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 * The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X 37 * relocation to get the symbol address in PIC. When the compressed x86 38 * kernel isn't built as PIC, the linker optimizes R_386_GOT32X 39 * relocations to their fixed symbol addresses. However, when the 40 * compressed x86 kernel is loaded at a different address, it leads 41 * to the following load failure: 42 * 43 * Failed to allocate space for phdrs 44 * 45 * during the decompression stage. 46 * 47 * If the compressed x86 kernel is relocatable at run-time, it should be 48 * compiled with -fPIE, instead of -fPIC, if possible and should be built as 49 * Position Independent Executable (PIE) so that linker won't optimize 50 * R_386_GOT32X relocation to its fixed symbol address. Older 51 * linkers generate R_386_32 relocations against locally defined symbols, 52 * _bss, _ebss, _got, _egot and _end, in PIE. It isn't wrong, just less 53 * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle 54 * R_386_32 relocations when relocating the kernel. To generate 55 * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and _end as 56 * hidden: 57 */ 58 .hidden _bss 59 .hidden _ebss 60 .hidden _got 61 .hidden _egot 62 .hidden _end 63 64 __HEAD 65ENTRY(startup_32) 66 cld 67 /* 68 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 69 * us to not reload segments 70 */ 71 testb $KEEP_SEGMENTS, BP_loadflags(%esi) 72 jnz 1f 73 74 cli 75 movl $__BOOT_DS, %eax 76 movl %eax, %ds 77 movl %eax, %es 78 movl %eax, %fs 79 movl %eax, %gs 80 movl %eax, %ss 811: 82 83/* 84 * Calculate the delta between where we were compiled to run 85 * at and where we were actually loaded at. This can only be done 86 * with a short local call on x86. Nothing else will tell us what 87 * address we are running at. The reserved chunk of the real-mode 88 * data at 0x1e4 (defined as a scratch field) are used as the stack 89 * for this calculation. Only 4 bytes are needed. 90 */ 91 leal (BP_scratch+4)(%esi), %esp 92 call 1f 931: popl %ebp 94 subl $1b, %ebp 95 96/* 97 * %ebp contains the address we are loaded at by the boot loader and %ebx 98 * contains the address where we should move the kernel image temporarily 99 * for safe in-place decompression. 100 */ 101 102#ifdef CONFIG_RELOCATABLE 103 movl %ebp, %ebx 104 movl BP_kernel_alignment(%esi), %eax 105 decl %eax 106 addl %eax, %ebx 107 notl %eax 108 andl %eax, %ebx 109 cmpl $LOAD_PHYSICAL_ADDR, %ebx 110 jae 1f 111#endif 112 movl $LOAD_PHYSICAL_ADDR, %ebx 1131: 114 115 /* Target address to relocate to for decompression */ 116 movl BP_init_size(%esi), %eax 117 subl $_end, %eax 118 addl %eax, %ebx 119 120 /* Set up the stack */ 121 leal boot_stack_end(%ebx), %esp 122 123 /* Zero EFLAGS */ 124 pushl $0 125 popfl 126 127/* 128 * Copy the compressed kernel to the end of our buffer 129 * where decompression in place becomes safe. 130 */ 131 pushl %esi 132 leal (_bss-4)(%ebp), %esi 133 leal (_bss-4)(%ebx), %edi 134 movl $(_bss - startup_32), %ecx 135 shrl $2, %ecx 136 std 137 rep movsl 138 cld 139 popl %esi 140 141/* 142 * Jump to the relocated address. 143 */ 144 leal relocated(%ebx), %eax 145 jmp *%eax 146ENDPROC(startup_32) 147 148#ifdef CONFIG_EFI_STUB 149/* 150 * We don't need the return address, so set up the stack so efi_main() can find 151 * its arguments. 152 */ 153ENTRY(efi_pe_entry) 154 add $0x4, %esp 155 156 call 1f 1571: popl %esi 158 subl $1b, %esi 159 160 popl %ecx 161 movl %ecx, efi32_config(%esi) /* Handle */ 162 popl %ecx 163 movl %ecx, efi32_config+8(%esi) /* EFI System table pointer */ 164 165 /* Relocate efi_config->call() */ 166 leal efi32_config(%esi), %eax 167 add %esi, 40(%eax) 168 pushl %eax 169 170 call make_boot_params 171 cmpl $0, %eax 172 je fail 173 movl %esi, BP_code32_start(%eax) 174 popl %ecx 175 pushl %eax 176 pushl %ecx 177 jmp 2f /* Skip efi_config initialization */ 178ENDPROC(efi_pe_entry) 179 180ENTRY(efi32_stub_entry) 181 add $0x4, %esp 182 popl %ecx 183 popl %edx 184 185 call 1f 1861: popl %esi 187 subl $1b, %esi 188 189 movl %ecx, efi32_config(%esi) /* Handle */ 190 movl %edx, efi32_config+8(%esi) /* EFI System table pointer */ 191 192 /* Relocate efi_config->call() */ 193 leal efi32_config(%esi), %eax 194 add %esi, 40(%eax) 195 pushl %eax 1962: 197 call efi_main 198 cmpl $0, %eax 199 movl %eax, %esi 200 jne 2f 201fail: 202 /* EFI init failed, so hang. */ 203 hlt 204 jmp fail 2052: 206 movl BP_code32_start(%esi), %eax 207 leal startup_32(%eax), %eax 208 jmp *%eax 209ENDPROC(efi32_stub_entry) 210#endif 211 212 .text 213relocated: 214 215/* 216 * Clear BSS (stack is currently empty) 217 */ 218 xorl %eax, %eax 219 leal _bss(%ebx), %edi 220 leal _ebss(%ebx), %ecx 221 subl %edi, %ecx 222 shrl $2, %ecx 223 rep stosl 224 225/* 226 * Adjust our own GOT 227 */ 228 leal _got(%ebx), %edx 229 leal _egot(%ebx), %ecx 2301: 231 cmpl %ecx, %edx 232 jae 2f 233 addl %ebx, (%edx) 234 addl $4, %edx 235 jmp 1b 2362: 237 238/* 239 * Do the extraction, and jump to the new kernel.. 240 */ 241 /* push arguments for extract_kernel: */ 242 pushl $z_output_len /* decompressed length, end of relocs */ 243 244 movl BP_init_size(%esi), %eax 245 subl $_end, %eax 246 movl %ebx, %ebp 247 subl %eax, %ebp 248 pushl %ebp /* output address */ 249 250 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 */ 257 addl $24, %esp 258 259/* 260 * Jump to the extracted kernel. 261 */ 262 xorl %ebx, %ebx 263 jmp *%eax 264 265#ifdef CONFIG_EFI_STUB 266 .data 267efi32_config: 268 .fill 5,8,0 269 .long efi_call_phys 270 .long 0 271 .byte 0 272#endif 273 274/* 275 * Stack and heap for uncompression 276 */ 277 .bss 278 .balign 4 279boot_heap: 280 .fill BOOT_HEAP_SIZE, 1, 0 281boot_stack: 282 .fill BOOT_STACK_SIZE, 1, 0 283boot_stack_end: 284