1/* 2 * linux/boot/head.S 3 * 4 * Copyright (C) 1991, 1992, 1993 Linus Torvalds 5 */ 6 7/* 8 * head.S contains the 32-bit startup code. 9 * 10 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where 11 * the page directory will exist. The startup code will be overwritten by 12 * the page directory. [According to comments etc elsewhere on a compressed 13 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC] 14 * 15 * Page 0 is deliberately kept safe, since System Management Mode code in 16 * laptops may need to access the BIOS data stored there. This is also 17 * useful for future device drivers that either access the BIOS via VM86 18 * mode. 19 */ 20 21/* 22 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996 23 */ 24.code32 25.text 26 27#include <linux/linkage.h> 28#include <asm/segment.h> 29#include <asm/pgtable.h> 30#include <asm/page.h> 31#include <asm/boot.h> 32#include <asm/msr.h> 33#include <asm/asm-offsets.h> 34 35.section ".text.head" 36 .code32 37 .globl startup_32 38 39startup_32: 40 cld 41 /* test KEEP_SEGMENTS flag to see if the bootloader is asking 42 * us to not reload segments */ 43 testb $(1<<6), BP_loadflags(%esi) 44 jnz 1f 45 46 cli 47 movl $(__KERNEL_DS), %eax 48 movl %eax, %ds 49 movl %eax, %es 50 movl %eax, %ss 511: 52 53/* Calculate the delta between where we were compiled to run 54 * at and where we were actually loaded at. This can only be done 55 * with a short local call on x86. Nothing else will tell us what 56 * address we are running at. The reserved chunk of the real-mode 57 * data at 0x1e4 (defined as a scratch field) are used as the stack 58 * for this calculation. Only 4 bytes are needed. 59 */ 60 leal (0x1e4+4)(%esi), %esp 61 call 1f 621: popl %ebp 63 subl $1b, %ebp 64 65/* setup a stack and make sure cpu supports long mode. */ 66 movl $boot_stack_end, %eax 67 addl %ebp, %eax 68 movl %eax, %esp 69 70 call verify_cpu 71 testl %eax, %eax 72 jnz no_longmode 73 74/* Compute the delta between where we were compiled to run at 75 * and where the code will actually run at. 76 */ 77/* %ebp contains the address we are loaded at by the boot loader and %ebx 78 * contains the address where we should move the kernel image temporarily 79 * for safe in-place decompression. 80 */ 81 82#ifdef CONFIG_RELOCATABLE 83 movl %ebp, %ebx 84 addl $(PMD_PAGE_SIZE -1), %ebx 85 andl $PMD_PAGE_MASK, %ebx 86#else 87 movl $CONFIG_PHYSICAL_START, %ebx 88#endif 89 90 /* Replace the compressed data size with the uncompressed size */ 91 subl input_len(%ebp), %ebx 92 movl output_len(%ebp), %eax 93 addl %eax, %ebx 94 /* Add 8 bytes for every 32K input block */ 95 shrl $12, %eax 96 addl %eax, %ebx 97 /* Add 32K + 18 bytes of extra slack and align on a 4K boundary */ 98 addl $(32768 + 18 + 4095), %ebx 99 andl $~4095, %ebx 100 101/* 102 * Prepare for entering 64 bit mode 103 */ 104 105 /* Load new GDT with the 64bit segments using 32bit descriptor */ 106 leal gdt(%ebp), %eax 107 movl %eax, gdt+2(%ebp) 108 lgdt gdt(%ebp) 109 110 /* Enable PAE mode */ 111 xorl %eax, %eax 112 orl $(1 << 5), %eax 113 movl %eax, %cr4 114 115 /* 116 * Build early 4G boot pagetable 117 */ 118 /* Initialize Page tables to 0*/ 119 leal pgtable(%ebx), %edi 120 xorl %eax, %eax 121 movl $((4096*6)/4), %ecx 122 rep stosl 123 124 /* Build Level 4 */ 125 leal pgtable + 0(%ebx), %edi 126 leal 0x1007 (%edi), %eax 127 movl %eax, 0(%edi) 128 129 /* Build Level 3 */ 130 leal pgtable + 0x1000(%ebx), %edi 131 leal 0x1007(%edi), %eax 132 movl $4, %ecx 1331: movl %eax, 0x00(%edi) 134 addl $0x00001000, %eax 135 addl $8, %edi 136 decl %ecx 137 jnz 1b 138 139 /* Build Level 2 */ 140 leal pgtable + 0x2000(%ebx), %edi 141 movl $0x00000183, %eax 142 movl $2048, %ecx 1431: movl %eax, 0(%edi) 144 addl $0x00200000, %eax 145 addl $8, %edi 146 decl %ecx 147 jnz 1b 148 149 /* Enable the boot page tables */ 150 leal pgtable(%ebx), %eax 151 movl %eax, %cr3 152 153 /* Enable Long mode in EFER (Extended Feature Enable Register) */ 154 movl $MSR_EFER, %ecx 155 rdmsr 156 btsl $_EFER_LME, %eax 157 wrmsr 158 159 /* Setup for the jump to 64bit mode 160 * 161 * When the jump is performend we will be in long mode but 162 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1 163 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use 164 * the new gdt/idt that has __KERNEL_CS with CS.L = 1. 165 * We place all of the values on our mini stack so lret can 166 * used to perform that far jump. 167 */ 168 pushl $__KERNEL_CS 169 leal startup_64(%ebp), %eax 170 pushl %eax 171 172 /* Enter paged protected Mode, activating Long Mode */ 173 movl $0x80000001, %eax /* Enable Paging and Protected mode */ 174 movl %eax, %cr0 175 176 /* Jump from 32bit compatibility mode into 64bit mode. */ 177 lret 178 179no_longmode: 180 /* This isn't an x86-64 CPU so hang */ 1811: 182 hlt 183 jmp 1b 184 185#include "../../kernel/verify_cpu_64.S" 186 187 /* Be careful here startup_64 needs to be at a predictable 188 * address so I can export it in an ELF header. Bootloaders 189 * should look at the ELF header to find this address, as 190 * it may change in the future. 191 */ 192 .code64 193 .org 0x200 194ENTRY(startup_64) 195 /* We come here either from startup_32 or directly from a 196 * 64bit bootloader. If we come here from a bootloader we depend on 197 * an identity mapped page table being provied that maps our 198 * entire text+data+bss and hopefully all of memory. 199 */ 200 201 /* Setup data segments. */ 202 xorl %eax, %eax 203 movl %eax, %ds 204 movl %eax, %es 205 movl %eax, %ss 206 movl %eax, %fs 207 movl %eax, %gs 208 lldt %ax 209 movl $0x20, %eax 210 ltr %ax 211 212 /* Compute the decompressed kernel start address. It is where 213 * we were loaded at aligned to a 2M boundary. %rbp contains the 214 * decompressed kernel start address. 215 * 216 * If it is a relocatable kernel then decompress and run the kernel 217 * from load address aligned to 2MB addr, otherwise decompress and 218 * run the kernel from CONFIG_PHYSICAL_START 219 */ 220 221 /* Start with the delta to where the kernel will run at. */ 222#ifdef CONFIG_RELOCATABLE 223 leaq startup_32(%rip) /* - $startup_32 */, %rbp 224 addq $(PMD_PAGE_SIZE - 1), %rbp 225 andq $PMD_PAGE_MASK, %rbp 226 movq %rbp, %rbx 227#else 228 movq $CONFIG_PHYSICAL_START, %rbp 229 movq %rbp, %rbx 230#endif 231 232 /* Replace the compressed data size with the uncompressed size */ 233 movl input_len(%rip), %eax 234 subq %rax, %rbx 235 movl output_len(%rip), %eax 236 addq %rax, %rbx 237 /* Add 8 bytes for every 32K input block */ 238 shrq $12, %rax 239 addq %rax, %rbx 240 /* Add 32K + 18 bytes of extra slack and align on a 4K boundary */ 241 addq $(32768 + 18 + 4095), %rbx 242 andq $~4095, %rbx 243 244/* Copy the compressed kernel to the end of our buffer 245 * where decompression in place becomes safe. 246 */ 247 leaq _end_before_pgt(%rip), %r8 248 leaq _end_before_pgt(%rbx), %r9 249 movq $_end_before_pgt /* - $startup_32 */, %rcx 2501: subq $8, %r8 251 subq $8, %r9 252 movq 0(%r8), %rax 253 movq %rax, 0(%r9) 254 subq $8, %rcx 255 jnz 1b 256 257/* 258 * Jump to the relocated address. 259 */ 260 leaq relocated(%rbx), %rax 261 jmp *%rax 262 263.section ".text" 264relocated: 265 266/* 267 * Clear BSS 268 */ 269 xorq %rax, %rax 270 leaq _edata(%rbx), %rdi 271 leaq _end_before_pgt(%rbx), %rcx 272 subq %rdi, %rcx 273 cld 274 rep 275 stosb 276 277 /* Setup the stack */ 278 leaq boot_stack_end(%rip), %rsp 279 280 /* zero EFLAGS after setting rsp */ 281 pushq $0 282 popfq 283 284/* 285 * Do the decompression, and jump to the new kernel.. 286 */ 287 pushq %rsi # Save the real mode argument 288 movq %rsi, %rdi # real mode address 289 leaq boot_heap(%rip), %rsi # malloc area for uncompression 290 leaq input_data(%rip), %rdx # input_data 291 movl input_len(%rip), %eax 292 movq %rax, %rcx # input_len 293 movq %rbp, %r8 # output 294 call decompress_kernel 295 popq %rsi 296 297 298/* 299 * Jump to the decompressed kernel. 300 */ 301 jmp *%rbp 302 303 .data 304gdt: 305 .word gdt_end - gdt 306 .long gdt 307 .word 0 308 .quad 0x0000000000000000 /* NULL descriptor */ 309 .quad 0x00af9a000000ffff /* __KERNEL_CS */ 310 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 311 .quad 0x0080890000000000 /* TS descriptor */ 312 .quad 0x0000000000000000 /* TS continued */ 313gdt_end: 314 315.bss 316/* Stack and heap for uncompression */ 317.balign 4 318boot_heap: 319 .fill BOOT_HEAP_SIZE, 1, 0 320boot_stack: 321 .fill BOOT_STACK_SIZE, 1, 0 322boot_stack_end: 323