/* * linux/boot/head.S * * Copyright (C) 1991, 1992, 1993 Linus Torvalds */ /* * head.S contains the 32-bit startup code. * * NOTE!!! Startup happens at absolute address 0x00001000, which is also where * the page directory will exist. The startup code will be overwritten by * the page directory. [According to comments etc elsewhere on a compressed * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC] * * Page 0 is deliberately kept safe, since System Management Mode code in * laptops may need to access the BIOS data stored there. This is also * useful for future device drivers that either access the BIOS via VM86 * mode. */ /* * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996 */ .code32 .text #include #include #include #include #include .section ".text.head" .code32 .globl startup_32 startup_32: cld cli movl $(__KERNEL_DS), %eax movl %eax, %ds movl %eax, %es movl %eax, %ss /* Calculate the delta between where we were compiled to run * at and where we were actually loaded at. This can only be done * with a short local call on x86. Nothing else will tell us what * address we are running at. The reserved chunk of the real-mode * data at 0x34-0x3f are used as the stack for this calculation. * Only 4 bytes are needed. */ leal 0x40(%esi), %esp call 1f 1: popl %ebp subl $1b, %ebp /* setup a stack and make sure cpu supports long mode. */ movl $user_stack_end, %eax addl %ebp, %eax movl %eax, %esp call verify_cpu testl %eax, %eax jnz no_longmode /* Compute the delta between where we were compiled to run at * and where the code will actually run at. */ /* %ebp contains the address we are loaded at by the boot loader and %ebx * contains the address where we should move the kernel image temporarily * for safe in-place decompression. */ #ifdef CONFIG_RELOCATABLE movl %ebp, %ebx addl $(LARGE_PAGE_SIZE -1), %ebx andl $LARGE_PAGE_MASK, %ebx #else movl $CONFIG_PHYSICAL_START, %ebx #endif /* Replace the compressed data size with the uncompressed size */ subl input_len(%ebp), %ebx movl output_len(%ebp), %eax addl %eax, %ebx /* Add 8 bytes for every 32K input block */ shrl $12, %eax addl %eax, %ebx /* Add 32K + 18 bytes of extra slack and align on a 4K boundary */ addl $(32768 + 18 + 4095), %ebx andl $~4095, %ebx /* * Prepare for entering 64 bit mode */ /* Load new GDT with the 64bit segments using 32bit descriptor */ leal gdt(%ebp), %eax movl %eax, gdt+2(%ebp) lgdt gdt(%ebp) /* Enable PAE mode */ xorl %eax, %eax orl $(1 << 5), %eax movl %eax, %cr4 /* * Build early 4G boot pagetable */ /* Initialize Page tables to 0*/ leal pgtable(%ebx), %edi xorl %eax, %eax movl $((4096*6)/4), %ecx rep stosl /* Build Level 4 */ leal pgtable + 0(%ebx), %edi leal 0x1007 (%edi), %eax movl %eax, 0(%edi) /* Build Level 3 */ leal pgtable + 0x1000(%ebx), %edi leal 0x1007(%edi), %eax movl $4, %ecx 1: movl %eax, 0x00(%edi) addl $0x00001000, %eax addl $8, %edi decl %ecx jnz 1b /* Build Level 2 */ leal pgtable + 0x2000(%ebx), %edi movl $0x00000183, %eax movl $2048, %ecx 1: movl %eax, 0(%edi) addl $0x00200000, %eax addl $8, %edi decl %ecx jnz 1b /* Enable the boot page tables */ leal pgtable(%ebx), %eax movl %eax, %cr3 /* Enable Long mode in EFER (Extended Feature Enable Register) */ movl $MSR_EFER, %ecx rdmsr btsl $_EFER_LME, %eax wrmsr /* Setup for the jump to 64bit mode * * When the jump is performend we will be in long mode but * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use * the new gdt/idt that has __KERNEL_CS with CS.L = 1. * We place all of the values on our mini stack so lret can * used to perform that far jump. */ pushl $__KERNEL_CS leal startup_64(%ebp), %eax pushl %eax /* Enter paged protected Mode, activating Long Mode */ movl $0x80000001, %eax /* Enable Paging and Protected mode */ movl %eax, %cr0 /* Jump from 32bit compatibility mode into 64bit mode. */ lret no_longmode: /* This isn't an x86-64 CPU so hang */ 1: hlt jmp 1b #include "../../kernel/verify_cpu.S" /* Be careful here startup_64 needs to be at a predictable * address so I can export it in an ELF header. Bootloaders * should look at the ELF header to find this address, as * it may change in the future. */ .code64 .org 0x200 ENTRY(startup_64) /* We come here either from startup_32 or directly from a * 64bit bootloader. If we come here from a bootloader we depend on * an identity mapped page table being provied that maps our * entire text+data+bss and hopefully all of memory. */ /* Setup data segments. */ xorl %eax, %eax movl %eax, %ds movl %eax, %es movl %eax, %ss /* Compute the decompressed kernel start address. It is where * we were loaded at aligned to a 2M boundary. %rbp contains the * decompressed kernel start address. * * If it is a relocatable kernel then decompress and run the kernel * from load address aligned to 2MB addr, otherwise decompress and * run the kernel from CONFIG_PHYSICAL_START */ /* Start with the delta to where the kernel will run at. */ #ifdef CONFIG_RELOCATABLE leaq startup_32(%rip) /* - $startup_32 */, %rbp addq $(LARGE_PAGE_SIZE - 1), %rbp andq $LARGE_PAGE_MASK, %rbp movq %rbp, %rbx #else movq $CONFIG_PHYSICAL_START, %rbp movq %rbp, %rbx #endif /* Replace the compressed data size with the uncompressed size */ movl input_len(%rip), %eax subq %rax, %rbx movl output_len(%rip), %eax addq %rax, %rbx /* Add 8 bytes for every 32K input block */ shrq $12, %rax addq %rax, %rbx /* Add 32K + 18 bytes of extra slack and align on a 4K boundary */ addq $(32768 + 18 + 4095), %rbx andq $~4095, %rbx /* Copy the compressed kernel to the end of our buffer * where decompression in place becomes safe. */ leaq _end(%rip), %r8 leaq _end(%rbx), %r9 movq $_end /* - $startup_32 */, %rcx 1: subq $8, %r8 subq $8, %r9 movq 0(%r8), %rax movq %rax, 0(%r9) subq $8, %rcx jnz 1b /* * Jump to the relocated address. */ leaq relocated(%rbx), %rax jmp *%rax .section ".text" relocated: /* * Clear BSS */ xorq %rax, %rax leaq _edata(%rbx), %rdi leaq _end(%rbx), %rcx subq %rdi, %rcx cld rep stosb /* Setup the stack */ leaq user_stack_end(%rip), %rsp /* zero EFLAGS after setting rsp */ pushq $0 popfq /* * Do the decompression, and jump to the new kernel.. */ pushq %rsi # Save the real mode argument movq %rsi, %rdi # real mode address leaq _heap(%rip), %rsi # _heap leaq input_data(%rip), %rdx # input_data movl input_len(%rip), %eax movq %rax, %rcx # input_len movq %rbp, %r8 # output call decompress_kernel popq %rsi /* * Jump to the decompressed kernel. */ jmp *%rbp .data gdt: .word gdt_end - gdt .long gdt .word 0 .quad 0x0000000000000000 /* NULL descriptor */ .quad 0x00af9a000000ffff /* __KERNEL_CS */ .quad 0x00cf92000000ffff /* __KERNEL_DS */ gdt_end: .bss /* Stack for uncompression */ .balign 4 user_stack: .fill 4096,4,0 user_stack_end: