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Rev Author Line No. Line
1 ha 1 
iglobal
2 
  prev_user_of_fpu dd 0x1 ; set to OS
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endg
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label fpu_tss at 0xB080
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label fpu_stack dword at 0xB060
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align 4
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fpu_handler:
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        ; clear TS flag in CR0 -> for task switching
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        clts
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        ; save FPU context of the previous task
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        mov    eax,[prev_user_of_fpu]
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        shl    eax,8
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        add    eax,0x80000+0x10
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        fsave  [eax]
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        ; next task switch save our FPU context
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        ; now restore context of current task (if exists)
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        mov    eax,[0x3000]
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        mov    [prev_user_of_fpu],eax
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        shl    eax,8
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        add    eax,0x80000
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        cmp    [eax+0x7f],byte 0
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        je     bs7_first_fpu
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        frstor [eax+0x10]
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      bs7_first_fpu:
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        mov    [eax+0x7f],byte 1
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        ; prepare structure in stack for proper IRET
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        movzx  eax,word [fpu_tss+l.ss-tss_sceleton]  ; push ss
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        push   eax
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        mov    eax,[fpu_tss+l.esp-tss_sceleton]      ; push esp
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        push   eax
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        mov    eax,[fpu_tss+l.eflags-tss_sceleton]   ; push eflags
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        push   eax
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        movzx  eax,word [fpu_tss+l.cs-tss_sceleton]  ; push cs
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        push   eax
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        mov    eax,[fpu_tss+l.eip-tss_sceleton]      ; push eip
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        push   eax
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        ; save eax
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        push   dword [fpu_tss+l.eax-tss_sceleton]
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        ; restore all segment registers
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        mov    ax,[fpu_tss+l.es-tss_sceleton]
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        mov    es,ax
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        mov    ax,[fpu_tss+l.fs-tss_sceleton]
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        mov    fs,ax
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        mov    ax,[fpu_tss+l.gs-tss_sceleton]
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        mov    gs,ax
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        mov    ax,[fpu_tss+l.ds-tss_sceleton]
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        mov    ds,ax
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        ; restore eax
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        pop    eax
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        iret