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/init.h>
27 #include <linux/linkage.h>
28 #include <asm/segment.h>
29 #include <asm/page_types.h>
31 #include <asm/asm-offsets.h>
35 #ifdef CONFIG_EFI_STUB
39 * We don't need the return address, so set up the stack so
40 * efi_main() can find its arguments.
58 movl %ecx, BP_code32_start(%eax)
69 /* EFI init failed, so hang. */
73 movl BP_code32_start(%esi), %eax
74 leal preferred_addr(%eax), %eax
81 * Test KEEP_SEGMENTS flag to see if the bootloader is asking
82 * us to not reload segments
84 testb $(1<<6), BP_loadflags(%esi)
97 * Calculate the delta between where we were compiled to run
98 * at and where we were actually loaded at. This can only be done
99 * with a short local call on x86. Nothing else will tell us what
100 * address we are running at. The reserved chunk of the real-mode
101 * data at 0x1e4 (defined as a scratch field) are used as the stack
102 * for this calculation. Only 4 bytes are needed.
104 leal (BP_scratch+4)(%esi), %esp
110 * %ebp contains the address we are loaded at by the boot loader and %ebx
111 * contains the address where we should move the kernel image temporarily
112 * for safe in-place decompression.
115 #ifdef CONFIG_RELOCATABLE
117 movl BP_kernel_alignment(%esi), %eax
122 cmpl $LOAD_PHYSICAL_ADDR, %ebx
125 movl $LOAD_PHYSICAL_ADDR, %ebx
128 /* Target address to relocate to for decompression */
129 addl $z_extract_offset, %ebx
131 /* Set up the stack */
132 leal boot_stack_end(%ebx), %esp
139 * Copy the compressed kernel to the end of our buffer
140 * where decompression in place becomes safe.
143 leal (_bss-4)(%ebp), %esi
144 leal (_bss-4)(%ebx), %edi
145 movl $(_bss - startup_32), %ecx
153 * Jump to the relocated address.
155 leal relocated(%ebx), %eax
163 * Clear BSS (stack is currently empty)
166 leal _bss(%ebx), %edi
167 leal _ebss(%ebx), %ecx
175 leal _got(%ebx), %edx
176 leal _egot(%ebx), %ecx
186 * Do the decompression, and jump to the new kernel..
188 /* push arguments for decompress_kernel: */
189 pushl $z_run_size /* size of kernel with .bss and .brk */
190 pushl $z_output_len /* decompressed length, end of relocs */
191 leal z_extract_offset_negative(%ebx), %ebp
192 pushl %ebp /* output address */
193 pushl $z_input_len /* input_len */
194 leal input_data(%ebx), %eax
195 pushl %eax /* input_data */
196 leal boot_heap(%ebx), %eax
197 pushl %eax /* heap area */
198 pushl %esi /* real mode pointer */
199 call decompress_kernel /* returns kernel location in %eax */
203 * Jump to the decompressed kernel.
209 * Stack and heap for uncompression
214 .fill BOOT_HEAP_SIZE, 1, 0
216 .fill BOOT_STACK_SIZE, 1, 0