4 * Copyright (C) 1991, 1992, 1993 Linus Torvalds
8 * head.S contains the 32-bit startup code.
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]
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
22 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
26 #include <linux/linkage.h>
27 #include <asm/segment.h>
30 #include <asm/asm-offsets.h>
32 .section ".text.head","ax",@progbits
36 /* check to see if KEEP_SEGMENTS flag is meaningful */
37 cmpw $0x207, BP_version(%esi)
40 /* test KEEP_SEGMENTS flag to see if the bootloader is asking
41 * us to not reload segments */
42 testb $(1<<6), BP_loadflags(%esi)
46 movl $(__BOOT_DS),%eax
55 /* Calculate the delta between where we were compiled to run
56 * at and where we were actually loaded at. This can only be done
57 * with a short local call on x86. Nothing else will tell us what
58 * address we are running at. The reserved chunk of the real-mode
59 * data at 0x1e4 (defined as a scratch field) are used as the stack
60 * for this calculation. Only 4 bytes are needed.
62 leal (0x1e4+4)(%esi), %esp
67 /* %ebp contains the address we are loaded at by the boot loader and %ebx
68 * contains the address where we should move the kernel image temporarily
69 * for safe in-place decompression.
72 #ifdef CONFIG_RELOCATABLE
74 addl $(CONFIG_PHYSICAL_ALIGN - 1), %ebx
75 andl $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebx
77 movl $LOAD_PHYSICAL_ADDR, %ebx
80 /* Replace the compressed data size with the uncompressed size */
81 subl input_len(%ebp), %ebx
82 movl output_len(%ebp), %eax
84 /* Add 8 bytes for every 32K input block */
87 /* Add 32K + 18 bytes of extra slack */
88 addl $(32768 + 18), %ebx
89 /* Align on a 4K boundary */
93 /* Copy the compressed kernel to the end of our buffer
94 * where decompression in place becomes safe.
99 movl $(_end - startup_32), %ecx
106 /* Compute the kernel start address.
108 #ifdef CONFIG_RELOCATABLE
109 addl $(CONFIG_PHYSICAL_ALIGN - 1), %ebp
110 andl $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebp
112 movl $LOAD_PHYSICAL_ADDR, %ebp
116 * Jump to the relocated address.
118 leal relocated(%ebx), %eax
127 leal _edata(%ebx),%edi
128 leal _end(%ebx), %ecx
135 * Setup the stack for the decompressor
137 leal stack_end(%ebx), %esp
140 * Do the decompression, and jump to the new kernel..
142 movl output_len(%ebx), %eax
144 pushl %ebp # output address
145 movl input_len(%ebx), %eax
146 pushl %eax # input_len
147 leal input_data(%ebx), %eax
148 pushl %eax # input_data
149 leal _end(%ebx), %eax
150 pushl %eax # end of the image as third argument
151 pushl %esi # real mode pointer as second arg
152 call decompress_kernel
156 #if CONFIG_RELOCATABLE
157 /* Find the address of the relocations.
162 /* Calculate the delta between where vmlinux was compiled to run
163 * and where it was actually loaded.
166 subl $LOAD_PHYSICAL_ADDR, %ebx
167 jz 2f /* Nothing to be done if loaded at compiled addr. */
169 * Process relocations.
176 addl %ebx, -__PAGE_OFFSET(%ebx, %ecx)
182 * Jump to the decompressed kernel.