87 lines
3 KiB
ArmAsm
87 lines
3 KiB
ArmAsm
#include "asm.h"
|
|
|
|
# Each non-boot CPU ("AP") is started up in response to a STARTUP
|
|
# IPI from the boot CPU. Section B.4.2 of the Multi-Processor
|
|
# Specification says that the AP will start in real mode with CS:IP
|
|
# set to XY00:0000, where XY is an 8-bit value sent with the
|
|
# STARTUP. Thus this code must start at a 4096-byte boundary.
|
|
#
|
|
# Because this code sets DS to zero, it must sit
|
|
# at an address in the low 2^16 bytes.
|
|
#
|
|
# Bootothers (in main.c) sends the STARTUPs, one at a time.
|
|
# It puts this code (start) at 0x7000.
|
|
# It puts the correct %esp in start-4,
|
|
# and the place to jump to in start-8.
|
|
#
|
|
# This code is identical to bootasm.S except:
|
|
# - it does not need to enable A20
|
|
# - it uses the address at start-4 for the %esp
|
|
# - it jumps to the address at start-8 instead of calling bootmain
|
|
|
|
#define SEG_KCODE 1 // kernel code
|
|
#define SEG_KDATA 2 // kernel data+stack
|
|
|
|
#define CR0_PE 1 // protected mode enable bit
|
|
|
|
.code16 # Assemble for 16-bit mode
|
|
.globl start
|
|
start:
|
|
cli # Disable interrupts
|
|
|
|
# Set up the important data segment registers (DS, ES, SS).
|
|
xorw %ax,%ax # Segment number zero
|
|
movw %ax,%ds # -> Data Segment
|
|
movw %ax,%es # -> Extra Segment
|
|
movw %ax,%ss # -> Stack Segment
|
|
|
|
//PAGEBREAK!
|
|
# Switch from real to protected mode, using a bootstrap GDT
|
|
# and segment translation that makes virtual addresses
|
|
# identical to their physical addresses, so that the
|
|
# effective memory map does not change during the switch.
|
|
lgdt gdtdesc
|
|
movl %cr0, %eax
|
|
orl $CR0_PE, %eax
|
|
movl %eax, %cr0
|
|
|
|
# Jump to next instruction, but in 32-bit code segment.
|
|
# Switches processor into 32-bit mode.
|
|
ljmp $(SEG_KCODE<<3), $protcseg
|
|
|
|
.code32 # Assemble for 32-bit mode
|
|
protcseg:
|
|
# Set up the protected-mode data segment registers
|
|
movw $(SEG_KDATA<<3), %ax # Our data segment selector
|
|
movw %ax, %ds # -> DS: Data Segment
|
|
movw %ax, %es # -> ES: Extra Segment
|
|
movw %ax, %ss # -> SS: Stack Segment
|
|
movw $0, %ax # Zero segments not ready for use
|
|
movw %ax, %fs # -> FS
|
|
movw %ax, %gs # -> GS
|
|
|
|
movl start-4, %esp
|
|
movl start-8, %eax
|
|
call *%eax
|
|
|
|
# If bootmain returns (it shouldn't), trigger a Bochs
|
|
# breakpoint if running under Bochs, then loop.
|
|
movw $0x8a00, %ax # 0x8a00 -> port 0x8a00
|
|
movw %ax, %dx
|
|
outw %ax, %dx
|
|
movw $0x8e00, %ax # 0x8e00 -> port 0x8a00
|
|
outw %ax, %dx
|
|
spin:
|
|
jmp spin
|
|
|
|
# Bootstrap GDT
|
|
.p2align 2 # force 4 byte alignment
|
|
gdt:
|
|
SEG_NULLASM # null seg
|
|
SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) # code seg
|
|
SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg
|
|
|
|
gdtdesc:
|
|
.word (gdtdesc - gdt - 1) # sizeof(gdt) - 1
|
|
.long gdt # address gdt
|