104 lines
2.1 KiB
NASM
104 lines
2.1 KiB
NASM
global flushTSS
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flushTSS:
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mov ax, 0x28
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ltr ax
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ret
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task_ptr: equ (0x310000-4)
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; return address in EAX
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; return stack in ECX
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; we can modify EAX, ECX, EDX
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; i.e. save all others in task
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global save_current_task
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save_current_task:
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push edx
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mov edx, esp ; EDX holds our tmp stack, unsaved
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mov esp, dword [task_ptr] ; load current task pointer
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push ss
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push ecx ; return stack
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pushfd
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push cs
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push eax ; return address
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push ds ; other segs, pop
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push es ; before iret
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push fs ; in exit handler
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push gs
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push ebp ; saved
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push ebx ; saved
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push esi ; saved
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push edi ; saved
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mov dword [task_ptr], esp ; save new task pointer
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mov esp, edx
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pop edx
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ret
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global return_prev_task
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return_prev_task:
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mov ecx, eax ; save return value for later
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mov edx, dword [task_ptr] ; load current task pointer
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add dword [task_ptr], 52 ; adjust to last task pointer
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mov edi, [edx+0]
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mov esi, [edx+4]
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mov ebx, [edx+8]
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mov ebp, [edx+12]
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mov eax, [edx+0+16] ; gs
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mov gs, ax
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mov eax, [edx+4+16] ; fs
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mov fs, ax
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mov eax, [edx+8+16] ; es
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mov es, ax
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; SS:ESP <- return stack
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mov esp, [edx+28+16] ; esp
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mov eax, [edx+32+16] ; ss
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mov ss, ax
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mov eax, [edx+24+16] ; eflags
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push eax
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mov eax, [edx+20+16] ; cs
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push eax
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mov eax, [edx+16+16] ; eip
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push eax
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mov eax, [edx+12+16] ; ds
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mov ds, ax
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mov eax, ecx ; restore return value
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iret
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; extern void enter_v86(uint32_t ss, uint32_t esp, uint32_t cs, uint32_t eip);
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global enter_v86
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enter_v86:
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pop eax ; return address
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mov ecx, esp ; return stack
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call save_current_task
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mov ebp, esp ; save stack pointer
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push dword [ebp+0] ; ss
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push dword [ebp+4] ; esp
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pushfd ; eflags
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or dword [esp], (1 << 17) ; set VM flags
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;or dword [esp], (3 << 12) ; IOPL 3
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push dword [ebp+8] ; cs
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push dword [ebp+12] ; eip
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iret
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; return address in eax, return stack in ebp
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;extern save_current_task
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extern user_test
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global jmp_usermode_test
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jmp_usermode_test:
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pop eax ; return address
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mov ecx, esp ; return stack
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call save_current_task
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mov esp, 0x800000 ; usermode stack
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mov eax, 0x20 | 3
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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 eax, esp
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push 0x20 | 3
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push eax
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pushfd
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push 0x18 | 3
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push user_test
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iret
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