1/* SPDX-License-Identifier: GPL-2.0 */
  2/*
  3 *  linux/boot/head.S
  4 *
  5 *  Copyright (C) 1991, 1992, 1993  Linus Torvalds
  6 */
  7
  8/*
  9 *  head.S contains the 32-bit startup code.
 10 *
 11 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where
 12 * the page directory will exist. The startup code will be overwritten by
 13 * the page directory. [According to comments etc elsewhere on a compressed
 14 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
 15 *
 16 * Page 0 is deliberately kept safe, since System Management Mode code in
 17 * laptops may need to access the BIOS data stored there.  This is also
 18 * useful for future device drivers that either access the BIOS via VM86
 19 * mode.
 20 */
 21
 22/*
 23 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
 24 */
 25	.text
 26
 27#include <linux/init.h>
 28#include <linux/linkage.h>
 29#include <asm/segment.h>
 30#include <asm/page_types.h>
 31#include <asm/boot.h>
 32#include <asm/asm-offsets.h>
 33#include <asm/bootparam.h>
 34
 35/*
 36 * These symbols needed to be marked as .hidden to prevent the BFD linker from
 37 * generating R_386_32 (rather than R_386_RELATIVE) relocations for them when
 38 * the 32-bit compressed kernel is linked as PIE. This is no longer necessary,
 39 * but it doesn't hurt to keep them .hidden.
 40 */
 41	.hidden _bss
 42	.hidden _ebss
 43	.hidden _end
 44
 45	__HEAD
 46SYM_FUNC_START(startup_32)
 47	cld
 48	cli
 49
 50/*
 51 * Calculate the delta between where we were compiled to run
 52 * at and where we were actually loaded at.  This can only be done
 53 * with a short local call on x86.  Nothing  else will tell us what
 54 * address we are running at.  The reserved chunk of the real-mode
 55 * data at 0x1e4 (defined as a scratch field) are used as the stack
 56 * for this calculation. Only 4 bytes are needed.
 57 */
 58	leal	(BP_scratch+4)(%esi), %esp
 59	call	1f
 601:	popl	%edx
 61	addl	$_GLOBAL_OFFSET_TABLE_+(.-1b), %edx
 62
 63	/* Load new GDT */
 64	leal	gdt@GOTOFF(%edx), %eax
 65	movl	%eax, 2(%eax)
 66	lgdt	(%eax)
 67
 68	/* Load segment registers with our descriptors */
 69	movl	$__BOOT_DS, %eax
 70	movl	%eax, %ds
 71	movl	%eax, %es
 72	movl	%eax, %fs
 73	movl	%eax, %gs
 74	movl	%eax, %ss
 75
 76/*
 77 * %edx contains the address we are loaded at by the boot loader (plus the
 78 * offset to the GOT).  The below code calculates %ebx to be the address where
 79 * we should move the kernel image temporarily for safe in-place decompression
 80 * (again, plus the offset to the GOT).
 81 *
 82 * %ebp is calculated to be the address that the kernel will be decompressed to.
 83 */
 84
 85#ifdef CONFIG_RELOCATABLE
 86	leal	startup_32@GOTOFF(%edx), %ebx
 87	movl	BP_kernel_alignment(%esi), %eax
 88	decl	%eax
 89	addl    %eax, %ebx
 90	notl	%eax
 91	andl    %eax, %ebx
 92	cmpl	$LOAD_PHYSICAL_ADDR, %ebx
 93	jae	1f
 94#endif
 95	movl	$LOAD_PHYSICAL_ADDR, %ebx
 961:
 97
 98	movl	%ebx, %ebp	// Save the output address for later
 99	/* Target address to relocate to for decompression */
100	addl    BP_init_size(%esi), %ebx
101	subl    $_end@GOTOFF, %ebx
102
103	/* Set up the stack */
104	leal	boot_stack_end@GOTOFF(%ebx), %esp
105
106	/* Zero EFLAGS */
107	pushl	$0
108	popfl
109
110/*
111 * Copy the compressed kernel to the end of our buffer
112 * where decompression in place becomes safe.
113 */
114	pushl	%esi
115	leal	(_bss@GOTOFF-4)(%edx), %esi
116	leal	(_bss@GOTOFF-4)(%ebx), %edi
117	movl	$(_bss - startup_32), %ecx
118	shrl	$2, %ecx
119	std
120	rep	movsl
121	cld
122	popl	%esi
123
124	/*
125	 * The GDT may get overwritten either during the copy we just did or
126	 * during extract_kernel below. To avoid any issues, repoint the GDTR
127	 * to the new copy of the GDT.
128	 */
129	leal	gdt@GOTOFF(%ebx), %eax
130	movl	%eax, 2(%eax)
131	lgdt	(%eax)
132
133/*
134 * Jump to the relocated address.
135 */
136	leal	.Lrelocated@GOTOFF(%ebx), %eax
137	jmp	*%eax
138SYM_FUNC_END(startup_32)
139
140	.text
141SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
142
143/*
144 * Clear BSS (stack is currently empty)
145 */
146	xorl	%eax, %eax
147	leal	_bss@GOTOFF(%ebx), %edi
148	leal	_ebss@GOTOFF(%ebx), %ecx
149	subl	%edi, %ecx
150	shrl	$2, %ecx
151	rep	stosl
152
153/*
154 * Do the extraction, and jump to the new kernel..
155 */
156	/* push arguments for extract_kernel: */
157
158	pushl	%ebp			/* output address */
159	pushl	%esi			/* real mode pointer */
160	call	extract_kernel		/* returns kernel entry point in %eax */
161	addl	$24, %esp
162
163/*
164 * Jump to the extracted kernel.
165 */
166	xorl	%ebx, %ebx
167	jmp	*%eax
168SYM_FUNC_END(.Lrelocated)
169
170	.data
171	.balign	8
172SYM_DATA_START_LOCAL(gdt)
173	.word	gdt_end - gdt - 1
174	.long	0
175	.word	0
176	.quad	0x0000000000000000	/* Reserved */
177	.quad	0x00cf9a000000ffff	/* __KERNEL_CS */
178	.quad	0x00cf92000000ffff	/* __KERNEL_DS */
179SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
180
181/*
182 * Stack and heap for uncompression
183 */
184	.bss
185	.balign 4
186boot_stack:
187	.fill BOOT_STACK_SIZE, 1, 0
188boot_stack_end: