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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 | /* SPDX-License-Identifier: GPL-2.0 */ /* * linux/boot/head.S * * Copyright (C) 1991, 1992, 1993 Linus Torvalds */ /* * head.S contains the 32-bit startup code. * * NOTE!!! Startup happens at absolute address 0x00001000, which is also where * the page directory will exist. The startup code will be overwritten by * the page directory. [According to comments etc elsewhere on a compressed * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC] * * Page 0 is deliberately kept safe, since System Management Mode code in * laptops may need to access the BIOS data stored there. This is also * useful for future device drivers that either access the BIOS via VM86 * mode. */ /* * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996 */ .text #include <linux/init.h> #include <linux/linkage.h> #include <asm/segment.h> #include <asm/page_types.h> #include <asm/boot.h> #include <asm/asm-offsets.h> #include <asm/bootparam.h> /* * These symbols needed to be marked as .hidden to prevent the BFD linker from * generating R_386_32 (rather than R_386_RELATIVE) relocations for them when * the 32-bit compressed kernel is linked as PIE. This is no longer necessary, * but it doesn't hurt to keep them .hidden. */ .hidden _bss .hidden _ebss .hidden _end __HEAD SYM_FUNC_START(startup_32) cld cli /* * Calculate the delta between where we were compiled to run * at and where we were actually loaded at. This can only be done * with a short local call on x86. Nothing else will tell us what * address we are running at. The reserved chunk of the real-mode * data at 0x1e4 (defined as a scratch field) are used as the stack * for this calculation. Only 4 bytes are needed. */ leal (BP_scratch+4)(%esi), %esp call 1f 1: popl %edx addl $_GLOBAL_OFFSET_TABLE_+(.-1b), %edx /* Load new GDT */ leal gdt@GOTOFF(%edx), %eax movl %eax, 2(%eax) lgdt (%eax) /* Load segment registers with our descriptors */ movl $__BOOT_DS, %eax movl %eax, %ds movl %eax, %es movl %eax, %fs movl %eax, %gs movl %eax, %ss /* * %edx contains the address we are loaded at by the boot loader (plus the * offset to the GOT). The below code calculates %ebx to be the address where * we should move the kernel image temporarily for safe in-place decompression * (again, plus the offset to the GOT). * * %ebp is calculated to be the address that the kernel will be decompressed to. */ #ifdef CONFIG_RELOCATABLE leal startup_32@GOTOFF(%edx), %ebx movl BP_kernel_alignment(%esi), %eax decl %eax addl %eax, %ebx notl %eax andl %eax, %ebx cmpl $LOAD_PHYSICAL_ADDR, %ebx jae 1f #endif movl $LOAD_PHYSICAL_ADDR, %ebx 1: movl %ebx, %ebp // Save the output address for later /* Target address to relocate to for decompression */ addl BP_init_size(%esi), %ebx subl $_end@GOTOFF, %ebx /* Set up the stack */ leal boot_stack_end@GOTOFF(%ebx), %esp /* Zero EFLAGS */ pushl $0 popfl /* * Copy the compressed kernel to the end of our buffer * where decompression in place becomes safe. */ pushl %esi leal (_bss@GOTOFF-4)(%edx), %esi leal (_bss@GOTOFF-4)(%ebx), %edi movl $(_bss - startup_32), %ecx shrl $2, %ecx std rep movsl cld popl %esi /* * The GDT may get overwritten either during the copy we just did or * during extract_kernel below. To avoid any issues, repoint the GDTR * to the new copy of the GDT. */ leal gdt@GOTOFF(%ebx), %eax movl %eax, 2(%eax) lgdt (%eax) /* * Jump to the relocated address. */ leal .Lrelocated@GOTOFF(%ebx), %eax jmp *%eax SYM_FUNC_END(startup_32) .text SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) /* * Clear BSS (stack is currently empty) */ xorl %eax, %eax leal _bss@GOTOFF(%ebx), %edi leal _ebss@GOTOFF(%ebx), %ecx subl %edi, %ecx shrl $2, %ecx rep stosl /* * Do the extraction, and jump to the new kernel.. */ /* push arguments for extract_kernel: */ pushl %ebp /* output address */ pushl %esi /* real mode pointer */ call extract_kernel /* returns kernel entry point in %eax */ addl $24, %esp /* * Jump to the extracted kernel. */ xorl %ebx, %ebx jmp *%eax SYM_FUNC_END(.Lrelocated) .data .balign 8 SYM_DATA_START_LOCAL(gdt) .word gdt_end - gdt - 1 .long 0 .word 0 .quad 0x0000000000000000 /* Reserved */ .quad 0x00cf9a000000ffff /* __KERNEL_CS */ .quad 0x00cf92000000ffff /* __KERNEL_DS */ SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end) /* * Stack and heap for uncompression */ .bss .balign 4 boot_stack: .fill BOOT_STACK_SIZE, 1, 0 boot_stack_end: |