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_types.h> 30#include <asm/page_types.h> 31#include <asm/boot.h> 32#include <asm/msr.h> 33#include <asm/processor-flags.h> 34#include <asm/asm-offsets.h> 35 36.section ".text.head" 37 .code32 38ENTRY(startup_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 $boot_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 $(X86_CR4_PAE), %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 $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */ 173 movl %eax, %cr0 174 175 /* Jump from 32bit compatibility mode into 64bit mode. */ 176 lret 177ENDPROC(startup_32) 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 * 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: 313 314.bss 315/* Stack and heap for uncompression */ 316.balign 4 317boot_heap: 318 .fill BOOT_HEAP_SIZE, 1, 0 319boot_stack: 320 .fill BOOT_STACK_SIZE, 1, 0 321boot_stack_end: 322