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bring bootasm and bootother more in sync

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rsc 2007-08-24 19:25:52 +00:00
parent 5d1f4b8a3a
commit 2bc72bdd29
2 changed files with 48 additions and 58 deletions
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56
bootasm.S
View file

@ -9,16 +9,17 @@
.set PROT_MODE_DSEG, 0x10 # kernel data segment selector
.set CR0_PE_ON, 0x1 # protected mode enable flag
.globl start # Entry point
.globl start
start:
.code16 # This runs in real mode
cli # Disable interrupts
.code16 # Assemble for 16-bit mode
cli # Disable interrupts
cld # String operations increment
# 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
xorw %ax,%ax # Segment number zero
movw %ax,%ds # -> Data Segment
movw %ax,%es # -> Extra Segment
movw %ax,%ss # -> Stack Segment
# Enable A20:
# For backwards compatibility with the earliest PCs, physical
@ -40,28 +41,21 @@ seta20.2:
movb $0xdf,%al # 0xdf -> port 0x60
outb %al,$0x60
# Switch from real to protected mode
# The descriptors in our GDT allow all physical memory to be accessed.
# Furthermore, the descriptors have base addresses of 0, so that the
# segment translation is a NOP, ie. virtual addresses are identical to
# their physical addresses. With this setup, immediately after
# enabling protected mode it will still appear to this code
# that it is running directly on physical memory with no translation.
# This initial NOP-translation setup is required by the processor
# to ensure that the transition to protected mode occurs smoothly.
real_to_prot:
cli # Mandatory since we dont set up an IDT
lgdt gdtdesc # load GDT -- mandatory in protected mode
movl %cr0, %eax # turn on protected mode
orl $CR0_PE_ON, %eax #
movl %eax, %cr0 #
### CPU magic: jump to relocation, flush prefetch queue, and reload %cs
### Has the effect of just jmp to the next instruction, but simultaneous
### loads CS with $PROT_MODE_CSEG.
//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_ON, %eax
movl %eax, %cr0
# Jump to next instruction, but in 32-bit code segment.
# Switches processor into 32-bit mode.
ljmp $PROT_MODE_CSEG, $protcseg
#### we are in 32-bit protected mode (hence the .code32)
.code32
.code32 # Assemble for 32-bit mode
protcseg:
# Set up the protected-mode data segment registers
movw $PROT_MODE_DSEG, %ax # Our data segment selector
@ -71,13 +65,13 @@ protcseg:
movw %ax, %gs # -> GS
movw %ax, %ss # -> SS: Stack Segment
# Set up the stack pointer, growing downward from 0x7c00.
# Set up the stack pointer and call into C.
movl $start, %esp
call cmain
call cmain # finish the boot load from C.
# cmain() should not return
# If cmain returns (it shouldn't), loop.
spin:
jmp spin # ..but in case it does, spin
jmp spin
# Bootstrap GDT
.p2align 2 # force 4 byte alignment

50
bootother.S
View file

@ -12,14 +12,19 @@
# mp.c causes each non-boot CPU in turn to jump to start.
# mp.c 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 0(start-4) for the %esp
# - it jumps to 0(start-8) instead of calling cmain
.set PROT_MODE_CSEG,0x8 # code segment selector
.set PROT_MODE_DSEG,0x10 # data segment selector
.set CR0_PE_ON,0x1 # protected mode enable flag
.set PROT_MODE_CSEG, 0x8 # kernel code segment selector
.set PROT_MODE_DSEG, 0x10 # kernel data segment selector
.set CR0_PE_ON, 0x1 # protected mode enable flag
.globl start
start:
.code16 # This runs in real mode
.code16 # Assemble for 16-bit mode
cli # Disable interrupts
cld # String operations increment
@ -29,31 +34,21 @@ start:
movw %ax,%es # -> Extra Segment
movw %ax,%ss # -> Stack Segment
# Set up the stack pointer, growing downward from 0x7000-8.
movw $start-8,%sp # Stack Pointer
//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_ON, %eax
movl %eax, %cr0
# Switch from real to protected mode
# The descriptors in our GDT allow all physical memory to be accessed.
# Furthermore, the descriptors have base addresses of 0, so that the
# segment translation is a NOP, ie. virtual addresses are identical to
# their physical addresses. With this setup, immediately after
# enabling protected mode it will still appear to this code
# that it is running directly on physical memory with no translation.
# This initial NOP-translation setup is required by the processor
# to ensure that the transition to protected mode occurs smoothly.
lgdt gdtdesc # load GDT -- mandatory in protected mode
movl %cr0, %eax # turn on protected mode
orl $CR0_PE_ON, %eax #
movl %eax, %cr0 #
# CPU magic: jump to relocation, flush prefetch queue, and reload %cs
# Has the effect of just jmp to the next instruction, but simultaneous
# loads CS with $PROT_MODE_CSEG.
# Jump to next instruction, but in 32-bit code segment.
# Switches processor into 32-bit mode.
ljmp $PROT_MODE_CSEG, $protcseg
# We are now in 32-bit protected mode (hence the .code32)
.code32
.code32 # Assemble for 32-bit mode
protcseg:
# Set up the protected-mode data segment registers
movw $PROT_MODE_DSEG, %ax # Our data segment selector
@ -63,10 +58,11 @@ protcseg:
movw %ax, %gs # -> GS
movw %ax, %ss # -> SS: Stack Segment
movl start-8, %eax
movl start-4, %esp
movl start-8, %eax
jmp *%eax
# Bootstrap GDT
.p2align 2 # force 4 byte alignment
gdt:
SEG_NULLASM # null seg