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 46 SYM_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 60 1: 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 movl BP_kernel_alignment(%esi), %eax 88 decl %eax 89 addl %eax, %ebx 90 notl %eax 91 andl %eax, %ebx 92 cmpl $LOAD_PHYSICAL_ADDR, %ebx 93 jae 1f 94 #endif 95 movl $LOAD_PHYSICAL_ADDR, %ebx 96 1: 97 98 movl %ebx, %ebp // Save the output address for later 99 /* Target address to relocate to for decompression */ 100 addl BP_init_size(%esi), %ebx 101 subl $_end@GOTOFF, %ebx 102 103 /* Set up the stack */ 104 leal boot_stack_end@GOTOFF(%ebx), %esp 105 106 /* Zero EFLAGS */ 107 pushl $0 108 popfl 109 110 /* 111 * Copy the compressed kernel to the end of our buffer 112 * where decompression in place becomes safe. 113 */ 114 pushl %esi 115 leal (_bss@GOTOFF-4)(%edx), %esi 116 leal (_bss@GOTOFF-4)(%ebx), %edi 117 movl $(_bss - startup_32), %ecx 118 shrl $2, %ecx 119 std 120 rep movsl 121 cld 122 popl %esi 123 124 /* 125 * The GDT may get overwritten either during the copy we just did or 126 * during extract_kernel below. To avoid any issues, repoint the GDTR 127 * to the new copy of the GDT. 128 */ 129 leal gdt@GOTOFF(%ebx), %eax 130 movl %eax, 2(%eax) 131 lgdt (%eax) 132 133 /* 134 * Jump to the relocated address. 135 */ 136 leal .Lrelocated@GOTOFF(%ebx), %eax 137 jmp *%eax 138 SYM_FUNC_END(startup_32) 139 140 .text 141 SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 142 143 /* 144 * Clear BSS (stack is currently empty) 145 */ 146 xorl %eax, %eax 147 leal _bss@GOTOFF(%ebx), %edi 148 leal _ebss@GOTOFF(%ebx), %ecx 149 subl %edi, %ecx 150 shrl $2, %ecx 151 rep stosl 152 153 /* 154 * Do the extraction, and jump to the new kernel.. 155 */ 156 /* push arguments for extract_kernel: */ 157 158 pushl %ebp /* output address */ 159 pushl %esi /* real mode pointer */ 160 call extract_kernel /* returns kernel entry point in %eax */ 161 addl $24, %esp 162 163 /* 164 * Jump to the extracted kernel. 165 */ 166 xorl %ebx, %ebx 167 jmp *%eax 168 SYM_FUNC_END(.Lrelocated) 169 170 .data 171 .balign 8 172 SYM_DATA_START_LOCAL(gdt) 173 .word gdt_end - gdt - 1 174 .long 0 175 .word 0 176 .quad 0x0000000000000000 /* Reserved */ 177 .quad 0x00cf9a000000ffff /* __KERNEL_CS */ 178 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 179 SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end) 180 181 /* 182 * Stack and heap for uncompression 183 */ 184 .bss 185 .balign 4 186 boot_stack: 187 .fill BOOT_STACK_SIZE, 1, 0 188 boot_stack_end:
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