xref: /openbmc/linux/arch/x86/boot/header.S (revision 0a962f2f)
1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 *	header.S
4 *
5 *	Copyright (C) 1991, 1992 Linus Torvalds
6 *
7 *	Based on bootsect.S and setup.S
8 *	modified by more people than can be counted
9 *
10 *	Rewritten as a common file by H. Peter Anvin (Apr 2007)
11 *
12 * BIG FAT NOTE: We're in real mode using 64k segments.  Therefore segment
13 * addresses must be multiplied by 16 to obtain their respective linear
14 * addresses. To avoid confusion, linear addresses are written using leading
15 * hex while segment addresses are written as segment:offset.
16 *
17 */
18#include <linux/pe.h>
19#include <asm/segment.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	.set	salign, 0x1000
40	.set	falign, 0x200
41
42	.code16
43	.section ".bstext", "ax"
44#ifdef CONFIG_EFI_STUB
45	# "MZ", MS-DOS header
46	.word	MZ_MAGIC
47	.org	0x38
48	#
49	# Offset to the PE header.
50	#
51	.long	LINUX_PE_MAGIC
52	.long	pe_header
53pe_header:
54	.long	PE_MAGIC
55
56coff_header:
57#ifdef CONFIG_X86_32
58	.set	image_file_add_flags, IMAGE_FILE_32BIT_MACHINE
59	.set	pe_opt_magic, PE_OPT_MAGIC_PE32
60	.word	IMAGE_FILE_MACHINE_I386
61#else
62	.set	image_file_add_flags, 0
63	.set	pe_opt_magic, PE_OPT_MAGIC_PE32PLUS
64	.word	IMAGE_FILE_MACHINE_AMD64
65#endif
66	.word	section_count			# nr_sections
67	.long	0 				# TimeDateStamp
68	.long	0				# PointerToSymbolTable
69	.long	1				# NumberOfSymbols
70	.word	section_table - optional_header	# SizeOfOptionalHeader
71	.word	IMAGE_FILE_EXECUTABLE_IMAGE	| \
72		image_file_add_flags		| \
73		IMAGE_FILE_DEBUG_STRIPPED	| \
74		IMAGE_FILE_LINE_NUMS_STRIPPED	# Characteristics
75
76optional_header:
77	.word	pe_opt_magic
78	.byte	0x02				# MajorLinkerVersion
79	.byte	0x14				# MinorLinkerVersion
80
81	.long	ZO__data			# SizeOfCode
82
83	.long	ZO__end - ZO__data		# SizeOfInitializedData
84	.long	0				# SizeOfUninitializedData
85
86	.long	setup_size + ZO_efi_pe_entry	# AddressOfEntryPoint
87
88	.long	setup_size			# BaseOfCode
89#ifdef CONFIG_X86_32
90	.long	0				# data
91#endif
92
93extra_header_fields:
94#ifdef CONFIG_X86_32
95	.long	0				# ImageBase
96#else
97	.quad	0				# ImageBase
98#endif
99	.long	salign				# SectionAlignment
100	.long	falign				# FileAlignment
101	.word	0				# MajorOperatingSystemVersion
102	.word	0				# MinorOperatingSystemVersion
103	.word	LINUX_EFISTUB_MAJOR_VERSION	# MajorImageVersion
104	.word	LINUX_EFISTUB_MINOR_VERSION	# MinorImageVersion
105	.word	0				# MajorSubsystemVersion
106	.word	0				# MinorSubsystemVersion
107	.long	0				# Win32VersionValue
108
109	.long	setup_size + ZO__end		# SizeOfImage
110
111	.long	salign				# SizeOfHeaders
112	.long	0				# CheckSum
113	.word	IMAGE_SUBSYSTEM_EFI_APPLICATION	# Subsystem (EFI application)
114#ifdef CONFIG_EFI_DXE_MEM_ATTRIBUTES
115	.word	IMAGE_DLL_CHARACTERISTICS_NX_COMPAT	# DllCharacteristics
116#else
117	.word	0				# DllCharacteristics
118#endif
119#ifdef CONFIG_X86_32
120	.long	0				# SizeOfStackReserve
121	.long	0				# SizeOfStackCommit
122	.long	0				# SizeOfHeapReserve
123	.long	0				# SizeOfHeapCommit
124#else
125	.quad	0				# SizeOfStackReserve
126	.quad	0				# SizeOfStackCommit
127	.quad	0				# SizeOfHeapReserve
128	.quad	0				# SizeOfHeapCommit
129#endif
130	.long	0				# LoaderFlags
131	.long	(section_table - .) / 8		# NumberOfRvaAndSizes
132
133	.quad	0				# ExportTable
134	.quad	0				# ImportTable
135	.quad	0				# ResourceTable
136	.quad	0				# ExceptionTable
137	.quad	0				# CertificationTable
138	.quad	0				# BaseRelocationTable
139
140	# Section table
141section_table:
142	.ascii	".setup"
143	.byte	0
144	.byte	0
145	.long	pecompat_fstart - salign 	# VirtualSize
146	.long	salign				# VirtualAddress
147	.long	pecompat_fstart - salign	# SizeOfRawData
148	.long	salign				# PointerToRawData
149
150	.long	0, 0, 0
151	.long	IMAGE_SCN_CNT_INITIALIZED_DATA	| \
152		IMAGE_SCN_MEM_READ		| \
153		IMAGE_SCN_MEM_DISCARDABLE	# Characteristics
154
155#ifdef CONFIG_EFI_MIXED
156	.asciz	".compat"
157
158	.long	pecompat_fsize			# VirtualSize
159	.long	pecompat_fstart			# VirtualAddress
160	.long	pecompat_fsize			# SizeOfRawData
161	.long	pecompat_fstart			# PointerToRawData
162
163	.long	0, 0, 0
164	.long	IMAGE_SCN_CNT_INITIALIZED_DATA	| \
165		IMAGE_SCN_MEM_READ		| \
166		IMAGE_SCN_MEM_DISCARDABLE	# Characteristics
167
168	/*
169	 * Put the IA-32 machine type and the associated entry point address in
170	 * the .compat section, so loaders can figure out which other execution
171	 * modes this image supports.
172	 */
173	.pushsection ".pecompat", "a", @progbits
174	.balign	salign
175	.globl	pecompat_fstart
176pecompat_fstart:
177	.byte	0x1				# Version
178	.byte	8				# Size
179	.word	IMAGE_FILE_MACHINE_I386		# PE machine type
180	.long	setup_size + ZO_efi32_pe_entry	# Entrypoint
181	.byte	0x0				# Sentinel
182	.popsection
183#else
184	.set	pecompat_fstart, setup_size
185#endif
186	.ascii	".text"
187	.byte	0
188	.byte	0
189	.byte	0
190	.long	ZO__data
191	.long	setup_size
192	.long	ZO__data			# Size of initialized data
193						# on disk
194	.long	setup_size
195	.long	0				# PointerToRelocations
196	.long	0				# PointerToLineNumbers
197	.word	0				# NumberOfRelocations
198	.word	0				# NumberOfLineNumbers
199	.long	IMAGE_SCN_CNT_CODE		| \
200		IMAGE_SCN_MEM_READ		| \
201		IMAGE_SCN_MEM_EXECUTE		# Characteristics
202
203	.ascii	".data\0\0\0"
204	.long	ZO__end - ZO__data		# VirtualSize
205	.long	setup_size + ZO__data		# VirtualAddress
206	.long	ZO__edata - ZO__data		# SizeOfRawData
207	.long	setup_size + ZO__data		# PointerToRawData
208
209	.long	0, 0, 0
210	.long	IMAGE_SCN_CNT_INITIALIZED_DATA	| \
211		IMAGE_SCN_MEM_READ		| \
212		IMAGE_SCN_MEM_WRITE		# Characteristics
213
214	.set	section_count, (. - section_table) / 40
215#endif /* CONFIG_EFI_STUB */
216
217	# Kernel attributes; used by setup.  This is part 1 of the
218	# header, from the old boot sector.
219
220	.section ".header", "a"
221	.globl	sentinel
222sentinel:	.byte 0xff, 0xff        /* Used to detect broken loaders */
223
224	.globl	hdr
225hdr:
226		.byte setup_sects - 1
227root_flags:	.word ROOT_RDONLY
228syssize:	.long ZO__edata / 16
229ram_size:	.word 0			/* Obsolete */
230vid_mode:	.word SVGA_MODE
231root_dev:	.word 0			/* Default to major/minor 0/0 */
232boot_flag:	.word 0xAA55
233
234	# offset 512, entry point
235
236	.globl	_start
237_start:
238		# Explicitly enter this as bytes, or the assembler
239		# tries to generate a 3-byte jump here, which causes
240		# everything else to push off to the wrong offset.
241		.byte	0xeb		# short (2-byte) jump
242		.byte	start_of_setup-1f
2431:
244
245	# Part 2 of the header, from the old setup.S
246
247		.ascii	"HdrS"		# header signature
248		.word	0x020f		# header version number (>= 0x0105)
249					# or else old loadlin-1.5 will fail)
250		.globl realmode_swtch
251realmode_swtch:	.word	0, 0		# default_switch, SETUPSEG
252start_sys_seg:	.word	SYSSEG		# obsolete and meaningless, but just
253					# in case something decided to "use" it
254		.word	kernel_version-512 # pointing to kernel version string
255					# above section of header is compatible
256					# with loadlin-1.5 (header v1.5). Don't
257					# change it.
258
259type_of_loader:	.byte	0		# 0 means ancient bootloader, newer
260					# bootloaders know to change this.
261					# See Documentation/arch/x86/boot.rst for
262					# assigned ids
263
264# flags, unused bits must be zero (RFU) bit within loadflags
265loadflags:
266		.byte	LOADED_HIGH	# The kernel is to be loaded high
267
268setup_move_size: .word  0x8000		# size to move, when setup is not
269					# loaded at 0x90000. We will move setup
270					# to 0x90000 then just before jumping
271					# into the kernel. However, only the
272					# loader knows how much data behind
273					# us also needs to be loaded.
274
275code32_start:				# here loaders can put a different
276					# start address for 32-bit code.
277		.long	0x100000	# 0x100000 = default for big kernel
278
279ramdisk_image:	.long	0		# address of loaded ramdisk image
280					# Here the loader puts the 32-bit
281					# address where it loaded the image.
282					# This only will be read by the kernel.
283
284ramdisk_size:	.long	0		# its size in bytes
285
286bootsect_kludge:
287		.long	0		# obsolete
288
289heap_end_ptr:	.word	_end+STACK_SIZE-512
290					# (Header version 0x0201 or later)
291					# space from here (exclusive) down to
292					# end of setup code can be used by setup
293					# for local heap purposes.
294
295ext_loader_ver:
296		.byte	0		# Extended boot loader version
297ext_loader_type:
298		.byte	0		# Extended boot loader type
299
300cmd_line_ptr:	.long	0		# (Header version 0x0202 or later)
301					# If nonzero, a 32-bit pointer
302					# to the kernel command line.
303					# The command line should be
304					# located between the start of
305					# setup and the end of low
306					# memory (0xa0000), or it may
307					# get overwritten before it
308					# gets read.  If this field is
309					# used, there is no longer
310					# anything magical about the
311					# 0x90000 segment; the setup
312					# can be located anywhere in
313					# low memory 0x10000 or higher.
314
315initrd_addr_max: .long 0x7fffffff
316					# (Header version 0x0203 or later)
317					# The highest safe address for
318					# the contents of an initrd
319					# The current kernel allows up to 4 GB,
320					# but leave it at 2 GB to avoid
321					# possible bootloader bugs.
322
323kernel_alignment:  .long CONFIG_PHYSICAL_ALIGN	#physical addr alignment
324						#required for protected mode
325						#kernel
326#ifdef CONFIG_RELOCATABLE
327relocatable_kernel:    .byte 1
328#else
329relocatable_kernel:    .byte 0
330#endif
331min_alignment:		.byte MIN_KERNEL_ALIGN_LG2	# minimum alignment
332
333xloadflags:
334#ifdef CONFIG_X86_64
335# define XLF0 XLF_KERNEL_64			/* 64-bit kernel */
336#else
337# define XLF0 0
338#endif
339
340#if defined(CONFIG_RELOCATABLE) && defined(CONFIG_X86_64)
341   /* kernel/boot_param/ramdisk could be loaded above 4g */
342# define XLF1 XLF_CAN_BE_LOADED_ABOVE_4G
343#else
344# define XLF1 0
345#endif
346
347#ifdef CONFIG_EFI_HANDOVER_PROTOCOL
348# ifdef CONFIG_EFI_MIXED
349#  define XLF23 (XLF_EFI_HANDOVER_32|XLF_EFI_HANDOVER_64)
350# else
351#  ifdef CONFIG_X86_64
352#   define XLF23 XLF_EFI_HANDOVER_64		/* 64-bit EFI handover ok */
353#  else
354#   define XLF23 XLF_EFI_HANDOVER_32		/* 32-bit EFI handover ok */
355#  endif
356# endif
357#else
358# define XLF23 0
359#endif
360
361#if defined(CONFIG_X86_64) && defined(CONFIG_EFI) && defined(CONFIG_KEXEC_CORE)
362# define XLF4 XLF_EFI_KEXEC
363#else
364# define XLF4 0
365#endif
366
367#ifdef CONFIG_X86_64
368#ifdef CONFIG_X86_5LEVEL
369#define XLF56 (XLF_5LEVEL|XLF_5LEVEL_ENABLED)
370#else
371#define XLF56 XLF_5LEVEL
372#endif
373#else
374#define XLF56 0
375#endif
376
377			.word XLF0 | XLF1 | XLF23 | XLF4 | XLF56
378
379cmdline_size:   .long   COMMAND_LINE_SIZE-1     #length of the command line,
380                                                #added with boot protocol
381                                                #version 2.06
382
383hardware_subarch:	.long 0			# subarchitecture, added with 2.07
384						# default to 0 for normal x86 PC
385
386hardware_subarch_data:	.quad 0
387
388payload_offset:		.long ZO_input_data
389payload_length:		.long ZO_z_input_len
390
391setup_data:		.quad 0			# 64-bit physical pointer to
392						# single linked list of
393						# struct setup_data
394
395pref_address:		.quad LOAD_PHYSICAL_ADDR	# preferred load addr
396
397#
398# Getting to provably safe in-place decompression is hard. Worst case
399# behaviours need to be analyzed. Here let's take the decompression of
400# a gzip-compressed kernel as example, to illustrate it:
401#
402# The file layout of gzip compressed kernel is:
403#
404#    magic[2]
405#    method[1]
406#    flags[1]
407#    timestamp[4]
408#    extraflags[1]
409#    os[1]
410#    compressed data blocks[N]
411#    crc[4] orig_len[4]
412#
413# ... resulting in +18 bytes overhead of uncompressed data.
414#
415# (For more information, please refer to RFC 1951 and RFC 1952.)
416#
417# Files divided into blocks
418# 1 bit (last block flag)
419# 2 bits (block type)
420#
421# 1 block occurs every 32K -1 bytes or when there 50% compression
422# has been achieved. The smallest block type encoding is always used.
423#
424# stored:
425#    32 bits length in bytes.
426#
427# fixed:
428#    magic fixed tree.
429#    symbols.
430#
431# dynamic:
432#    dynamic tree encoding.
433#    symbols.
434#
435#
436# The buffer for decompression in place is the length of the uncompressed
437# data, plus a small amount extra to keep the algorithm safe. The
438# compressed data is placed at the end of the buffer.  The output pointer
439# is placed at the start of the buffer and the input pointer is placed
440# where the compressed data starts. Problems will occur when the output
441# pointer overruns the input pointer.
442#
443# The output pointer can only overrun the input pointer if the input
444# pointer is moving faster than the output pointer.  A condition only
445# triggered by data whose compressed form is larger than the uncompressed
446# form.
447#
448# The worst case at the block level is a growth of the compressed data
449# of 5 bytes per 32767 bytes.
450#
451# The worst case internal to a compressed block is very hard to figure.
452# The worst case can at least be bounded by having one bit that represents
453# 32764 bytes and then all of the rest of the bytes representing the very
454# very last byte.
455#
456# All of which is enough to compute an amount of extra data that is required
457# to be safe.  To avoid problems at the block level allocating 5 extra bytes
458# per 32767 bytes of data is sufficient.  To avoid problems internal to a
459# block adding an extra 32767 bytes (the worst case uncompressed block size)
460# is sufficient, to ensure that in the worst case the decompressed data for
461# block will stop the byte before the compressed data for a block begins.
462# To avoid problems with the compressed data's meta information an extra 18
463# bytes are needed.  Leading to the formula:
464#
465# extra_bytes = (uncompressed_size >> 12) + 32768 + 18
466#
467# Adding 8 bytes per 32K is a bit excessive but much easier to calculate.
468# Adding 32768 instead of 32767 just makes for round numbers.
469#
470# Above analysis is for decompressing gzip compressed kernel only. Up to
471# now 6 different decompressor are supported all together. And among them
472# xz stores data in chunks and has maximum chunk of 64K. Hence safety
473# margin should be updated to cover all decompressors so that we don't
474# need to deal with each of them separately. Please check
475# the description in lib/decompressor_xxx.c for specific information.
476#
477# extra_bytes = (uncompressed_size >> 12) + 65536 + 128
478#
479# LZ4 is even worse: data that cannot be further compressed grows by 0.4%,
480# or one byte per 256 bytes. OTOH, we can safely get rid of the +128 as
481# the size-dependent part now grows so fast.
482#
483# extra_bytes = (uncompressed_size >> 8) + 65536
484#
485# ZSTD compressed data grows by at most 3 bytes per 128K, and only has a 22
486# byte fixed overhead but has a maximum block size of 128K, so it needs a
487# larger margin.
488#
489# extra_bytes = (uncompressed_size >> 8) + 131072
490
491#define ZO_z_extra_bytes	((ZO_z_output_len >> 8) + 131072)
492#if ZO_z_output_len > ZO_z_input_len
493# define ZO_z_extract_offset	(ZO_z_output_len + ZO_z_extra_bytes - \
494				 ZO_z_input_len)
495#else
496# define ZO_z_extract_offset	ZO_z_extra_bytes
497#endif
498
499/*
500 * The extract_offset has to be bigger than ZO head section. Otherwise when
501 * the head code is running to move ZO to the end of the buffer, it will
502 * overwrite the head code itself.
503 */
504#if (ZO__ehead - ZO_startup_32) > ZO_z_extract_offset
505# define ZO_z_min_extract_offset ((ZO__ehead - ZO_startup_32 + 4095) & ~4095)
506#else
507# define ZO_z_min_extract_offset ((ZO_z_extract_offset + 4095) & ~4095)
508#endif
509
510#define ZO_INIT_SIZE	(ZO__end - ZO_startup_32 + ZO_z_min_extract_offset)
511
512#define VO_INIT_SIZE	(VO__end - VO__text)
513#if ZO_INIT_SIZE > VO_INIT_SIZE
514# define INIT_SIZE ZO_INIT_SIZE
515#else
516# define INIT_SIZE VO_INIT_SIZE
517#endif
518
519	.macro		__handover_offset
520#ifndef CONFIG_EFI_HANDOVER_PROTOCOL
521	.long		0
522#elif !defined(CONFIG_X86_64)
523	.long		ZO_efi32_stub_entry
524#else
525	/* Yes, this is really how we defined it :( */
526	.long		ZO_efi64_stub_entry - 0x200
527#ifdef CONFIG_EFI_MIXED
528	.if		ZO_efi32_stub_entry != ZO_efi64_stub_entry - 0x200
529	.error		"32-bit and 64-bit EFI entry points do not match"
530	.endif
531#endif
532#endif
533	.endm
534
535init_size:		.long INIT_SIZE		# kernel initialization size
536handover_offset:	__handover_offset
537kernel_info_offset:	.long ZO_kernel_info
538
539# End of setup header #####################################################
540
541	.section ".entrytext", "ax"
542start_of_setup:
543# Force %es = %ds
544	movw	%ds, %ax
545	movw	%ax, %es
546	cld
547
548# Apparently some ancient versions of LILO invoked the kernel with %ss != %ds,
549# which happened to work by accident for the old code.  Recalculate the stack
550# pointer if %ss is invalid.  Otherwise leave it alone, LOADLIN sets up the
551# stack behind its own code, so we can't blindly put it directly past the heap.
552
553	movw	%ss, %dx
554	cmpw	%ax, %dx	# %ds == %ss?
555	movw	%sp, %dx
556	je	2f		# -> assume %sp is reasonably set
557
558	# Invalid %ss, make up a new stack
559	movw	$_end, %dx
560	testb	$CAN_USE_HEAP, loadflags
561	jz	1f
562	movw	heap_end_ptr, %dx
5631:	addw	$STACK_SIZE, %dx
564	jnc	2f
565	xorw	%dx, %dx	# Prevent wraparound
566
5672:	# Now %dx should point to the end of our stack space
568	andw	$~3, %dx	# dword align (might as well...)
569	jnz	3f
570	movw	$0xfffc, %dx	# Make sure we're not zero
5713:	movw	%ax, %ss
572	movzwl	%dx, %esp	# Clear upper half of %esp
573	sti			# Now we should have a working stack
574
575# We will have entered with %cs = %ds+0x20, normalize %cs so
576# it is on par with the other segments.
577	pushw	%ds
578	pushw	$6f
579	lretw
5806:
581
582# Check signature at end of setup
583	cmpl	$0x5a5aaa55, setup_sig
584	jne	setup_bad
585
586# Zero the bss
587	movw	$__bss_start, %di
588	movw	$_end+3, %cx
589	xorl	%eax, %eax
590	subw	%di, %cx
591	shrw	$2, %cx
592	rep; stosl
593
594# Jump to C code (should not return)
595	calll	main
596
597# Setup corrupt somehow...
598setup_bad:
599	movl	$setup_corrupt, %eax
600	calll	puts
601	# Fall through...
602
603	.globl	die
604	.type	die, @function
605die:
606	hlt
607	jmp	die
608
609	.size	die, .-die
610
611	.section ".initdata", "a"
612setup_corrupt:
613	.byte	7
614	.string	"No setup signature found...\n"
615