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 /* 41 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 42 * us to not reload segments 43 */ 44 testb $(1<<6), BP_loadflags(%esi) 45 jnz 1f 46 47 cli 48 movl $(__KERNEL_DS), %eax 49 movl %eax, %ds 50 movl %eax, %es 51 movl %eax, %ss 521: 53 54/* 55 * Calculate the delta between where we were compiled to run 56 * at and where we were actually loaded at. This can only be done 57 * with a short local call on x86. Nothing else will tell us what 58 * address we are running at. The reserved chunk of the real-mode 59 * data at 0x1e4 (defined as a scratch field) are used as the stack 60 * for this calculation. Only 4 bytes are needed. 61 */ 62 leal (BP_scratch+4)(%esi), %esp 63 call 1f 641: popl %ebp 65 subl $1b, %ebp 66 67/* setup a stack and make sure cpu supports long mode. */ 68 movl $boot_stack_end, %eax 69 addl %ebp, %eax 70 movl %eax, %esp 71 72 call verify_cpu 73 testl %eax, %eax 74 jnz no_longmode 75 76/* 77 * Compute the delta between where we were compiled to run at 78 * and where the code will actually run at. 79 * 80 * %ebp contains the address we are loaded at by the boot loader and %ebx 81 * contains the address where we should move the kernel image temporarily 82 * for safe in-place decompression. 83 */ 84 85#ifdef CONFIG_RELOCATABLE 86 movl %ebp, %ebx 87 movl BP_kernel_alignment(%esi), %eax 88 decl %eax 89 addl %eax, %ebx 90 notl %eax 91 andl %eax, %ebx 92#else 93 movl $LOAD_PHYSICAL_ADDR, %ebx 94#endif 95 96 /* Target address to relocate to for decompression */ 97 addl $z_extract_offset, %ebx 98 99/* 100 * Prepare for entering 64 bit mode 101 */ 102 103 /* Load new GDT with the 64bit segments using 32bit descriptor */ 104 leal gdt(%ebp), %eax 105 movl %eax, gdt+2(%ebp) 106 lgdt gdt(%ebp) 107 108 /* Enable PAE mode */ 109 xorl %eax, %eax 110 orl $(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_64.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 */ 202 203 /* Setup data segments. */ 204 xorl %eax, %eax 205 movl %eax, %ds 206 movl %eax, %es 207 movl %eax, %ss 208 movl %eax, %fs 209 movl %eax, %gs 210 lldt %ax 211 movl $0x20, %eax 212 ltr %ax 213 214 /* 215 * Compute the decompressed kernel start address. It is where 216 * we were loaded at aligned to a 2M boundary. %rbp contains the 217 * decompressed kernel start address. 218 * 219 * If it is a relocatable kernel then decompress and run the kernel 220 * from load address aligned to 2MB addr, otherwise decompress and 221 * run the kernel from LOAD_PHYSICAL_ADDR 222 * 223 * We cannot rely on the calculation done in 32-bit mode, since we 224 * may have been invoked via the 64-bit entry point. 225 */ 226 227 /* Start with the delta to where the kernel will run at. */ 228#ifdef CONFIG_RELOCATABLE 229 leaq startup_32(%rip) /* - $startup_32 */, %rbp 230 movl BP_kernel_alignment(%rsi), %eax 231 decl %eax 232 addq %rax, %rbp 233 notq %rax 234 andq %rax, %rbp 235#else 236 movq $LOAD_PHYSICAL_ADDR, %rbp 237#endif 238 239 /* Target address to relocate to for decompression */ 240 leaq z_extract_offset(%rbp), %rbx 241 242 /* Set up the stack */ 243 leaq boot_stack_end(%rbx), %rsp 244 245 /* Zero EFLAGS */ 246 pushq $0 247 popfq 248 249/* 250 * Copy the compressed kernel to the end of our buffer 251 * where decompression in place becomes safe. 252 */ 253 pushq %rsi 254 leaq (_bss-8)(%rip), %rsi 255 leaq (_bss-8)(%rbx), %rdi 256 movq $_bss /* - $startup_32 */, %rcx 257 shrq $3, %rcx 258 std 259 rep movsq 260 cld 261 popq %rsi 262 263/* 264 * Jump to the relocated address. 265 */ 266 leaq relocated(%rbx), %rax 267 jmp *%rax 268 269 .text 270relocated: 271 272/* 273 * Clear BSS (stack is currently empty) 274 */ 275 xorl %eax, %eax 276 leaq _bss(%rip), %rdi 277 leaq _ebss(%rip), %rcx 278 subq %rdi, %rcx 279 shrq $3, %rcx 280 rep stosq 281 282/* 283 * Do the decompression, and jump to the new kernel.. 284 */ 285 pushq %rsi /* Save the real mode argument */ 286 movq %rsi, %rdi /* real mode address */ 287 leaq boot_heap(%rip), %rsi /* malloc area for uncompression */ 288 leaq input_data(%rip), %rdx /* input_data */ 289 movl $z_input_len, %ecx /* input_len */ 290 movq %rbp, %r8 /* output target address */ 291 call decompress_kernel 292 popq %rsi 293 294/* 295 * Jump to the decompressed kernel. 296 */ 297 jmp *%rbp 298 299 .data 300gdt: 301 .word gdt_end - gdt 302 .long gdt 303 .word 0 304 .quad 0x0000000000000000 /* NULL descriptor */ 305 .quad 0x00af9a000000ffff /* __KERNEL_CS */ 306 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 307 .quad 0x0080890000000000 /* TS descriptor */ 308 .quad 0x0000000000000000 /* TS continued */ 309gdt_end: 310 311/* 312 * Stack and heap for uncompression 313 */ 314 .bss 315 .balign 4 316boot_heap: 317 .fill BOOT_HEAP_SIZE, 1, 0 318boot_stack: 319 .fill BOOT_STACK_SIZE, 1, 0 320boot_stack_end: 321 322/* 323 * Space for page tables (not in .bss so not zeroed) 324 */ 325 .section ".pgtable","a",@nobits 326 .balign 4096 327pgtable: 328 .fill 6*4096, 1, 0 329