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>
28 #include <asm/page_types.h>
30 #include <asm/asm-offsets.h>
32 .section ".text.head","ax",@progbits
36 * Test KEEP_SEGMENTS flag to see if the bootloader is asking
37 * us to not reload segments
39 testb $(1<<6), BP_loadflags(%esi)
52 * Calculate the delta between where we were compiled to run
53 * at and where we were actually loaded at. This can only be done
54 * with a short local call on x86. Nothing else will tell us what
55 * address we are running at. The reserved chunk of the real-mode
56 * data at 0x1e4 (defined as a scratch field) are used as the stack
57 * for this calculation. Only 4 bytes are needed.
59 leal (BP_scratch+4)(%esi), %esp
65 * %ebp contains the address we are loaded at by the boot loader and %ebx
66 * contains the address where we should move the kernel image temporarily
67 * for safe in-place decompression.
70 #ifdef CONFIG_RELOCATABLE
72 addl $(CONFIG_PHYSICAL_ALIGN - 1), %ebx
73 andl $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebx
75 movl $LOAD_PHYSICAL_ADDR, %ebx
78 /* Replace the compressed data size with the uncompressed size */
79 subl input_len(%ebp), %ebx
80 movl output_len(%ebp), %eax
82 /* Add 8 bytes for every 32K input block */
85 /* Add 32K + 18 bytes of extra slack */
86 addl $(32768 + 18), %ebx
87 /* Align on a 4K boundary */
91 /* Set up the stack */
92 leal boot_stack_end(%ebx), %esp
99 * Copy the compressed kernel to the end of our buffer
100 * where decompression in place becomes safe.
103 leal (_bss-4)(%ebp), %esi
104 leal (_bss-4)(%ebx), %edi
105 movl $(_bss - startup_32), %ecx
113 * Compute the kernel start address.
115 #ifdef CONFIG_RELOCATABLE
116 addl $(CONFIG_PHYSICAL_ALIGN - 1), %ebp
117 andl $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebp
119 movl $LOAD_PHYSICAL_ADDR, %ebp
123 * Jump to the relocated address.
125 leal relocated(%ebx), %eax
133 * Clear BSS (stack is currently empty)
136 leal _bss(%ebx), %edi
137 leal _ebss(%ebx), %ecx
143 * Do the decompression, and jump to the new kernel..
145 movl output_len(%ebx), %eax
147 /* push arguments for decompress_kernel: */
148 pushl %ebp /* output address */
149 movl input_len(%ebx), %eax
150 pushl %eax /* input_len */
151 leal input_data(%ebx), %eax
152 pushl %eax /* input_data */
153 leal boot_heap(%ebx), %eax
154 pushl %eax /* heap area */
155 pushl %esi /* real mode pointer */
156 call decompress_kernel
160 #if CONFIG_RELOCATABLE
162 * Find the address of the relocations.
168 * Calculate the delta between where vmlinux was compiled to run
169 * and where it was actually loaded.
172 subl $LOAD_PHYSICAL_ADDR, %ebx
173 jz 2f /* Nothing to be done if loaded at compiled addr. */
175 * Process relocations.
182 addl %ebx, -__PAGE_OFFSET(%ebx, %ecx)
188 * Jump to the decompressed kernel.
194 * Stack and heap for uncompression
199 .fill BOOT_HEAP_SIZE, 1, 0
201 .fill BOOT_STACK_SIZE, 1, 0