xref: /openbmc/linux/arch/x86/boot/header.S (revision 4da722ca)
1/*
2 *	header.S
3 *
4 *	Copyright (C) 1991, 1992 Linus Torvalds
5 *
6 *	Based on bootsect.S and setup.S
7 *	modified by more people than can be counted
8 *
9 *	Rewritten as a common file by H. Peter Anvin (Apr 2007)
10 *
11 * BIG FAT NOTE: We're in real mode using 64k segments.  Therefore segment
12 * addresses must be multiplied by 16 to obtain their respective linear
13 * addresses. To avoid confusion, linear addresses are written using leading
14 * hex while segment addresses are written as segment:offset.
15 *
16 */
17
18#include <asm/segment.h>
19#include <generated/utsrelease.h>
20#include <asm/boot.h>
21#include <asm/page_types.h>
22#include <asm/setup.h>
23#include <asm/bootparam.h>
24#include "boot.h"
25#include "voffset.h"
26#include "zoffset.h"
27
28BOOTSEG		= 0x07C0		/* original address of boot-sector */
29SYSSEG		= 0x1000		/* historical load address >> 4 */
30
31#ifndef SVGA_MODE
32#define SVGA_MODE ASK_VGA
33#endif
34
35#ifndef ROOT_RDONLY
36#define ROOT_RDONLY 1
37#endif
38
39	.code16
40	.section ".bstext", "ax"
41
42	.global bootsect_start
43bootsect_start:
44#ifdef CONFIG_EFI_STUB
45	# "MZ", MS-DOS header
46	.byte 0x4d
47	.byte 0x5a
48#endif
49
50	# Normalize the start address
51	ljmp	$BOOTSEG, $start2
52
53start2:
54	movw	%cs, %ax
55	movw	%ax, %ds
56	movw	%ax, %es
57	movw	%ax, %ss
58	xorw	%sp, %sp
59	sti
60	cld
61
62	movw	$bugger_off_msg, %si
63
64msg_loop:
65	lodsb
66	andb	%al, %al
67	jz	bs_die
68	movb	$0xe, %ah
69	movw	$7, %bx
70	int	$0x10
71	jmp	msg_loop
72
73bs_die:
74	# Allow the user to press a key, then reboot
75	xorw	%ax, %ax
76	int	$0x16
77	int	$0x19
78
79	# int 0x19 should never return.  In case it does anyway,
80	# invoke the BIOS reset code...
81	ljmp	$0xf000,$0xfff0
82
83#ifdef CONFIG_EFI_STUB
84	.org	0x3c
85	#
86	# Offset to the PE header.
87	#
88	.long	pe_header
89#endif /* CONFIG_EFI_STUB */
90
91	.section ".bsdata", "a"
92bugger_off_msg:
93	.ascii	"Use a boot loader.\r\n"
94	.ascii	"\n"
95	.ascii	"Remove disk and press any key to reboot...\r\n"
96	.byte	0
97
98#ifdef CONFIG_EFI_STUB
99pe_header:
100	.ascii	"PE"
101	.word 	0
102
103coff_header:
104#ifdef CONFIG_X86_32
105	.word	0x14c				# i386
106#else
107	.word	0x8664				# x86-64
108#endif
109	.word	4				# nr_sections
110	.long	0 				# TimeDateStamp
111	.long	0				# PointerToSymbolTable
112	.long	1				# NumberOfSymbols
113	.word	section_table - optional_header	# SizeOfOptionalHeader
114#ifdef CONFIG_X86_32
115	.word	0x306				# Characteristics.
116						# IMAGE_FILE_32BIT_MACHINE |
117						# IMAGE_FILE_DEBUG_STRIPPED |
118						# IMAGE_FILE_EXECUTABLE_IMAGE |
119						# IMAGE_FILE_LINE_NUMS_STRIPPED
120#else
121	.word	0x206				# Characteristics
122						# IMAGE_FILE_DEBUG_STRIPPED |
123						# IMAGE_FILE_EXECUTABLE_IMAGE |
124						# IMAGE_FILE_LINE_NUMS_STRIPPED
125#endif
126
127optional_header:
128#ifdef CONFIG_X86_32
129	.word	0x10b				# PE32 format
130#else
131	.word	0x20b 				# PE32+ format
132#endif
133	.byte	0x02				# MajorLinkerVersion
134	.byte	0x14				# MinorLinkerVersion
135
136	# Filled in by build.c
137	.long	0				# SizeOfCode
138
139	.long	0				# SizeOfInitializedData
140	.long	0				# SizeOfUninitializedData
141
142	# Filled in by build.c
143	.long	0x0000				# AddressOfEntryPoint
144
145	.long	0x0200				# BaseOfCode
146#ifdef CONFIG_X86_32
147	.long	0				# data
148#endif
149
150extra_header_fields:
151#ifdef CONFIG_X86_32
152	.long	0				# ImageBase
153#else
154	.quad	0				# ImageBase
155#endif
156	.long	0x20				# SectionAlignment
157	.long	0x20				# FileAlignment
158	.word	0				# MajorOperatingSystemVersion
159	.word	0				# MinorOperatingSystemVersion
160	.word	0				# MajorImageVersion
161	.word	0				# MinorImageVersion
162	.word	0				# MajorSubsystemVersion
163	.word	0				# MinorSubsystemVersion
164	.long	0				# Win32VersionValue
165
166	#
167	# The size of the bzImage is written in tools/build.c
168	#
169	.long	0				# SizeOfImage
170
171	.long	0x200				# SizeOfHeaders
172	.long	0				# CheckSum
173	.word	0xa				# Subsystem (EFI application)
174	.word	0				# DllCharacteristics
175#ifdef CONFIG_X86_32
176	.long	0				# SizeOfStackReserve
177	.long	0				# SizeOfStackCommit
178	.long	0				# SizeOfHeapReserve
179	.long	0				# SizeOfHeapCommit
180#else
181	.quad	0				# SizeOfStackReserve
182	.quad	0				# SizeOfStackCommit
183	.quad	0				# SizeOfHeapReserve
184	.quad	0				# SizeOfHeapCommit
185#endif
186	.long	0				# LoaderFlags
187	.long	0x6				# NumberOfRvaAndSizes
188
189	.quad	0				# ExportTable
190	.quad	0				# ImportTable
191	.quad	0				# ResourceTable
192	.quad	0				# ExceptionTable
193	.quad	0				# CertificationTable
194	.quad	0				# BaseRelocationTable
195
196	# Section table
197section_table:
198	#
199	# The offset & size fields are filled in by build.c.
200	#
201	.ascii	".setup"
202	.byte	0
203	.byte	0
204	.long	0
205	.long	0x0				# startup_{32,64}
206	.long	0				# Size of initialized data
207						# on disk
208	.long	0x0				# startup_{32,64}
209	.long	0				# PointerToRelocations
210	.long	0				# PointerToLineNumbers
211	.word	0				# NumberOfRelocations
212	.word	0				# NumberOfLineNumbers
213	.long	0x60500020			# Characteristics (section flags)
214
215	#
216	# The EFI application loader requires a relocation section
217	# because EFI applications must be relocatable. The .reloc
218	# offset & size fields are filled in by build.c.
219	#
220	.ascii	".reloc"
221	.byte	0
222	.byte	0
223	.long	0
224	.long	0
225	.long	0				# SizeOfRawData
226	.long	0				# PointerToRawData
227	.long	0				# PointerToRelocations
228	.long	0				# PointerToLineNumbers
229	.word	0				# NumberOfRelocations
230	.word	0				# NumberOfLineNumbers
231	.long	0x42100040			# Characteristics (section flags)
232
233	#
234	# The offset & size fields are filled in by build.c.
235	#
236	.ascii	".text"
237	.byte	0
238	.byte	0
239	.byte	0
240	.long	0
241	.long	0x0				# startup_{32,64}
242	.long	0				# Size of initialized data
243						# on disk
244	.long	0x0				# startup_{32,64}
245	.long	0				# PointerToRelocations
246	.long	0				# PointerToLineNumbers
247	.word	0				# NumberOfRelocations
248	.word	0				# NumberOfLineNumbers
249	.long	0x60500020			# Characteristics (section flags)
250
251	#
252	# The offset & size fields are filled in by build.c.
253	#
254	.ascii	".bss"
255	.byte	0
256	.byte	0
257	.byte	0
258	.byte	0
259	.long	0
260	.long	0x0
261	.long	0				# Size of initialized data
262						# on disk
263	.long	0x0
264	.long	0				# PointerToRelocations
265	.long	0				# PointerToLineNumbers
266	.word	0				# NumberOfRelocations
267	.word	0				# NumberOfLineNumbers
268	.long	0xc8000080			# Characteristics (section flags)
269
270#endif /* CONFIG_EFI_STUB */
271
272	# Kernel attributes; used by setup.  This is part 1 of the
273	# header, from the old boot sector.
274
275	.section ".header", "a"
276	.globl	sentinel
277sentinel:	.byte 0xff, 0xff        /* Used to detect broken loaders */
278
279	.globl	hdr
280hdr:
281setup_sects:	.byte 0			/* Filled in by build.c */
282root_flags:	.word ROOT_RDONLY
283syssize:	.long 0			/* Filled in by build.c */
284ram_size:	.word 0			/* Obsolete */
285vid_mode:	.word SVGA_MODE
286root_dev:	.word 0			/* Filled in by build.c */
287boot_flag:	.word 0xAA55
288
289	# offset 512, entry point
290
291	.globl	_start
292_start:
293		# Explicitly enter this as bytes, or the assembler
294		# tries to generate a 3-byte jump here, which causes
295		# everything else to push off to the wrong offset.
296		.byte	0xeb		# short (2-byte) jump
297		.byte	start_of_setup-1f
2981:
299
300	# Part 2 of the header, from the old setup.S
301
302		.ascii	"HdrS"		# header signature
303		.word	0x020d		# header version number (>= 0x0105)
304					# or else old loadlin-1.5 will fail)
305		.globl realmode_swtch
306realmode_swtch:	.word	0, 0		# default_switch, SETUPSEG
307start_sys_seg:	.word	SYSSEG		# obsolete and meaningless, but just
308					# in case something decided to "use" it
309		.word	kernel_version-512 # pointing to kernel version string
310					# above section of header is compatible
311					# with loadlin-1.5 (header v1.5). Don't
312					# change it.
313
314type_of_loader:	.byte	0		# 0 means ancient bootloader, newer
315					# bootloaders know to change this.
316					# See Documentation/x86/boot.txt for
317					# assigned ids
318
319# flags, unused bits must be zero (RFU) bit within loadflags
320loadflags:
321		.byte	LOADED_HIGH	# The kernel is to be loaded high
322
323setup_move_size: .word  0x8000		# size to move, when setup is not
324					# loaded at 0x90000. We will move setup
325					# to 0x90000 then just before jumping
326					# into the kernel. However, only the
327					# loader knows how much data behind
328					# us also needs to be loaded.
329
330code32_start:				# here loaders can put a different
331					# start address for 32-bit code.
332		.long	0x100000	# 0x100000 = default for big kernel
333
334ramdisk_image:	.long	0		# address of loaded ramdisk image
335					# Here the loader puts the 32-bit
336					# address where it loaded the image.
337					# This only will be read by the kernel.
338
339ramdisk_size:	.long	0		# its size in bytes
340
341bootsect_kludge:
342		.long	0		# obsolete
343
344heap_end_ptr:	.word	_end+STACK_SIZE-512
345					# (Header version 0x0201 or later)
346					# space from here (exclusive) down to
347					# end of setup code can be used by setup
348					# for local heap purposes.
349
350ext_loader_ver:
351		.byte	0		# Extended boot loader version
352ext_loader_type:
353		.byte	0		# Extended boot loader type
354
355cmd_line_ptr:	.long	0		# (Header version 0x0202 or later)
356					# If nonzero, a 32-bit pointer
357					# to the kernel command line.
358					# The command line should be
359					# located between the start of
360					# setup and the end of low
361					# memory (0xa0000), or it may
362					# get overwritten before it
363					# gets read.  If this field is
364					# used, there is no longer
365					# anything magical about the
366					# 0x90000 segment; the setup
367					# can be located anywhere in
368					# low memory 0x10000 or higher.
369
370initrd_addr_max: .long 0x7fffffff
371					# (Header version 0x0203 or later)
372					# The highest safe address for
373					# the contents of an initrd
374					# The current kernel allows up to 4 GB,
375					# but leave it at 2 GB to avoid
376					# possible bootloader bugs.
377
378kernel_alignment:  .long CONFIG_PHYSICAL_ALIGN	#physical addr alignment
379						#required for protected mode
380						#kernel
381#ifdef CONFIG_RELOCATABLE
382relocatable_kernel:    .byte 1
383#else
384relocatable_kernel:    .byte 0
385#endif
386min_alignment:		.byte MIN_KERNEL_ALIGN_LG2	# minimum alignment
387
388xloadflags:
389#ifdef CONFIG_X86_64
390# define XLF0 XLF_KERNEL_64			/* 64-bit kernel */
391#else
392# define XLF0 0
393#endif
394
395#if defined(CONFIG_RELOCATABLE) && defined(CONFIG_X86_64)
396   /* kernel/boot_param/ramdisk could be loaded above 4g */
397# define XLF1 XLF_CAN_BE_LOADED_ABOVE_4G
398#else
399# define XLF1 0
400#endif
401
402#ifdef CONFIG_EFI_STUB
403# ifdef CONFIG_EFI_MIXED
404#  define XLF23 (XLF_EFI_HANDOVER_32|XLF_EFI_HANDOVER_64)
405# else
406#  ifdef CONFIG_X86_64
407#   define XLF23 XLF_EFI_HANDOVER_64		/* 64-bit EFI handover ok */
408#  else
409#   define XLF23 XLF_EFI_HANDOVER_32		/* 32-bit EFI handover ok */
410#  endif
411# endif
412#else
413# define XLF23 0
414#endif
415
416#if defined(CONFIG_X86_64) && defined(CONFIG_EFI) && defined(CONFIG_KEXEC_CORE)
417# define XLF4 XLF_EFI_KEXEC
418#else
419# define XLF4 0
420#endif
421
422			.word XLF0 | XLF1 | XLF23 | XLF4
423
424cmdline_size:   .long   COMMAND_LINE_SIZE-1     #length of the command line,
425                                                #added with boot protocol
426                                                #version 2.06
427
428hardware_subarch:	.long 0			# subarchitecture, added with 2.07
429						# default to 0 for normal x86 PC
430
431hardware_subarch_data:	.quad 0
432
433payload_offset:		.long ZO_input_data
434payload_length:		.long ZO_z_input_len
435
436setup_data:		.quad 0			# 64-bit physical pointer to
437						# single linked list of
438						# struct setup_data
439
440pref_address:		.quad LOAD_PHYSICAL_ADDR	# preferred load addr
441
442#
443# Getting to provably safe in-place decompression is hard. Worst case
444# behaviours need to be analyzed. Here let's take the decompression of
445# a gzip-compressed kernel as example, to illustrate it:
446#
447# The file layout of gzip compressed kernel is:
448#
449#    magic[2]
450#    method[1]
451#    flags[1]
452#    timestamp[4]
453#    extraflags[1]
454#    os[1]
455#    compressed data blocks[N]
456#    crc[4] orig_len[4]
457#
458# ... resulting in +18 bytes overhead of uncompressed data.
459#
460# (For more information, please refer to RFC 1951 and RFC 1952.)
461#
462# Files divided into blocks
463# 1 bit (last block flag)
464# 2 bits (block type)
465#
466# 1 block occurs every 32K -1 bytes or when there 50% compression
467# has been achieved. The smallest block type encoding is always used.
468#
469# stored:
470#    32 bits length in bytes.
471#
472# fixed:
473#    magic fixed tree.
474#    symbols.
475#
476# dynamic:
477#    dynamic tree encoding.
478#    symbols.
479#
480#
481# The buffer for decompression in place is the length of the uncompressed
482# data, plus a small amount extra to keep the algorithm safe. The
483# compressed data is placed at the end of the buffer.  The output pointer
484# is placed at the start of the buffer and the input pointer is placed
485# where the compressed data starts. Problems will occur when the output
486# pointer overruns the input pointer.
487#
488# The output pointer can only overrun the input pointer if the input
489# pointer is moving faster than the output pointer.  A condition only
490# triggered by data whose compressed form is larger than the uncompressed
491# form.
492#
493# The worst case at the block level is a growth of the compressed data
494# of 5 bytes per 32767 bytes.
495#
496# The worst case internal to a compressed block is very hard to figure.
497# The worst case can at least be bounded by having one bit that represents
498# 32764 bytes and then all of the rest of the bytes representing the very
499# very last byte.
500#
501# All of which is enough to compute an amount of extra data that is required
502# to be safe.  To avoid problems at the block level allocating 5 extra bytes
503# per 32767 bytes of data is sufficient.  To avoid problems internal to a
504# block adding an extra 32767 bytes (the worst case uncompressed block size)
505# is sufficient, to ensure that in the worst case the decompressed data for
506# block will stop the byte before the compressed data for a block begins.
507# To avoid problems with the compressed data's meta information an extra 18
508# bytes are needed.  Leading to the formula:
509#
510# extra_bytes = (uncompressed_size >> 12) + 32768 + 18
511#
512# Adding 8 bytes per 32K is a bit excessive but much easier to calculate.
513# Adding 32768 instead of 32767 just makes for round numbers.
514#
515# Above analysis is for decompressing gzip compressed kernel only. Up to
516# now 6 different decompressor are supported all together. And among them
517# xz stores data in chunks and has maximum chunk of 64K. Hence safety
518# margin should be updated to cover all decompressors so that we don't
519# need to deal with each of them separately. Please check
520# the description in lib/decompressor_xxx.c for specific information.
521#
522# extra_bytes = (uncompressed_size >> 12) + 65536 + 128
523
524#define ZO_z_extra_bytes	((ZO_z_output_len >> 12) + 65536 + 128)
525#if ZO_z_output_len > ZO_z_input_len
526# define ZO_z_extract_offset	(ZO_z_output_len + ZO_z_extra_bytes - \
527				 ZO_z_input_len)
528#else
529# define ZO_z_extract_offset	ZO_z_extra_bytes
530#endif
531
532/*
533 * The extract_offset has to be bigger than ZO head section. Otherwise when
534 * the head code is running to move ZO to the end of the buffer, it will
535 * overwrite the head code itself.
536 */
537#if (ZO__ehead - ZO_startup_32) > ZO_z_extract_offset
538# define ZO_z_min_extract_offset ((ZO__ehead - ZO_startup_32 + 4095) & ~4095)
539#else
540# define ZO_z_min_extract_offset ((ZO_z_extract_offset + 4095) & ~4095)
541#endif
542
543#define ZO_INIT_SIZE	(ZO__end - ZO_startup_32 + ZO_z_min_extract_offset)
544
545#define VO_INIT_SIZE	(VO__end - VO__text)
546#if ZO_INIT_SIZE > VO_INIT_SIZE
547# define INIT_SIZE ZO_INIT_SIZE
548#else
549# define INIT_SIZE VO_INIT_SIZE
550#endif
551
552init_size:		.long INIT_SIZE		# kernel initialization size
553handover_offset:	.long 0			# Filled in by build.c
554
555# End of setup header #####################################################
556
557	.section ".entrytext", "ax"
558start_of_setup:
559# Force %es = %ds
560	movw	%ds, %ax
561	movw	%ax, %es
562	cld
563
564# Apparently some ancient versions of LILO invoked the kernel with %ss != %ds,
565# which happened to work by accident for the old code.  Recalculate the stack
566# pointer if %ss is invalid.  Otherwise leave it alone, LOADLIN sets up the
567# stack behind its own code, so we can't blindly put it directly past the heap.
568
569	movw	%ss, %dx
570	cmpw	%ax, %dx	# %ds == %ss?
571	movw	%sp, %dx
572	je	2f		# -> assume %sp is reasonably set
573
574	# Invalid %ss, make up a new stack
575	movw	$_end, %dx
576	testb	$CAN_USE_HEAP, loadflags
577	jz	1f
578	movw	heap_end_ptr, %dx
5791:	addw	$STACK_SIZE, %dx
580	jnc	2f
581	xorw	%dx, %dx	# Prevent wraparound
582
5832:	# Now %dx should point to the end of our stack space
584	andw	$~3, %dx	# dword align (might as well...)
585	jnz	3f
586	movw	$0xfffc, %dx	# Make sure we're not zero
5873:	movw	%ax, %ss
588	movzwl	%dx, %esp	# Clear upper half of %esp
589	sti			# Now we should have a working stack
590
591# We will have entered with %cs = %ds+0x20, normalize %cs so
592# it is on par with the other segments.
593	pushw	%ds
594	pushw	$6f
595	lretw
5966:
597
598# Check signature at end of setup
599	cmpl	$0x5a5aaa55, setup_sig
600	jne	setup_bad
601
602# Zero the bss
603	movw	$__bss_start, %di
604	movw	$_end+3, %cx
605	xorl	%eax, %eax
606	subw	%di, %cx
607	shrw	$2, %cx
608	rep; stosl
609
610# Jump to C code (should not return)
611	calll	main
612
613# Setup corrupt somehow...
614setup_bad:
615	movl	$setup_corrupt, %eax
616	calll	puts
617	# Fall through...
618
619	.globl	die
620	.type	die, @function
621die:
622	hlt
623	jmp	die
624
625	.size	die, .-die
626
627	.section ".initdata", "a"
628setup_corrupt:
629	.byte	7
630	.string	"No setup signature found...\n"
631