xref: /openbmc/linux/arch/x86/boot/compressed/head_32.S (revision 22246614)
1/*
2 *  linux/boot/head.S
3 *
4 *  Copyright (C) 1991, 1992, 1993  Linus Torvalds
5 */
6
7/*
8 *  head.S contains the 32-bit startup code.
9 *
10 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where
11 * the page directory will exist. The startup code will be overwritten by
12 * the page directory. [According to comments etc elsewhere on a compressed
13 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
14 *
15 * Page 0 is deliberately kept safe, since System Management Mode code in
16 * laptops may need to access the BIOS data stored there.  This is also
17 * useful for future device drivers that either access the BIOS via VM86
18 * mode.
19 */
20
21/*
22 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
23 */
24.text
25
26#include <linux/linkage.h>
27#include <asm/segment.h>
28#include <asm/page.h>
29#include <asm/boot.h>
30#include <asm/asm-offsets.h>
31
32.section ".text.head","ax",@progbits
33	.globl startup_32
34
35startup_32:
36	cld
37	/* test KEEP_SEGMENTS flag to see if the bootloader is asking
38	 * us to not reload segments */
39	testb $(1<<6), BP_loadflags(%esi)
40	jnz 1f
41
42	cli
43	movl $(__BOOT_DS),%eax
44	movl %eax,%ds
45	movl %eax,%es
46	movl %eax,%fs
47	movl %eax,%gs
48	movl %eax,%ss
491:
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 (0x1e4+4)(%esi), %esp
59	call 1f
601:	popl %ebp
61	subl $1b, %ebp
62
63/* %ebp contains the address we are loaded at by the boot loader and %ebx
64 * contains the address where we should move the kernel image temporarily
65 * for safe in-place decompression.
66 */
67
68#ifdef CONFIG_RELOCATABLE
69	movl 	%ebp, %ebx
70	addl    $(CONFIG_PHYSICAL_ALIGN - 1), %ebx
71	andl    $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebx
72#else
73	movl $LOAD_PHYSICAL_ADDR, %ebx
74#endif
75
76	/* Replace the compressed data size with the uncompressed size */
77	subl input_len(%ebp), %ebx
78	movl output_len(%ebp), %eax
79	addl %eax, %ebx
80	/* Add 8 bytes for every 32K input block */
81	shrl $12, %eax
82	addl %eax, %ebx
83	/* Add 32K + 18 bytes of extra slack */
84	addl $(32768 + 18), %ebx
85	/* Align on a 4K boundary */
86	addl $4095, %ebx
87	andl $~4095, %ebx
88
89/* Copy the compressed kernel to the end of our buffer
90 * where decompression in place becomes safe.
91 */
92	pushl %esi
93	leal _end(%ebp), %esi
94	leal _end(%ebx), %edi
95	movl $(_end - startup_32), %ecx
96	std
97	rep
98	movsb
99	cld
100	popl %esi
101
102/* Compute the kernel start address.
103 */
104#ifdef CONFIG_RELOCATABLE
105	addl    $(CONFIG_PHYSICAL_ALIGN - 1), %ebp
106	andl    $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebp
107#else
108	movl	$LOAD_PHYSICAL_ADDR, %ebp
109#endif
110
111/*
112 * Jump to the relocated address.
113 */
114	leal relocated(%ebx), %eax
115	jmp *%eax
116.section ".text"
117relocated:
118
119/*
120 * Clear BSS
121 */
122	xorl %eax,%eax
123	leal _edata(%ebx),%edi
124	leal _end(%ebx), %ecx
125	subl %edi,%ecx
126	cld
127	rep
128	stosb
129
130/*
131 * Setup the stack for the decompressor
132 */
133	leal boot_stack_end(%ebx), %esp
134
135/*
136 * Do the decompression, and jump to the new kernel..
137 */
138	movl output_len(%ebx), %eax
139	pushl %eax
140	pushl %ebp	# output address
141	movl input_len(%ebx), %eax
142	pushl %eax	# input_len
143	leal input_data(%ebx), %eax
144	pushl %eax	# input_data
145	leal boot_heap(%ebx), %eax
146	pushl %eax	# heap area as third argument
147	pushl %esi	# real mode pointer as second arg
148	call decompress_kernel
149	addl $20, %esp
150	popl %ecx
151
152#if CONFIG_RELOCATABLE
153/* Find the address of the relocations.
154 */
155	movl %ebp, %edi
156	addl %ecx, %edi
157
158/* Calculate the delta between where vmlinux was compiled to run
159 * and where it was actually loaded.
160 */
161	movl %ebp, %ebx
162	subl $LOAD_PHYSICAL_ADDR, %ebx
163	jz   2f		/* Nothing to be done if loaded at compiled addr. */
164/*
165 * Process relocations.
166 */
167
1681:	subl $4, %edi
169	movl 0(%edi), %ecx
170	testl %ecx, %ecx
171	jz 2f
172	addl %ebx, -__PAGE_OFFSET(%ebx, %ecx)
173	jmp 1b
1742:
175#endif
176
177/*
178 * Jump to the decompressed kernel.
179 */
180	xorl %ebx,%ebx
181	jmp *%ebp
182
183.bss
184/* Stack and heap for uncompression */
185.balign 4
186boot_heap:
187	.fill BOOT_HEAP_SIZE, 1, 0
188boot_stack:
189	.fill BOOT_STACK_SIZE, 1, 0
190boot_stack_end:
191