forked from BSB-WS23/mpstubs
67 lines
1.8 KiB
NASM
67 lines
1.8 KiB
NASM
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; Startup of the remaining application processors (in real mode)
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; and switching to 'Protected Mode' with a temporary GDT.
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; This code is relocated by ApplicationProcessor::relocateSetupCode()
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[SECTION .setup_ap_seg]
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[GLOBAL setup_ap_gdt]
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[GLOBAL setup_ap_gdtd]
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; Unlike the bootstrap processor, the application processors have not been
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; setup by the boot loader -- they start in real mode (16 bit) and have to be
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; switched manually to protected mode (32 bit)
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[BITS 16]
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setup_ap:
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; Initialize segment register
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mov ax, cs ; Code segment and...
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mov ds, ax ; .. data segment should point to the same segment
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; (we don't use stack / stack segment)
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; Disable interrupts
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cli
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; Disable non maskable interrupts (NMI)
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mov al, 0x80
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out 0x70, al
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; load temporary real mode Global Descriptor Table (GDT)
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lgdt [setup_ap_gdtd - setup_ap]
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; Switch to protected mode:
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; enable protected mode bit (1 << 0) in control register 0
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mov eax, cr0
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or eax, 1
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mov cr0, eax
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; Far jump to 32 bit `startup_ap` function
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jmp dword 0x08:startup_ap
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; memory reserved for temporary real mode GDT
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; initialized by ApplicationProcessor::relocateSetupCode()
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ALIGN 4
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setup_ap_gdt:
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dq 0,0,0,0,0 ; reserve memory for at least 5 GDT entries
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; memory reserved for temporary real mode GDT descriptor
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; initialized by ApplicationProcessor::relocateSetupCode()
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setup_ap_gdtd:
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dw 0,0,0,0,0 ; reserve memory for GDT descriptor
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[SECTION .text]
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[BITS 32]
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; Segment initialization defined in `boot/startup.asm`
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[EXTERN segment_init]
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; protected mode (32 bit) startup code for application processor
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startup_ap:
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; reload all segment selectors (since they still point to the real mode GDT)
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mov ax, 0x10
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mov ds, ax
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mov es, ax
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mov fs, ax
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mov gs, ax
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mov ss, ax
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; Use same segment initialization function as bootstrap processor
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jmp segment_init
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