1/* SPDX-License-Identifier: GPL-2.0 */ 2/* 3 * linux/boot/head.S 4 * 5 * Copyright (C) 1991, 1992, 1993 Linus Torvalds 6 */ 7 8/* 9 * head.S contains the 32-bit startup code. 10 * 11 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where 12 * the page directory will exist. The startup code will be overwritten by 13 * the page directory. [According to comments etc elsewhere on a compressed 14 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC] 15 * 16 * Page 0 is deliberately kept safe, since System Management Mode code in 17 * laptops may need to access the BIOS data stored there. This is also 18 * useful for future device drivers that either access the BIOS via VM86 19 * mode. 20 */ 21 22/* 23 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996 24 */ 25 .text 26 27#include <linux/init.h> 28#include <linux/linkage.h> 29#include <asm/segment.h> 30#include <asm/page_types.h> 31#include <asm/boot.h> 32#include <asm/asm-offsets.h> 33#include <asm/bootparam.h> 34 35/* 36 * These symbols needed to be marked as .hidden to prevent the BFD linker from 37 * generating R_386_32 (rather than R_386_RELATIVE) relocations for them when 38 * the 32-bit compressed kernel is linked as PIE. This is no longer necessary, 39 * but it doesn't hurt to keep them .hidden. 40 */ 41 .hidden _bss 42 .hidden _ebss 43 .hidden _end 44 45 __HEAD 46SYM_FUNC_START(startup_32) 47 cld 48 cli 49 50/* 51 * Calculate the delta between where we were compiled to run 52 * at and where we were actually loaded at. This can only be done 53 * with a short local call on x86. Nothing else will tell us what 54 * address we are running at. The reserved chunk of the real-mode 55 * data at 0x1e4 (defined as a scratch field) are used as the stack 56 * for this calculation. Only 4 bytes are needed. 57 */ 58 leal (BP_scratch+4)(%esi), %esp 59 call 1f 601: popl %edx 61 addl $_GLOBAL_OFFSET_TABLE_+(.-1b), %edx 62 63 /* Load new GDT */ 64 leal gdt@GOTOFF(%edx), %eax 65 movl %eax, 2(%eax) 66 lgdt (%eax) 67 68 /* Load segment registers with our descriptors */ 69 movl $__BOOT_DS, %eax 70 movl %eax, %ds 71 movl %eax, %es 72 movl %eax, %fs 73 movl %eax, %gs 74 movl %eax, %ss 75 76/* 77 * %edx contains the address we are loaded at by the boot loader (plus the 78 * offset to the GOT). The below code calculates %ebx to be the address where 79 * we should move the kernel image temporarily for safe in-place decompression 80 * (again, plus the offset to the GOT). 81 * 82 * %ebp is calculated to be the address that the kernel will be decompressed to. 83 */ 84 85#ifdef CONFIG_RELOCATABLE 86 leal startup_32@GOTOFF(%edx), %ebx 87 88#ifdef CONFIG_EFI_STUB 89/* 90 * If we were loaded via the EFI LoadImage service, startup_32() will be at an 91 * offset to the start of the space allocated for the image. efi_pe_entry() will 92 * set up image_offset to tell us where the image actually starts, so that we 93 * can use the full available buffer. 94 * image_offset = startup_32 - image_base 95 * Otherwise image_offset will be zero and has no effect on the calculations. 96 */ 97 subl image_offset@GOTOFF(%edx), %ebx 98#endif 99 100 movl BP_kernel_alignment(%esi), %eax 101 decl %eax 102 addl %eax, %ebx 103 notl %eax 104 andl %eax, %ebx 105 cmpl $LOAD_PHYSICAL_ADDR, %ebx 106 jae 1f 107#endif 108 movl $LOAD_PHYSICAL_ADDR, %ebx 1091: 110 111 movl %ebx, %ebp // Save the output address for later 112 /* Target address to relocate to for decompression */ 113 addl BP_init_size(%esi), %ebx 114 subl $_end@GOTOFF, %ebx 115 116 /* Set up the stack */ 117 leal boot_stack_end@GOTOFF(%ebx), %esp 118 119 /* Zero EFLAGS */ 120 pushl $0 121 popfl 122 123/* 124 * Copy the compressed kernel to the end of our buffer 125 * where decompression in place becomes safe. 126 */ 127 pushl %esi 128 leal (_bss@GOTOFF-4)(%edx), %esi 129 leal (_bss@GOTOFF-4)(%ebx), %edi 130 movl $(_bss - startup_32), %ecx 131 shrl $2, %ecx 132 std 133 rep movsl 134 cld 135 popl %esi 136 137 /* 138 * The GDT may get overwritten either during the copy we just did or 139 * during extract_kernel below. To avoid any issues, repoint the GDTR 140 * to the new copy of the GDT. 141 */ 142 leal gdt@GOTOFF(%ebx), %eax 143 movl %eax, 2(%eax) 144 lgdt (%eax) 145 146/* 147 * Jump to the relocated address. 148 */ 149 leal .Lrelocated@GOTOFF(%ebx), %eax 150 jmp *%eax 151SYM_FUNC_END(startup_32) 152 153#ifdef CONFIG_EFI_STUB 154SYM_FUNC_START(efi32_stub_entry) 155 add $0x4, %esp 156 movl 8(%esp), %esi /* save boot_params pointer */ 157 call efi_main 158 /* efi_main returns the possibly relocated address of startup_32 */ 159 jmp *%eax 160SYM_FUNC_END(efi32_stub_entry) 161SYM_FUNC_ALIAS(efi_stub_entry, efi32_stub_entry) 162#endif 163 164 .text 165SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 166 167/* 168 * Clear BSS (stack is currently empty) 169 */ 170 xorl %eax, %eax 171 leal _bss@GOTOFF(%ebx), %edi 172 leal _ebss@GOTOFF(%ebx), %ecx 173 subl %edi, %ecx 174 shrl $2, %ecx 175 rep stosl 176 177/* 178 * Do the extraction, and jump to the new kernel.. 179 */ 180 /* push arguments for extract_kernel: */ 181 182 pushl output_len@GOTOFF(%ebx) /* decompressed length, end of relocs */ 183 pushl %ebp /* output address */ 184 pushl input_len@GOTOFF(%ebx) /* input_len */ 185 leal input_data@GOTOFF(%ebx), %eax 186 pushl %eax /* input_data */ 187 leal boot_heap@GOTOFF(%ebx), %eax 188 pushl %eax /* heap area */ 189 pushl %esi /* real mode pointer */ 190 call extract_kernel /* returns kernel location in %eax */ 191 addl $24, %esp 192 193/* 194 * Jump to the extracted kernel. 195 */ 196 xorl %ebx, %ebx 197 jmp *%eax 198SYM_FUNC_END(.Lrelocated) 199 200 .data 201 .balign 8 202SYM_DATA_START_LOCAL(gdt) 203 .word gdt_end - gdt - 1 204 .long 0 205 .word 0 206 .quad 0x0000000000000000 /* Reserved */ 207 .quad 0x00cf9a000000ffff /* __KERNEL_CS */ 208 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 209SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end) 210 211#ifdef CONFIG_EFI_STUB 212SYM_DATA(image_offset, .long 0) 213#endif 214 215/* 216 * Stack and heap for uncompression 217 */ 218 .bss 219 .balign 4 220boot_heap: 221 .fill BOOT_HEAP_SIZE, 1, 0 222boot_stack: 223 .fill BOOT_STACK_SIZE, 1, 0 224boot_stack_end: 225