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>
32 #include <asm/bootparam.h>
35 * The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X
36 * relocation to get the symbol address in PIC. When the compressed x86
37 * kernel isn't built as PIC, the linker optimizes R_386_GOT32X
38 * relocations to their fixed symbol addresses. However, when the
39 * compressed x86 kernel is loaded at a different address, it leads
40 * to the following load failure:
42 * Failed to allocate space for phdrs
44 * during the decompression stage.
46 * If the compressed x86 kernel is relocatable at run-time, it should be
47 * compiled with -fPIE, instead of -fPIC, if possible and should be built as
48 * Position Independent Executable (PIE) so that linker won't optimize
49 * R_386_GOT32X relocation to its fixed symbol address. Older
50 * linkers generate R_386_32 relocations against locally defined symbols,
51 * _bss, _ebss, _got, _egot and _end, in PIE. It isn't wrong, just less
52 * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle
53 * R_386_32 relocations when relocating the kernel. To generate
54 * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and _end as
65 #ifdef CONFIG_EFI_STUB
69 * We don't need the return address, so set up the stack so
70 * efi_main() can find its arguments.
80 movl %ecx, efi32_config(%esi) /* Handle */
82 movl %ecx, efi32_config+8(%esi) /* EFI System table pointer */
84 /* Relocate efi_config->call() */
85 leal efi32_config(%esi), %eax
92 movl %esi, BP_code32_start(%eax)
96 jmp 2f /* Skip efi_config initialization */
98 ENTRY(efi32_stub_entry)
107 movl %ecx, efi32_config(%esi) /* Handle */
108 movl %edx, efi32_config+8(%esi) /* EFI System table pointer */
110 /* Relocate efi_config->call() */
111 leal efi32_config(%esi), %eax
120 /* EFI init failed, so hang. */
124 movl BP_code32_start(%esi), %eax
125 leal preferred_addr(%eax), %eax
132 * Test KEEP_SEGMENTS flag to see if the bootloader is asking
133 * us to not reload segments
135 testb $KEEP_SEGMENTS, BP_loadflags(%esi)
139 movl $__BOOT_DS, %eax
148 * Calculate the delta between where we were compiled to run
149 * at and where we were actually loaded at. This can only be done
150 * with a short local call on x86. Nothing else will tell us what
151 * address we are running at. The reserved chunk of the real-mode
152 * data at 0x1e4 (defined as a scratch field) are used as the stack
153 * for this calculation. Only 4 bytes are needed.
155 leal (BP_scratch+4)(%esi), %esp
161 * %ebp contains the address we are loaded at by the boot loader and %ebx
162 * contains the address where we should move the kernel image temporarily
163 * for safe in-place decompression.
166 #ifdef CONFIG_RELOCATABLE
168 movl BP_kernel_alignment(%esi), %eax
173 cmpl $LOAD_PHYSICAL_ADDR, %ebx
176 movl $LOAD_PHYSICAL_ADDR, %ebx
179 /* Target address to relocate to for decompression */
180 movl BP_init_size(%esi), %eax
184 /* Set up the stack */
185 leal boot_stack_end(%ebx), %esp
192 * Copy the compressed kernel to the end of our buffer
193 * where decompression in place becomes safe.
196 leal (_bss-4)(%ebp), %esi
197 leal (_bss-4)(%ebx), %edi
198 movl $(_bss - startup_32), %ecx
206 * Jump to the relocated address.
208 leal relocated(%ebx), %eax
216 * Clear BSS (stack is currently empty)
219 leal _bss(%ebx), %edi
220 leal _ebss(%ebx), %ecx
228 leal _got(%ebx), %edx
229 leal _egot(%ebx), %ecx
239 * Do the extraction, and jump to the new kernel..
241 /* push arguments for extract_kernel: */
242 pushl $z_output_len /* decompressed length, end of relocs */
244 movl BP_init_size(%esi), %eax
248 pushl %ebp /* output address */
250 pushl $z_input_len /* input_len */
251 leal input_data(%ebx), %eax
252 pushl %eax /* input_data */
253 leal boot_heap(%ebx), %eax
254 pushl %eax /* heap area */
255 pushl %esi /* real mode pointer */
256 call extract_kernel /* returns kernel location in %eax */
260 * Jump to the extracted kernel.
265 #ifdef CONFIG_EFI_STUB
275 * Stack and heap for uncompression
280 .fill BOOT_HEAP_SIZE, 1, 0
282 .fill BOOT_STACK_SIZE, 1, 0