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/msr.h> 32#include <asm/asm-offsets.h> 33 34.section ".text.head" 35 .code32 36 .globl startup_32 37 38startup_32: 39 cld 40 /* test KEEP_SEGMENTS flag to see if the bootloader is asking 41 * us to not reload segments */ 42 testb $(1<<6), BP_loadflags(%esi) 43 jnz 1f 44 45 cli 46 movl $(__KERNEL_DS), %eax 47 movl %eax, %ds 48 movl %eax, %es 49 movl %eax, %ss 501: 51 52/* Calculate the delta between where we were compiled to run 53 * at and where we were actually loaded at. This can only be done 54 * with a short local call on x86. Nothing else will tell us what 55 * address we are running at. The reserved chunk of the real-mode 56 * data at 0x1e4 (defined as a scratch field) are used as the stack 57 * for this calculation. Only 4 bytes are needed. 58 */ 59 leal (0x1e4+4)(%esi), %esp 60 call 1f 611: popl %ebp 62 subl $1b, %ebp 63 64/* setup a stack and make sure cpu supports long mode. */ 65 movl $user_stack_end, %eax 66 addl %ebp, %eax 67 movl %eax, %esp 68 69 call verify_cpu 70 testl %eax, %eax 71 jnz no_longmode 72 73/* Compute the delta between where we were compiled to run at 74 * and where the code will actually run at. 75 */ 76/* %ebp contains the address we are loaded at by the boot loader and %ebx 77 * contains the address where we should move the kernel image temporarily 78 * for safe in-place decompression. 79 */ 80 81#ifdef CONFIG_RELOCATABLE 82 movl %ebp, %ebx 83 addl $(PMD_PAGE_SIZE -1), %ebx 84 andl $PMD_PAGE_MASK, %ebx 85#else 86 movl $CONFIG_PHYSICAL_START, %ebx 87#endif 88 89 /* Replace the compressed data size with the uncompressed size */ 90 subl input_len(%ebp), %ebx 91 movl output_len(%ebp), %eax 92 addl %eax, %ebx 93 /* Add 8 bytes for every 32K input block */ 94 shrl $12, %eax 95 addl %eax, %ebx 96 /* Add 32K + 18 bytes of extra slack and align on a 4K boundary */ 97 addl $(32768 + 18 + 4095), %ebx 98 andl $~4095, %ebx 99 100/* 101 * Prepare for entering 64 bit mode 102 */ 103 104 /* Load new GDT with the 64bit segments using 32bit descriptor */ 105 leal gdt(%ebp), %eax 106 movl %eax, gdt+2(%ebp) 107 lgdt gdt(%ebp) 108 109 /* Enable PAE mode */ 110 xorl %eax, %eax 111 orl $(1 << 5), %eax 112 movl %eax, %cr4 113 114 /* 115 * Build early 4G boot pagetable 116 */ 117 /* Initialize Page tables to 0*/ 118 leal pgtable(%ebx), %edi 119 xorl %eax, %eax 120 movl $((4096*6)/4), %ecx 121 rep stosl 122 123 /* Build Level 4 */ 124 leal pgtable + 0(%ebx), %edi 125 leal 0x1007 (%edi), %eax 126 movl %eax, 0(%edi) 127 128 /* Build Level 3 */ 129 leal pgtable + 0x1000(%ebx), %edi 130 leal 0x1007(%edi), %eax 131 movl $4, %ecx 1321: movl %eax, 0x00(%edi) 133 addl $0x00001000, %eax 134 addl $8, %edi 135 decl %ecx 136 jnz 1b 137 138 /* Build Level 2 */ 139 leal pgtable + 0x2000(%ebx), %edi 140 movl $0x00000183, %eax 141 movl $2048, %ecx 1421: movl %eax, 0(%edi) 143 addl $0x00200000, %eax 144 addl $8, %edi 145 decl %ecx 146 jnz 1b 147 148 /* Enable the boot page tables */ 149 leal pgtable(%ebx), %eax 150 movl %eax, %cr3 151 152 /* Enable Long mode in EFER (Extended Feature Enable Register) */ 153 movl $MSR_EFER, %ecx 154 rdmsr 155 btsl $_EFER_LME, %eax 156 wrmsr 157 158 /* Setup for the jump to 64bit mode 159 * 160 * When the jump is performend we will be in long mode but 161 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1 162 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use 163 * the new gdt/idt that has __KERNEL_CS with CS.L = 1. 164 * We place all of the values on our mini stack so lret can 165 * used to perform that far jump. 166 */ 167 pushl $__KERNEL_CS 168 leal startup_64(%ebp), %eax 169 pushl %eax 170 171 /* Enter paged protected Mode, activating Long Mode */ 172 movl $0x80000001, %eax /* Enable Paging and Protected mode */ 173 movl %eax, %cr0 174 175 /* Jump from 32bit compatibility mode into 64bit mode. */ 176 lret 177 178no_longmode: 179 /* This isn't an x86-64 CPU so hang */ 1801: 181 hlt 182 jmp 1b 183 184#include "../../kernel/verify_cpu_64.S" 185 186 /* Be careful here startup_64 needs to be at a predictable 187 * address so I can export it in an ELF header. Bootloaders 188 * should look at the ELF header to find this address, as 189 * it may change in the future. 190 */ 191 .code64 192 .org 0x200 193ENTRY(startup_64) 194 /* We come here either from startup_32 or directly from a 195 * 64bit bootloader. If we come here from a bootloader we depend on 196 * an identity mapped page table being provied that maps our 197 * entire text+data+bss and hopefully all of memory. 198 */ 199 200 /* Setup data segments. */ 201 xorl %eax, %eax 202 movl %eax, %ds 203 movl %eax, %es 204 movl %eax, %ss 205 movl %eax, %fs 206 movl %eax, %gs 207 lldt %ax 208 movl $0x20, %eax 209 ltr %ax 210 211 /* Compute the decompressed kernel start address. It is where 212 * we were loaded at aligned to a 2M boundary. %rbp contains the 213 * decompressed kernel start address. 214 * 215 * If it is a relocatable kernel then decompress and run the kernel 216 * from load address aligned to 2MB addr, otherwise decompress and 217 * run the kernel from CONFIG_PHYSICAL_START 218 */ 219 220 /* Start with the delta to where the kernel will run at. */ 221#ifdef CONFIG_RELOCATABLE 222 leaq startup_32(%rip) /* - $startup_32 */, %rbp 223 addq $(PMD_PAGE_SIZE - 1), %rbp 224 andq $PMD_PAGE_MASK, %rbp 225 movq %rbp, %rbx 226#else 227 movq $CONFIG_PHYSICAL_START, %rbp 228 movq %rbp, %rbx 229#endif 230 231 /* Replace the compressed data size with the uncompressed size */ 232 movl input_len(%rip), %eax 233 subq %rax, %rbx 234 movl output_len(%rip), %eax 235 addq %rax, %rbx 236 /* Add 8 bytes for every 32K input block */ 237 shrq $12, %rax 238 addq %rax, %rbx 239 /* Add 32K + 18 bytes of extra slack and align on a 4K boundary */ 240 addq $(32768 + 18 + 4095), %rbx 241 andq $~4095, %rbx 242 243/* Copy the compressed kernel to the end of our buffer 244 * where decompression in place becomes safe. 245 */ 246 leaq _end(%rip), %r8 247 leaq _end(%rbx), %r9 248 movq $_end /* - $startup_32 */, %rcx 2491: subq $8, %r8 250 subq $8, %r9 251 movq 0(%r8), %rax 252 movq %rax, 0(%r9) 253 subq $8, %rcx 254 jnz 1b 255 256/* 257 * Jump to the relocated address. 258 */ 259 leaq relocated(%rbx), %rax 260 jmp *%rax 261 262.section ".text" 263relocated: 264 265/* 266 * Clear BSS 267 */ 268 xorq %rax, %rax 269 leaq _edata(%rbx), %rdi 270 leaq _end(%rbx), %rcx 271 subq %rdi, %rcx 272 cld 273 rep 274 stosb 275 276 /* Setup the stack */ 277 leaq user_stack_end(%rip), %rsp 278 279 /* zero EFLAGS after setting rsp */ 280 pushq $0 281 popfq 282 283/* 284 * Do the decompression, and jump to the new kernel.. 285 */ 286 pushq %rsi # Save the real mode argument 287 movq %rsi, %rdi # real mode address 288 leaq _heap(%rip), %rsi # _heap 289 leaq input_data(%rip), %rdx # input_data 290 movl input_len(%rip), %eax 291 movq %rax, %rcx # input_len 292 movq %rbp, %r8 # output 293 call decompress_kernel 294 popq %rsi 295 296 297/* 298 * Jump to the decompressed kernel. 299 */ 300 jmp *%rbp 301 302 .data 303gdt: 304 .word gdt_end - gdt 305 .long gdt 306 .word 0 307 .quad 0x0000000000000000 /* NULL descriptor */ 308 .quad 0x00af9a000000ffff /* __KERNEL_CS */ 309 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 310 .quad 0x0080890000000000 /* TS descriptor */ 311 .quad 0x0000000000000000 /* TS continued */ 312gdt_end: 313 .bss 314/* Stack for uncompression */ 315 .balign 4 316user_stack: 317 .fill 4096,4,0 318user_stack_end: 319