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/pgtable_types.h> 31#include <asm/page_types.h> 32#include <asm/boot.h> 33#include <asm/msr.h> 34#include <asm/processor-flags.h> 35#include <asm/asm-offsets.h> 36 37 __HEAD 38 .code32 39ENTRY(startup_32) 40 cld 41 /* 42 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 43 * us to not reload segments 44 */ 45 testb $(1<<6), BP_loadflags(%esi) 46 jnz 1f 47 48 cli 49 movl $(__KERNEL_DS), %eax 50 movl %eax, %ds 51 movl %eax, %es 52 movl %eax, %ss 531: 54 55/* 56 * Calculate the delta between where we were compiled to run 57 * at and where we were actually loaded at. This can only be done 58 * with a short local call on x86. Nothing else will tell us what 59 * address we are running at. The reserved chunk of the real-mode 60 * data at 0x1e4 (defined as a scratch field) are used as the stack 61 * for this calculation. Only 4 bytes are needed. 62 */ 63 leal (BP_scratch+4)(%esi), %esp 64 call 1f 651: popl %ebp 66 subl $1b, %ebp 67 68/* setup a stack and make sure cpu supports long mode. */ 69 movl $boot_stack_end, %eax 70 addl %ebp, %eax 71 movl %eax, %esp 72 73 call verify_cpu 74 testl %eax, %eax 75 jnz no_longmode 76 77/* 78 * Compute the delta between where we were compiled to run at 79 * and where the code will actually run at. 80 * 81 * %ebp contains the address we are loaded at by the boot loader and %ebx 82 * contains the address where we should move the kernel image temporarily 83 * for safe in-place decompression. 84 */ 85 86#ifdef CONFIG_RELOCATABLE 87 movl %ebp, %ebx 88 movl BP_kernel_alignment(%esi), %eax 89 decl %eax 90 addl %eax, %ebx 91 notl %eax 92 andl %eax, %ebx 93#else 94 movl $LOAD_PHYSICAL_ADDR, %ebx 95#endif 96 97 /* Target address to relocate to for decompression */ 98 addl $z_extract_offset, %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 movl $(X86_CR4_PAE), %eax 111 movl %eax, %cr4 112 113 /* 114 * Build early 4G boot pagetable 115 */ 116 /* Initialize Page tables to 0 */ 117 leal pgtable(%ebx), %edi 118 xorl %eax, %eax 119 movl $((4096*6)/4), %ecx 120 rep stosl 121 122 /* Build Level 4 */ 123 leal pgtable + 0(%ebx), %edi 124 leal 0x1007 (%edi), %eax 125 movl %eax, 0(%edi) 126 127 /* Build Level 3 */ 128 leal pgtable + 0x1000(%ebx), %edi 129 leal 0x1007(%edi), %eax 130 movl $4, %ecx 1311: movl %eax, 0x00(%edi) 132 addl $0x00001000, %eax 133 addl $8, %edi 134 decl %ecx 135 jnz 1b 136 137 /* Build Level 2 */ 138 leal pgtable + 0x2000(%ebx), %edi 139 movl $0x00000183, %eax 140 movl $2048, %ecx 1411: movl %eax, 0(%edi) 142 addl $0x00200000, %eax 143 addl $8, %edi 144 decl %ecx 145 jnz 1b 146 147 /* Enable the boot page tables */ 148 leal pgtable(%ebx), %eax 149 movl %eax, %cr3 150 151 /* Enable Long mode in EFER (Extended Feature Enable Register) */ 152 movl $MSR_EFER, %ecx 153 rdmsr 154 btsl $_EFER_LME, %eax 155 wrmsr 156 157 /* 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.S" 186 187 /* 188 * Be careful here startup_64 needs to be at a predictable 189 * address so I can export it in an ELF header. Bootloaders 190 * should look at the ELF header to find this address, as 191 * it may change in the future. 192 */ 193 .code64 194 .org 0x200 195ENTRY(startup_64) 196 /* 197 * We come here either from startup_32 or directly from a 198 * 64bit bootloader. If we come here from a bootloader we depend on 199 * an identity mapped page table being provied that maps our 200 * entire text+data+bss and hopefully all of memory. 201 */ 202#ifdef CONFIG_EFI_STUB 203 /* 204 * The entry point for the PE/COFF executable is efi_pe_entry, so 205 * only legacy boot loaders will execute this jmp. 206 */ 207 jmp preferred_addr 208 209ENTRY(efi_pe_entry) 210 mov %rcx, %rdi 211 mov %rdx, %rsi 212 pushq %rdi 213 pushq %rsi 214 call make_boot_params 215 cmpq $0,%rax 216 je 1f 217 mov %rax, %rdx 218 popq %rsi 219 popq %rdi 220 221ENTRY(efi_stub_entry) 222 call efi_main 223 movq %rax,%rsi 224 cmpq $0,%rax 225 jne 2f 2261: 227 /* EFI init failed, so hang. */ 228 hlt 229 jmp 1b 2302: 231 call 3f 2323: 233 popq %rax 234 subq $3b, %rax 235 subq BP_pref_address(%rsi), %rax 236 add BP_code32_start(%esi), %eax 237 leaq preferred_addr(%rax), %rax 238 jmp *%rax 239 240preferred_addr: 241#endif 242 243 /* Setup data segments. */ 244 xorl %eax, %eax 245 movl %eax, %ds 246 movl %eax, %es 247 movl %eax, %ss 248 movl %eax, %fs 249 movl %eax, %gs 250 lldt %ax 251 movl $0x20, %eax 252 ltr %ax 253 254 /* 255 * Compute the decompressed kernel start address. It is where 256 * we were loaded at aligned to a 2M boundary. %rbp contains the 257 * decompressed kernel start address. 258 * 259 * If it is a relocatable kernel then decompress and run the kernel 260 * from load address aligned to 2MB addr, otherwise decompress and 261 * run the kernel from LOAD_PHYSICAL_ADDR 262 * 263 * We cannot rely on the calculation done in 32-bit mode, since we 264 * may have been invoked via the 64-bit entry point. 265 */ 266 267 /* Start with the delta to where the kernel will run at. */ 268#ifdef CONFIG_RELOCATABLE 269 leaq startup_32(%rip) /* - $startup_32 */, %rbp 270 movl BP_kernel_alignment(%rsi), %eax 271 decl %eax 272 addq %rax, %rbp 273 notq %rax 274 andq %rax, %rbp 275#else 276 movq $LOAD_PHYSICAL_ADDR, %rbp 277#endif 278 279 /* Target address to relocate to for decompression */ 280 leaq z_extract_offset(%rbp), %rbx 281 282 /* Set up the stack */ 283 leaq boot_stack_end(%rbx), %rsp 284 285 /* Zero EFLAGS */ 286 pushq $0 287 popfq 288 289/* 290 * Copy the compressed kernel to the end of our buffer 291 * where decompression in place becomes safe. 292 */ 293 pushq %rsi 294 leaq (_bss-8)(%rip), %rsi 295 leaq (_bss-8)(%rbx), %rdi 296 movq $_bss /* - $startup_32 */, %rcx 297 shrq $3, %rcx 298 std 299 rep movsq 300 cld 301 popq %rsi 302 303/* 304 * Jump to the relocated address. 305 */ 306 leaq relocated(%rbx), %rax 307 jmp *%rax 308 309 .text 310relocated: 311 312/* 313 * Clear BSS (stack is currently empty) 314 */ 315 xorl %eax, %eax 316 leaq _bss(%rip), %rdi 317 leaq _ebss(%rip), %rcx 318 subq %rdi, %rcx 319 shrq $3, %rcx 320 rep stosq 321 322/* 323 * Adjust our own GOT 324 */ 325 leaq _got(%rip), %rdx 326 leaq _egot(%rip), %rcx 3271: 328 cmpq %rcx, %rdx 329 jae 2f 330 addq %rbx, (%rdx) 331 addq $8, %rdx 332 jmp 1b 3332: 334 335/* 336 * Do the decompression, and jump to the new kernel.. 337 */ 338 pushq %rsi /* Save the real mode argument */ 339 movq %rsi, %rdi /* real mode address */ 340 leaq boot_heap(%rip), %rsi /* malloc area for uncompression */ 341 leaq input_data(%rip), %rdx /* input_data */ 342 movl $z_input_len, %ecx /* input_len */ 343 movq %rbp, %r8 /* output target address */ 344 call decompress_kernel 345 popq %rsi 346 347/* 348 * Jump to the decompressed kernel. 349 */ 350 jmp *%rbp 351 352 .data 353gdt: 354 .word gdt_end - gdt 355 .long gdt 356 .word 0 357 .quad 0x0000000000000000 /* NULL descriptor */ 358 .quad 0x00af9a000000ffff /* __KERNEL_CS */ 359 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 360 .quad 0x0080890000000000 /* TS descriptor */ 361 .quad 0x0000000000000000 /* TS continued */ 362gdt_end: 363 364/* 365 * Stack and heap for uncompression 366 */ 367 .bss 368 .balign 4 369boot_heap: 370 .fill BOOT_HEAP_SIZE, 1, 0 371boot_stack: 372 .fill BOOT_STACK_SIZE, 1, 0 373boot_stack_end: 374 375/* 376 * Space for page tables (not in .bss so not zeroed) 377 */ 378 .section ".pgtable","a",@nobits 379 .balign 4096 380pgtable: 381 .fill 6*4096, 1, 0 382