diff options
Diffstat (limited to 'bootother.S')
| -rw-r--r-- | bootother.S | 75 |
1 files changed, 32 insertions, 43 deletions
diff --git a/bootother.S b/bootother.S index 899669a..186873e 100644 --- a/bootother.S +++ b/bootother.S @@ -9,80 +9,69 @@ # 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. +# Bootothers (in main.c) sends the STARTUPs one at a time. +# It copies this code (start) at 0x7000. +# It puts the address of a newly allocated per-core stack in start-4, +# and the address of the place to jump to (mpmain) 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 SEG_KCODE 1 +#define SEG_KDATA 2 -#define CR0_PE 1 // protected mode enable bit +#define CR0_PE 1 -.code16 # Assemble for 16-bit mode +.code16 .globl start start: - cli # Disable interrupts + cli - # 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 + movw %ax,%ds + movw %ax,%es + movw %ax,%ss //PAGEBREAK! - # Switch from real to protected mode, using a bootstrap GDT - # and segment translation that makes virtual addresses - # identical to 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 - # This ljmp is how you load the CS (Code Segment) register. - # SEG_ASM produces segment descriptors with the 32-bit mode - # flag set (the D flag), so addresses and word operands will - # default to 32 bits after this jump. ljmp $(SEG_KCODE<<3), $start32 -.code32 # Assemble for 32-bit mode +.code32 start32: - # 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 + movw $(SEG_KDATA<<3), %ax + movw %ax, %ds + movw %ax, %es + movw %ax, %ss + movw $0, %ax + movw %ax, %fs + movw %ax, %gs - # Set up the stack pointer and call into C. + # switch to the stack allocated by bootothers() movl start-4, %esp + + # call mpmain() call *(start-8) - # If the call returns (it shouldn't), trigger a Bochs - # breakpoint if running under Bochs, then loop. - movw $0x8a00, %ax # 0x8a00 -> port 0x8a00 + movw $0x8a00, %ax movw %ax, %dx outw %ax, %dx - movw $0x8ae0, %ax # 0x8ae0 -> port 0x8a00 + movw $0x8ae0, %ax outw %ax, %dx spin: jmp spin -# Bootstrap GDT -.p2align 2 # force 4 byte alignment +.p2align 2 gdt: - SEG_NULLASM # null seg - SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) # code seg - SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg + SEG_NULLASM + SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) + SEG_ASM(STA_W, 0x0, 0xffffffff) gdtdesc: - .word (gdtdesc - gdt - 1) # sizeof(gdt) - 1 - .long gdt # address gdt + .word (gdtdesc - gdt - 1) + .long gdt |