diff options
Diffstat (limited to 'kernel/startup.S')
| -rw-r--r-- | kernel/startup.S | 153 |
1 files changed, 153 insertions, 0 deletions
diff --git a/kernel/startup.S b/kernel/startup.S new file mode 100644 index 0000000..1cae13c --- /dev/null +++ b/kernel/startup.S @@ -0,0 +1,153 @@ +/* +** @file startup.S +** +** @author Jon Coles +** @authors Warren R. Carithers, K. Reek +** +** SP startup code. +** +** This code prepares the various registers for execution of +** the program. It sets up all the segment registers and the +** runtime stack. By the time this code is running, we're in +** protected mode already. +*/ + +#define KERNEL_SRC +#define ASM_SRC + + .arch i386 + +#include <common.h> +#include <bootstrap.h> +#include <x86/arch.h> +#include <x86/bios.h> +#include <vm.h> + +/* +** Configuration options - define in Makefile +** +** CLEAR_BSS include code to clear all BSS space +** OS_CONFIG OS-related (vs. just standalone) variations +*/ + +/* +** A symbol for locating the beginning of the code. +*/ + .globl begtext + + .text +begtext: + +/* +** The entry point. When we get here, we have just entered protected +** mode, so all the segment registers are incorrect except for CS. +*/ + .globl _start + +_start: + cli /* seems to be reset on entry to p. mode */ + movb $NMI_ENABLE, %al /* re-enable NMIs (bootstrap */ + outb $CMOS_ADDR /* turned them off) */ + +/* +** Set the data and stack segment registers (code segment register +** was set by the long jump that switched us into protected mode). +*/ + xorl %eax, %eax /* clear EAX */ + movw $GDT_DATA, %ax /* GDT entry #3 - data segment */ + movw %ax, %ds /* for all four data segment registers */ + movw %ax, %es + movw %ax, %fs + movw %ax, %gs + + movw $GDT_STACK, %ax /* entry #4 is the stack segment */ + movw %ax, %ss + + movl $TARGET_STACK, %esp /* set up the system stack pointer */ + +#ifdef CLEAR_BSS +/* +** Zero the BSS segment +** +** These symbols are defined automatically by the linker, but they're +** defined at their virtual addresses rather than their physical addresses, +** and we haven't enabled paging yet. +*/ + .globl __bss_start, _end + + movl $V2P(__bss_start), %edi +clearbss: + movl $0, (%edi) + addl $4, %edi + cmpl $V2P(_end), %edi + jb clearbss +#endif /* CLEAR_BSS */ + +/* +** Enable paging. We use "large" pages for the initial page directory +** so that a one-level hierarchy will work for us. Once we have set +** up our memory freelist, we'll create a two-level hierarchy using +** "normal" 4KB pages. +*/ + # enable large pages + movl %cr4, %eax + orl $(CR4_PSE), %eax + movl %eax, %cr4 + + # set the page directory + .globl firstpdir + movl $(V2P(firstpdir)+0x1000), %eax + movl %eax, %cr3 + + # turn on paging + movl %cr0, %eax + orl $(CR0_PG), %eax + movl %eax, %cr0 + + # reset our stack pointer + movl $(kstack + SZ_KSTACK), %esp + + # set the initial frame pointer + xorl %ebp, %ebp + +/* +** Call the system initialization routine, and switch to +** executing at high addresses. We use an indirect jump +** here to avoid getting a PC-relative 'jmp' instruction. +** +** Alternate idea: push the address of isr_restore +** and just do an indirect jump? +*/ + .globl main + + movl $main, %eax + call *%eax + +/* +** At this point, main() must have created the first user +** process, and we're ready to shift into user mode. The user +** stack for that process must have the initial context in it; +** we treat this as a "return from interrupt" event, and just +** transfer to the code that restores the user context. +*/ + + .globl isr_restore + jmp isr_restore + + .data + +/* +** Define the kernel stack here, at a multiple-of-16 address +*/ + .p2align 4 + .globl kstack +kstack: .space SZ_KSTACK, 0 + +/* +** Define the initial kernel ESP here, as well. It should point +** to the first byte after the stack. +*/ + + .globl kernel_esp +kernel_esp: + .long kstack + SZ_KSTACK |