0x0,0x9a00,0xcf	# SEL_SCODE
362		.word 0xffff,0x0,0x9200,0xcf	# SEL_SDATA
363		.word 0xffff,0x0,0x9a00,0x0	# SEL_RCODE
364		.word 0xffff,0x0,0x9200,0x0	# SEL_RDATA
365gdt.1:
366gdtdesc:	.word gdt.1-gdt-1		# Limit
367		.long gdt			# Base
368/*
369 * Messages.
370 */
371m_logo: 	.asciz " \nBTX loader 1.00  "
372m_vers: 	.asciz "BTX version is \0\n"
373e_fmt:		.asciz "Error: Client format not supported\n"
374#ifdef BTXLDR_VERBOSE
375m_mem:		.asciz "Starting in protected mode (base mem=\0)\n"
376m_esp:		.asciz "Arguments passed (esp=\0):\n"
377m_args: 	.asciz "<howto="
378		.asciz " bootdev="
379		.asciz " junk="
380		.asciz " "
381		.asciz " "
382		.asciz " bootinfo=\0>\n"
383m_rel_bi:	.asciz "Relocated bootinfo (size=48) to \0\n"
384m_rel_args:	.asciz "Relocated arguments (size=18) to \0\n"
385m_rel_btx:	.asciz "Relocated kernel (size=\0) to \0\n"
386m_base: 	.asciz "Client base address is \0\n"
387m_elf:		.asciz "Client format is ELF\n"
388m_segs: 	.asciz "text segment: offset="
389		.asciz " vaddr="
390		.asciz " filesz="
391		.asciz " memsz=\0\n"
392		.asciz "data segment: offset="
393		.asciz " vaddr="
394		.asciz " filesz="
395		.asciz " memsz=\0\n"
396m_done: 	.asciz "Loading complete\n"
397#endif
398
399/*
400 * Flags
401 */
402muted:		.byte 0x0
403
404/*
405 * Uninitialized data area.
406 */
407buf:						# Scratch buffer
408