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bootasm cleanup

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This commit is contained in:
Russ Cox 2009-07-11 19:15:32 -07:00
parent 8b75366ce4
commit 887f19686c
2 changed files with 12 additions and 12 deletions
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3
bootasm.S
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@ -86,8 +86,7 @@ gdt:
SEG_NULLASM # null seg SEG_NULLASM # null seg
SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) # code seg SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) # code seg
SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg
SEG_ASM(STA_W, 0x100, 0xffffffff) # per-cpu data seg; 0x100 is okay for now
gdtdesc: gdtdesc:
.word 0x1f # sizeof(gdt) - 1 .word (gdtdesc - gdt - 1) # sizeof(gdt) - 1
.long gdt # address gdt .long gdt # address gdt

21
bootother.S
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@ -19,15 +19,15 @@
# - it uses the address at start-4 for the %esp # - it uses the address at start-4 for the %esp
# - it jumps to the address at start-8 instead of calling bootmain # - it jumps to the address at start-8 instead of calling bootmain
.set PROT_MODE_CSEG, 0x8 # kernel code segment selector #define SEG_KCODE 1 // kernel code
.set PROT_MODE_DSEG, 0x10 # kernel data segment selector #define SEG_KDATA 2 // kernel data+stack
.set CR0_PE_ON, 0x1 # protected mode enable flag
#define CR0_PE 1 // protected mode enable bit
.code16 # Assemble for 16-bit mode
.globl start .globl start
start: start:
.code16 # Assemble for 16-bit mode
cli # Disable interrupts cli # Disable interrupts
cld # String operations increment
# Set up the important data segment registers (DS, ES, SS). # Set up the important data segment registers (DS, ES, SS).
xorw %ax,%ax # Segment number zero xorw %ax,%ax # Segment number zero
@ -42,22 +42,23 @@ start:
# effective memory map does not change during the switch. # effective memory map does not change during the switch.
lgdt gdtdesc lgdt gdtdesc
movl %cr0, %eax movl %cr0, %eax
orl $CR0_PE_ON, %eax orl $CR0_PE, %eax
movl %eax, %cr0 movl %eax, %cr0
# Jump to next instruction, but in 32-bit code segment. # Jump to next instruction, but in 32-bit code segment.
# Switches processor into 32-bit mode. # Switches processor into 32-bit mode.
ljmp $PROT_MODE_CSEG, $protcseg ljmp $(SEG_KCODE<<3), $protcseg
.code32 # Assemble for 32-bit mode .code32 # Assemble for 32-bit mode
protcseg: protcseg:
# Set up the protected-mode data segment registers # Set up the protected-mode data segment registers
movw $PROT_MODE_DSEG, %ax # Our data segment selector movw $(SEG_KDATA<<3), %ax # Our data segment selector
movw %ax, %ds # -> DS: Data Segment movw %ax, %ds # -> DS: Data Segment
movw %ax, %es # -> ES: Extra 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, %fs # -> FS
movw %ax, %gs # -> GS movw %ax, %gs # -> GS
movw %ax, %ss # -> SS: Stack Segment
movl start-4, %esp movl start-4, %esp
movl start-8, %eax movl start-8, %eax
@ -81,5 +82,5 @@ gdt:
SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg
gdtdesc: gdtdesc:
.word 0x17 # sizeof(gdt) - 1 .word (gdtdesc - gdt - 1) # sizeof(gdt) - 1
.long gdt # address gdt .long gdt # address gdt