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 and _egot, 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 and _egot as 56 * hidden: 57 */ 58 .hidden _bss 59 .hidden _ebss 60 .hidden _got 61 .hidden _egot 62 63 __HEAD 64SYM_FUNC_START(startup_32) 65 cld 66 /* 67 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 68 * us to not reload segments 69 */ 70 testb $KEEP_SEGMENTS, BP_loadflags(%esi) 71 jnz 1f 72 73 cli 74 movl $__BOOT_DS, %eax 75 movl %eax, %ds 76 movl %eax, %es 77 movl %eax, %fs 78 movl %eax, %gs 79 movl %eax, %ss 801: 81 82/* 83 * Calculate the delta between where we were compiled to run 84 * at and where we were actually loaded at. This can only be done 85 * with a short local call on x86. Nothing else will tell us what 86 * address we are running at. The reserved chunk of the real-mode 87 * data at 0x1e4 (defined as a scratch field) are used as the stack 88 * for this calculation. Only 4 bytes are needed. 89 */ 90 leal (BP_scratch+4)(%esi), %esp 91 call 1f 921: popl %ebp 93 subl $1b, %ebp 94 95/* 96 * %ebp contains the address we are loaded at by the boot loader and %ebx 97 * contains the address where we should move the kernel image temporarily 98 * for safe in-place decompression. 99 */ 100 101#ifdef CONFIG_RELOCATABLE 102 movl %ebp, %ebx 103 movl BP_kernel_alignment(%esi), %eax 104 decl %eax 105 addl %eax, %ebx 106 notl %eax 107 andl %eax, %ebx 108 cmpl $LOAD_PHYSICAL_ADDR, %ebx 109 jge 1f 110#endif 111 movl $LOAD_PHYSICAL_ADDR, %ebx 1121: 113 114 /* Target address to relocate to for decompression */ 115 movl BP_init_size(%esi), %eax 116 subl $_end, %eax 117 addl %eax, %ebx 118 119 /* Set up the stack */ 120 leal boot_stack_end(%ebx), %esp 121 122 /* Zero EFLAGS */ 123 pushl $0 124 popfl 125 126/* 127 * Copy the compressed kernel to the end of our buffer 128 * where decompression in place becomes safe. 129 */ 130 pushl %esi 131 leal (_bss-4)(%ebp), %esi 132 leal (_bss-4)(%ebx), %edi 133 movl $(_bss - startup_32), %ecx 134 shrl $2, %ecx 135 std 136 rep movsl 137 cld 138 popl %esi 139 140/* 141 * Jump to the relocated address. 142 */ 143 leal .Lrelocated(%ebx), %eax 144 jmp *%eax 145SYM_FUNC_END(startup_32) 146 147#ifdef CONFIG_EFI_STUB 148SYM_FUNC_START(efi32_stub_entry) 149SYM_FUNC_START_ALIAS(efi_stub_entry) 150 add $0x4, %esp 151 call efi_main 152 movl %eax, %esi 153 movl BP_code32_start(%esi), %eax 154 leal startup_32(%eax), %eax 155 jmp *%eax 156SYM_FUNC_END(efi32_stub_entry) 157SYM_FUNC_END_ALIAS(efi_stub_entry) 158#endif 159 160 .text 161SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 162 163/* 164 * Clear BSS (stack is currently empty) 165 */ 166 xorl %eax, %eax 167 leal _bss(%ebx), %edi 168 leal _ebss(%ebx), %ecx 169 subl %edi, %ecx 170 shrl $2, %ecx 171 rep stosl 172 173/* 174 * Adjust our own GOT 175 */ 176 leal _got(%ebx), %edx 177 leal _egot(%ebx), %ecx 1781: 179 cmpl %ecx, %edx 180 jae 2f 181 addl %ebx, (%edx) 182 addl $4, %edx 183 jmp 1b 1842: 185 186/* 187 * Do the extraction, and jump to the new kernel.. 188 */ 189 /* push arguments for extract_kernel: */ 190 pushl $z_output_len /* decompressed length, end of relocs */ 191 192 leal _end(%ebx), %eax 193 subl BP_init_size(%esi), %eax 194 pushl %eax /* output address */ 195 196 pushl $z_input_len /* input_len */ 197 leal input_data(%ebx), %eax 198 pushl %eax /* input_data */ 199 leal boot_heap(%ebx), %eax 200 pushl %eax /* heap area */ 201 pushl %esi /* real mode pointer */ 202 call extract_kernel /* returns kernel location in %eax */ 203 addl $24, %esp 204 205/* 206 * Jump to the extracted kernel. 207 */ 208 xorl %ebx, %ebx 209 jmp *%eax 210SYM_FUNC_END(.Lrelocated) 211 212/* 213 * Stack and heap for uncompression 214 */ 215 .bss 216 .balign 4 217boot_heap: 218 .fill BOOT_HEAP_SIZE, 1, 0 219boot_stack: 220 .fill BOOT_STACK_SIZE, 1, 0 221boot_stack_end: 222