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.
62 /* EFI init failed, so hang. */
70 subl BP_pref_address(%esi), %eax
71 add BP_code32_start(%esi), %eax
72 leal preferred_addr(%eax), %eax
79 * Test KEEP_SEGMENTS flag to see if the bootloader is asking
80 * us to not reload segments
82 testb $(1<<6), BP_loadflags(%esi)
95 * Calculate the delta between where we were compiled to run
96 * at and where we were actually loaded at. This can only be done
97 * with a short local call on x86. Nothing else will tell us what
98 * address we are running at. The reserved chunk of the real-mode
99 * data at 0x1e4 (defined as a scratch field) are used as the stack
100 * for this calculation. Only 4 bytes are needed.
102 leal (BP_scratch+4)(%esi), %esp
108 * %ebp contains the address we are loaded at by the boot loader and %ebx
109 * contains the address where we should move the kernel image temporarily
110 * for safe in-place decompression.
113 #ifdef CONFIG_RELOCATABLE
115 movl BP_kernel_alignment(%esi), %eax
121 movl $LOAD_PHYSICAL_ADDR, %ebx
124 /* Target address to relocate to for decompression */
125 addl $z_extract_offset, %ebx
127 /* Set up the stack */
128 leal boot_stack_end(%ebx), %esp
135 * Copy the compressed kernel to the end of our buffer
136 * where decompression in place becomes safe.
139 leal (_bss-4)(%ebp), %esi
140 leal (_bss-4)(%ebx), %edi
141 movl $(_bss - startup_32), %ecx
149 * Jump to the relocated address.
151 leal relocated(%ebx), %eax
159 * Clear BSS (stack is currently empty)
162 leal _bss(%ebx), %edi
163 leal _ebss(%ebx), %ecx
171 leal _got(%ebx), %edx
172 leal _egot(%ebx), %ecx
182 * Do the decompression, and jump to the new kernel..
184 leal z_extract_offset_negative(%ebx), %ebp
185 /* push arguments for decompress_kernel: */
186 pushl %ebp /* output address */
187 pushl $z_input_len /* input_len */
188 leal input_data(%ebx), %eax
189 pushl %eax /* input_data */
190 leal boot_heap(%ebx), %eax
191 pushl %eax /* heap area */
192 pushl %esi /* real mode pointer */
193 call decompress_kernel
196 #if CONFIG_RELOCATABLE
198 * Find the address of the relocations.
200 leal z_output_len(%ebp), %edi
203 * Calculate the delta between where vmlinux was compiled to run
204 * and where it was actually loaded.
207 subl $LOAD_PHYSICAL_ADDR, %ebx
208 jz 2f /* Nothing to be done if loaded at compiled addr. */
210 * Process relocations.
217 addl %ebx, -__PAGE_OFFSET(%ebx, %ecx)
223 * Jump to the decompressed kernel.
229 * Stack and heap for uncompression
234 .fill BOOT_HEAP_SIZE, 1, 0
236 .fill BOOT_STACK_SIZE, 1, 0