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/init.h> 28#include <linux/linkage.h> 29#include <asm/segment.h> 30#include <asm/boot.h> 31#include <asm/msr.h> 32#include <asm/processor-flags.h> 33#include <asm/asm-offsets.h> 34 35 __HEAD 36 .code32 37ENTRY(startup_32) 38 /* 39 * 32bit entry is 0 and it is ABI so immutable! 40 * If we come here directly from a bootloader, 41 * kernel(text+data+bss+brk) ramdisk, zero_page, command line 42 * all need to be under the 4G limit. 43 */ 44 cld 45 /* 46 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 47 * us to not reload segments 48 */ 49 testb $(1<<6), BP_loadflags(%esi) 50 jnz 1f 51 52 cli 53 movl $(__BOOT_DS), %eax 54 movl %eax, %ds 55 movl %eax, %es 56 movl %eax, %ss 571: 58 59/* 60 * Calculate the delta between where we were compiled to run 61 * at and where we were actually loaded at. This can only be done 62 * with a short local call on x86. Nothing else will tell us what 63 * address we are running at. The reserved chunk of the real-mode 64 * data at 0x1e4 (defined as a scratch field) are used as the stack 65 * for this calculation. Only 4 bytes are needed. 66 */ 67 leal (BP_scratch+4)(%esi), %esp 68 call 1f 691: popl %ebp 70 subl $1b, %ebp 71 72/* setup a stack and make sure cpu supports long mode. */ 73 movl $boot_stack_end, %eax 74 addl %ebp, %eax 75 movl %eax, %esp 76 77 call verify_cpu 78 testl %eax, %eax 79 jnz no_longmode 80 81/* 82 * Compute the delta between where we were compiled to run at 83 * and where the code will actually run at. 84 * 85 * %ebp contains the address we are loaded at by the boot loader and %ebx 86 * contains the address where we should move the kernel image temporarily 87 * for safe in-place decompression. 88 */ 89 90#ifdef CONFIG_RELOCATABLE 91 movl %ebp, %ebx 92 movl BP_kernel_alignment(%esi), %eax 93 decl %eax 94 addl %eax, %ebx 95 notl %eax 96 andl %eax, %ebx 97 cmpl $LOAD_PHYSICAL_ADDR, %ebx 98 jge 1f 99#endif 100 movl $LOAD_PHYSICAL_ADDR, %ebx 1011: 102 103 /* Target address to relocate to for decompression */ 104 addl $z_extract_offset, %ebx 105 106/* 107 * Prepare for entering 64 bit mode 108 */ 109 110 /* Load new GDT with the 64bit segments using 32bit descriptor */ 111 leal gdt(%ebp), %eax 112 movl %eax, gdt+2(%ebp) 113 lgdt gdt(%ebp) 114 115 /* Enable PAE mode */ 116 movl $(X86_CR4_PAE), %eax 117 movl %eax, %cr4 118 119 /* 120 * Build early 4G boot pagetable 121 */ 122 /* Initialize Page tables to 0 */ 123 leal pgtable(%ebx), %edi 124 xorl %eax, %eax 125 movl $((4096*6)/4), %ecx 126 rep stosl 127 128 /* Build Level 4 */ 129 leal pgtable + 0(%ebx), %edi 130 leal 0x1007 (%edi), %eax 131 movl %eax, 0(%edi) 132 133 /* Build Level 3 */ 134 leal pgtable + 0x1000(%ebx), %edi 135 leal 0x1007(%edi), %eax 136 movl $4, %ecx 1371: movl %eax, 0x00(%edi) 138 addl $0x00001000, %eax 139 addl $8, %edi 140 decl %ecx 141 jnz 1b 142 143 /* Build Level 2 */ 144 leal pgtable + 0x2000(%ebx), %edi 145 movl $0x00000183, %eax 146 movl $2048, %ecx 1471: movl %eax, 0(%edi) 148 addl $0x00200000, %eax 149 addl $8, %edi 150 decl %ecx 151 jnz 1b 152 153 /* Enable the boot page tables */ 154 leal pgtable(%ebx), %eax 155 movl %eax, %cr3 156 157 /* Enable Long mode in EFER (Extended Feature Enable Register) */ 158 movl $MSR_EFER, %ecx 159 rdmsr 160 btsl $_EFER_LME, %eax 161 wrmsr 162 163 /* After gdt is loaded */ 164 xorl %eax, %eax 165 lldt %ax 166 movl $0x20, %eax 167 ltr %ax 168 169 /* 170 * Setup for the jump to 64bit mode 171 * 172 * When the jump is performend we will be in long mode but 173 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1 174 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use 175 * the new gdt/idt that has __KERNEL_CS with CS.L = 1. 176 * We place all of the values on our mini stack so lret can 177 * used to perform that far jump. 178 */ 179 pushl $__KERNEL_CS 180 leal startup_64(%ebp), %eax 181 pushl %eax 182 183 /* Enter paged protected Mode, activating Long Mode */ 184 movl $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */ 185 movl %eax, %cr0 186 187 /* Jump from 32bit compatibility mode into 64bit mode. */ 188 lret 189ENDPROC(startup_32) 190 191 .code64 192 .org 0x200 193ENTRY(startup_64) 194 /* 195 * 64bit entry is 0x200 and it is ABI so immutable! 196 * We come here either from startup_32 or directly from a 197 * 64bit bootloader. 198 * If we come here from a bootloader, kernel(text+data+bss+brk), 199 * ramdisk, zero_page, command line could be above 4G. 200 * We depend on an identity mapped page table being provided 201 * that maps our entire kernel(text+data+bss+brk), zero page 202 * and command line. 203 */ 204#ifdef CONFIG_EFI_STUB 205 /* 206 * The entry point for the PE/COFF executable is efi_pe_entry, so 207 * only legacy boot loaders will execute this jmp. 208 */ 209 jmp preferred_addr 210 211ENTRY(efi_pe_entry) 212 mov %rcx, %rdi 213 mov %rdx, %rsi 214 pushq %rdi 215 pushq %rsi 216 call make_boot_params 217 cmpq $0,%rax 218 je 1f 219 mov %rax, %rdx 220 popq %rsi 221 popq %rdi 222 223ENTRY(efi_stub_entry) 224 call efi_main 225 movq %rax,%rsi 226 cmpq $0,%rax 227 jne 2f 2281: 229 /* EFI init failed, so hang. */ 230 hlt 231 jmp 1b 2322: 233 call 3f 2343: 235 popq %rax 236 subq $3b, %rax 237 subq BP_pref_address(%rsi), %rax 238 add BP_code32_start(%esi), %eax 239 leaq preferred_addr(%rax), %rax 240 jmp *%rax 241 242preferred_addr: 243#endif 244 245 /* Setup data segments. */ 246 xorl %eax, %eax 247 movl %eax, %ds 248 movl %eax, %es 249 movl %eax, %ss 250 movl %eax, %fs 251 movl %eax, %gs 252 253 /* 254 * Compute the decompressed kernel start address. It is where 255 * we were loaded at aligned to a 2M boundary. %rbp contains the 256 * decompressed kernel start address. 257 * 258 * If it is a relocatable kernel then decompress and run the kernel 259 * from load address aligned to 2MB addr, otherwise decompress and 260 * run the kernel from LOAD_PHYSICAL_ADDR 261 * 262 * We cannot rely on the calculation done in 32-bit mode, since we 263 * may have been invoked via the 64-bit entry point. 264 */ 265 266 /* Start with the delta to where the kernel will run at. */ 267#ifdef CONFIG_RELOCATABLE 268 leaq startup_32(%rip) /* - $startup_32 */, %rbp 269 movl BP_kernel_alignment(%rsi), %eax 270 decl %eax 271 addq %rax, %rbp 272 notq %rax 273 andq %rax, %rbp 274 cmpq $LOAD_PHYSICAL_ADDR, %rbp 275 jge 1f 276#endif 277 movq $LOAD_PHYSICAL_ADDR, %rbp 2781: 279 280 /* Target address to relocate to for decompression */ 281 leaq z_extract_offset(%rbp), %rbx 282 283 /* Set up the stack */ 284 leaq boot_stack_end(%rbx), %rsp 285 286 /* Zero EFLAGS */ 287 pushq $0 288 popfq 289 290/* 291 * Copy the compressed kernel to the end of our buffer 292 * where decompression in place becomes safe. 293 */ 294 pushq %rsi 295 leaq (_bss-8)(%rip), %rsi 296 leaq (_bss-8)(%rbx), %rdi 297 movq $_bss /* - $startup_32 */, %rcx 298 shrq $3, %rcx 299 std 300 rep movsq 301 cld 302 popq %rsi 303 304/* 305 * Jump to the relocated address. 306 */ 307 leaq relocated(%rbx), %rax 308 jmp *%rax 309 310 .text 311relocated: 312 313/* 314 * Clear BSS (stack is currently empty) 315 */ 316 xorl %eax, %eax 317 leaq _bss(%rip), %rdi 318 leaq _ebss(%rip), %rcx 319 subq %rdi, %rcx 320 shrq $3, %rcx 321 rep stosq 322 323/* 324 * Adjust our own GOT 325 */ 326 leaq _got(%rip), %rdx 327 leaq _egot(%rip), %rcx 3281: 329 cmpq %rcx, %rdx 330 jae 2f 331 addq %rbx, (%rdx) 332 addq $8, %rdx 333 jmp 1b 3342: 335 336/* 337 * Do the decompression, and jump to the new kernel.. 338 */ 339 pushq %rsi /* Save the real mode argument */ 340 movq %rsi, %rdi /* real mode address */ 341 leaq boot_heap(%rip), %rsi /* malloc area for uncompression */ 342 leaq input_data(%rip), %rdx /* input_data */ 343 movl $z_input_len, %ecx /* input_len */ 344 movq %rbp, %r8 /* output target address */ 345 movq $z_output_len, %r9 /* decompressed length */ 346 call decompress_kernel /* returns kernel location in %rax */ 347 popq %rsi 348 349/* 350 * Jump to the decompressed kernel. 351 */ 352 jmp *%rax 353 354 .code32 355no_longmode: 356 /* This isn't an x86-64 CPU so hang */ 3571: 358 hlt 359 jmp 1b 360 361#include "../../kernel/verify_cpu.S" 362 363 .data 364gdt: 365 .word gdt_end - gdt 366 .long gdt 367 .word 0 368 .quad 0x0000000000000000 /* NULL descriptor */ 369 .quad 0x00af9a000000ffff /* __KERNEL_CS */ 370 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 371 .quad 0x0080890000000000 /* TS descriptor */ 372 .quad 0x0000000000000000 /* TS continued */ 373gdt_end: 374 375/* 376 * Stack and heap for uncompression 377 */ 378 .bss 379 .balign 4 380boot_heap: 381 .fill BOOT_HEAP_SIZE, 1, 0 382boot_stack: 383 .fill BOOT_STACK_SIZE, 1, 0 384boot_stack_end: 385 386/* 387 * Space for page tables (not in .bss so not zeroed) 388 */ 389 .section ".pgtable","a",@nobits 390 .balign 4096 391pgtable: 392 .fill 6*4096, 1, 0 393