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 65SYM_FUNC_START(startup_32) 66 cld 67 cli 68 69/* 70 * Calculate the delta between where we were compiled to run 71 * at and where we were actually loaded at. This can only be done 72 * with a short local call on x86. Nothing else will tell us what 73 * address we are running at. The reserved chunk of the real-mode 74 * data at 0x1e4 (defined as a scratch field) are used as the stack 75 * for this calculation. Only 4 bytes are needed. 76 */ 77 leal (BP_scratch+4)(%esi), %esp 78 call 1f 791: popl %edx 80 subl $1b, %edx 81 82 /* Load new GDT */ 83 leal gdt(%edx), %eax 84 movl %eax, 2(%eax) 85 lgdt (%eax) 86 87 /* Load segment registers with our descriptors */ 88 movl $__BOOT_DS, %eax 89 movl %eax, %ds 90 movl %eax, %es 91 movl %eax, %fs 92 movl %eax, %gs 93 movl %eax, %ss 94 95/* 96 * %edx 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. %ebp contains the address that the kernel 99 * will be decompressed to. 100 */ 101 102#ifdef CONFIG_RELOCATABLE 103 movl %edx, %ebx 104 105#ifdef CONFIG_EFI_STUB 106/* 107 * If we were loaded via the EFI LoadImage service, startup_32() will be at an 108 * offset to the start of the space allocated for the image. efi_pe_entry() will 109 * set up image_offset to tell us where the image actually starts, so that we 110 * can use the full available buffer. 111 * image_offset = startup_32 - image_base 112 * Otherwise image_offset will be zero and has no effect on the calculations. 113 */ 114 subl image_offset(%edx), %ebx 115#endif 116 117 movl BP_kernel_alignment(%esi), %eax 118 decl %eax 119 addl %eax, %ebx 120 notl %eax 121 andl %eax, %ebx 122 cmpl $LOAD_PHYSICAL_ADDR, %ebx 123 jae 1f 124#endif 125 movl $LOAD_PHYSICAL_ADDR, %ebx 1261: 127 128 movl %ebx, %ebp // Save the output address for later 129 /* Target address to relocate to for decompression */ 130 addl BP_init_size(%esi), %ebx 131 subl $_end, %ebx 132 133 /* Set up the stack */ 134 leal boot_stack_end(%ebx), %esp 135 136 /* Zero EFLAGS */ 137 pushl $0 138 popfl 139 140/* 141 * Copy the compressed kernel to the end of our buffer 142 * where decompression in place becomes safe. 143 */ 144 pushl %esi 145 leal (_bss-4)(%edx), %esi 146 leal (_bss-4)(%ebx), %edi 147 movl $(_bss - startup_32), %ecx 148 shrl $2, %ecx 149 std 150 rep movsl 151 cld 152 popl %esi 153 154 /* 155 * The GDT may get overwritten either during the copy we just did or 156 * during extract_kernel below. To avoid any issues, repoint the GDTR 157 * to the new copy of the GDT. 158 */ 159 leal gdt(%ebx), %eax 160 movl %eax, 2(%eax) 161 lgdt (%eax) 162 163/* 164 * Jump to the relocated address. 165 */ 166 leal .Lrelocated(%ebx), %eax 167 jmp *%eax 168SYM_FUNC_END(startup_32) 169 170#ifdef CONFIG_EFI_STUB 171SYM_FUNC_START(efi32_stub_entry) 172SYM_FUNC_START_ALIAS(efi_stub_entry) 173 add $0x4, %esp 174 movl 8(%esp), %esi /* save boot_params pointer */ 175 call efi_main 176 leal startup_32(%eax), %eax 177 jmp *%eax 178SYM_FUNC_END(efi32_stub_entry) 179SYM_FUNC_END_ALIAS(efi_stub_entry) 180#endif 181 182 .text 183SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 184 185/* 186 * Clear BSS (stack is currently empty) 187 */ 188 xorl %eax, %eax 189 leal _bss(%ebx), %edi 190 leal _ebss(%ebx), %ecx 191 subl %edi, %ecx 192 shrl $2, %ecx 193 rep stosl 194 195/* 196 * Adjust our own GOT 197 */ 198 leal _got(%ebx), %edx 199 leal _egot(%ebx), %ecx 2001: 201 cmpl %ecx, %edx 202 jae 2f 203 addl %ebx, (%edx) 204 addl $4, %edx 205 jmp 1b 2062: 207 208/* 209 * Do the extraction, and jump to the new kernel.. 210 */ 211 /* push arguments for extract_kernel: */ 212 pushl $z_output_len /* decompressed length, end of relocs */ 213 214 pushl %ebp /* output address */ 215 216 pushl $z_input_len /* input_len */ 217 leal input_data(%ebx), %eax 218 pushl %eax /* input_data */ 219 leal boot_heap(%ebx), %eax 220 pushl %eax /* heap area */ 221 pushl %esi /* real mode pointer */ 222 call extract_kernel /* returns kernel location in %eax */ 223 addl $24, %esp 224 225/* 226 * Jump to the extracted kernel. 227 */ 228 xorl %ebx, %ebx 229 jmp *%eax 230SYM_FUNC_END(.Lrelocated) 231 232 .data 233 .balign 8 234SYM_DATA_START_LOCAL(gdt) 235 .word gdt_end - gdt - 1 236 .long 0 237 .word 0 238 .quad 0x0000000000000000 /* Reserved */ 239 .quad 0x00cf9a000000ffff /* __KERNEL_CS */ 240 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 241SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end) 242 243#ifdef CONFIG_EFI_STUB 244SYM_DATA(image_offset, .long 0) 245#endif 246 247/* 248 * Stack and heap for uncompression 249 */ 250 .bss 251 .balign 4 252boot_heap: 253 .fill BOOT_HEAP_SIZE, 1, 0 254boot_stack: 255 .fill BOOT_STACK_SIZE, 1, 0 256boot_stack_end: 257