Subversion Repositories Kolibri OS

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;                                                              ;;

;; Copyright (C) KolibriOS team 2004-2011. All rights reserved. ;;

;; Distributed under terms of the GNU General Public License    ;;

;;                                                              ;;

;;                                                              ;;

;;  MenuetOS process management, protected ring3                ;;

;;                                                              ;;

;;  Distributed under GPL. See file COPYING for details.        ;;

;;  Copyright 2003 Ville Turjanmaa                              ;;

;;                                                              ;;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

$Revision: 3296 $

align 4 ;3A08

build_interrupt_table:

        mov     edi, idts

        mov     esi, sys_int

        mov     ecx, 0x40

        mov     eax, (10001110b shl 24) + os_code

  @@:

        movsw   ;low word of code-entry

        stosd   ;interrupt gate type : os_code selector

        movsw   ;high word of code-entry

        loop    @b

        movsd   ;copy low  dword of trap gate for int 0x40

        movsd   ;copy high dword of trap gate for int 0x40

        lidt    [esi]

        ret

iglobal

  align 4

  sys_int:

    ;exception handlers addresses (for interrupt gate construction)

        dd      e0,e1,e2,e3,e4,e5,e6,except_7 ; SEE: core/fpu.inc

        dd      e8,e9,e10,e11,e12,e13,page_fault_exc,e15

        dd      e16, e17,e18, e19

        times   12 dd unknown_interrupt ;int_20..int_31

    ;interrupt handlers addresses (for interrupt gate construction)

        ; 0x20 .. 0x2F - IRQ handlers

        dd      irq0, irq_serv.irq_1, irq_serv.irq_2

        dd      irq_serv.irq_3, irq_serv.irq_4

        dd      irq_serv.irq_5,  irq_serv.irq_6,  irq_serv.irq_7

        dd      irq_serv.irq_8,  irq_serv.irq_9,  irq_serv.irq_10

        dd      irq_serv.irq_11, irq_serv.irq_12, irqD, irq_serv.irq_14, irq_serv.irq_15

        dd irq_serv.irq_16

        dd irq_serv.irq_17

        dd irq_serv.irq_18

        dd irq_serv.irq_19

        dd irq_serv.irq_20

        dd irq_serv.irq_21

        dd irq_serv.irq_22

        dd irq_serv.irq_23

    times 32 - IRQ_RESERVED dd unknown_interrupt

    ;int_0x40 gate trap (for directly copied)

        dw      i40 and 0xFFFF, os_code, 11101111b shl 8, i40 shr 16

  idtreg: ; data for LIDT instruction (!!! must be immediately below sys_int data)

        dw      2*($-sys_int-4)-1

        dd      idts ;0x8000B100

        dw      0    ;ïðîñòî âûðàâíèâàíèå

  msg_fault_sel dd  msg_exc_8,msg_exc_u,msg_exc_a,msg_exc_b

                dd  msg_exc_c,msg_exc_d,msg_exc_e

  msg_exc_8     db "Double fault", 0

  msg_exc_u     db "Undefined Exception", 0

  msg_exc_a     db "Invalid TSS", 0

  msg_exc_b     db "Segment not present", 0

  msg_exc_c     db "Stack fault", 0

  msg_exc_d     db "General protection fault", 0

  msg_exc_e     db "Page fault", 0

  msg_sel_ker   db "kernel", 0

  msg_sel_app   db "application", 0

endg

macro save_ring3_context {

        pushad

}

macro restore_ring3_context {

        popad

}

macro exc_wo_code [num] {

  e#num :

        save_ring3_context

        mov     bl, num

        jmp     exc_c

} exc_wo_code   0,1,2,3,4,5,6,15,16,19

macro exc_w_code [num] {

  e#num :

        add     esp, 4

        save_ring3_context

        mov     bl, num

        jmp     exc_c

} exc_w_code    8,9,10,11,12,13,17,18

uglobal

  pf_err_code   dd ?

endg

page_fault_exc:                 ; äóðàêîóñòî÷èâîñòü: ñåëåêòîðû èñïîð÷åíû...

        pop     [ss:pf_err_code]; äåéñòâèòåëüíî äî ñëåäóþùåãî #PF

        save_ring3_context

        mov     bl, 14

exc_c:                          ; èñêëþ÷åíèÿ (âñå, êðîìå 7-ãî - #NM)

; Ôðýéì ñòåêà ïðè èñêëþ÷åíèè/ïðåðûâàíèè èç 3-ãî êîëüöà + pushad (ò.å., èìåííî çäåñü)

  reg_ss        equ esp+0x30

  reg_esp3      equ esp+0x2C

  reg_eflags    equ esp+0x28

  reg_cs3       equ esp+0x24

  reg_eip       equ esp+0x20

 ; ýòî ôðýéì îò pushad

  reg_eax       equ esp+0x1C

  reg_ecx       equ esp+0x18

  reg_edx       equ esp+0x14

  reg_ebx       equ esp+0x10

  reg_esp0      equ esp+0x0C

  reg_ebp       equ esp+0x08

  reg_esi       equ esp+0x04

  reg_edi       equ esp+0x00

        mov     ax, app_data        ;èñêëþ÷åíèå

        mov     ds, ax                  ;çàãðóçèì ïðàâèëüíûå çíà÷åíèÿ

        mov     es, ax                  ;â ðåãèñòðû

        cld                     ; è ïðèâîäèì DF ê ñòàíäàðòó

        movzx   ebx, bl

; redirect to V86 manager? (EFLAGS & 0x20000) != 0?

        test    byte[reg_eflags+2], 2

        jnz     v86_exc_c

        cmp     bl, 14          ; #PF

        jne     @f

        call    page_fault_handler ; SEE: core/memory.inc

  @@:

        mov     esi, [current_slot]

        btr     [esi+APPDATA.except_mask], ebx

        jnc     @f

        mov     eax, [esi+APPDATA.exc_handler]

        test    eax, eax

        jnz     IRetToUserHook

  @@:

        cli

        mov     eax, [esi+APPDATA.debugger_slot]

        test    eax, eax

        jnz     .debug

        sti

; not debuggee => say error and terminate

        call    show_error_parameters ;; only ONE using, inline ???

       ;mov     edx, [TASK_BASE]

        mov     [edx + TASKDATA.state], byte 4 ; terminate

        jmp     change_task     ; stack - here it does not matter at all, SEE: core/shed.inc

.debug:

; we are debugged process, notify debugger and suspend ourself

; eax=debugger PID

        mov     ecx, 1          ; debug_message code=other_exception

        cmp     bl, 1           ; #DB

        jne     .notify         ; notify debugger and suspend ourself

        mov     ebx, dr6        ; debug_message data=DR6_image

        xor     edx, edx

        mov     dr6, edx

        mov     edx, dr7

        mov     cl, not 8

  .l1:

        shl     dl, 2

        jc      @f

        and     bl, cl

  @@:

        sar     cl, 1

        jc      .l1

        mov     cl, 3           ; debug_message code=debug_exception

.notify:

        push    ebx             ; debug_message data

        mov     ebx, [TASK_BASE]

        push    [ebx+TASKDATA.pid] ; PID

        push    ecx             ; debug_message code ((here: ecx==1/3))

        mov     cl, 12          ; debug_message size

        call    debugger_notify ;; only ONE using, inline ??? SEE: core/debug.inc

        add     esp, 12

        mov     edx, [TASK_BASE]

        mov     byte [edx+TASKDATA.state], 1 ; suspended

        call    change_task     ; SEE: core/shed.inc

        restore_ring3_context

        iretd

IRetToUserHook:

        xchg    eax, [reg_eip]

        sub     dword[reg_esp3], 8

        mov     edi, [reg_esp3]

        stosd

        mov     [edi], ebx

        restore_ring3_context

; simply return control to interrupted process

unknown_interrupt:

        iretd

;-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

; bl - error vector

show_error_parameters:

        cmp     bl, 0x06

        jnz     .no_ud

        push    ebx

        mov     ebx, ud_user_message

        mov     ebp, notifyapp

        call    fs_execute_from_sysdir_param

        pop     ebx

.no_ud:

        mov     edx, [TASK_BASE];not scratched below

        DEBUGF  1, "K : Process - forced terminate PID: %x [%s]\n", [edx+TASKDATA.pid], [current_slot]

        cmp     bl, 0x08

        jb      .l0

        cmp     bl, 0x0e

        jbe     .l1

  .l0:

        mov     bl, 0x09

  .l1:

        mov     eax, [msg_fault_sel+ebx*4 - 0x08*4]

        DEBUGF  1, "K : %s\n", eax

        mov     eax, [reg_cs3+4]

        mov     edi, msg_sel_app

        mov     ebx, [reg_esp3+4]

        cmp     eax, app_code

        je      @f

        mov     edi, msg_sel_ker

        mov     ebx, [reg_esp0+4]

    @@:

        DEBUGF  1, "K : EAX : %x EBX : %x ECX : %x\n", [reg_eax+4], [reg_ebx+4], [reg_ecx+4]

        DEBUGF  1, "K : EDX : %x ESI : %x EDI : %x\n", [reg_edx+4], [reg_esi+4], [reg_edi+4]

        DEBUGF  1, "K : EBP : %x EIP : %x ESP : %x\n", [reg_ebp+4], [reg_eip+4], ebx

        DEBUGF  1, "K : Flags : %x CS : %x (%s)\n", [reg_eflags+4], eax, edi

        ret

;-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

  restore  reg_ss

  restore  reg_esp3

  restore  reg_eflags

  restore  reg_cs

  restore  reg_eip

  restore  reg_eax

  restore  reg_ecx

  restore  reg_edx

  restore  reg_ebx

  restore  reg_esp0

  restore  reg_ebp

  restore  reg_esi

  restore  reg_edi

align 4

set_application_table_status:

        push    eax

        mov     eax, [CURRENT_TASK]

        shl     eax, 5

        add     eax, CURRENT_TASK+TASKDATA.pid

        mov     eax, [eax]

        mov     [application_table_status], eax

        pop     eax

        ret

align 4

clear_application_table_status:

        push    eax

        mov     eax, [CURRENT_TASK]

        shl     eax, 5

        add     eax, CURRENT_TASK+TASKDATA.pid

        mov     eax, [eax]

        cmp     eax, [application_table_status]

        jne     apptsl1

        xor     eax, eax

        mov     [application_table_status], eax

      apptsl1:

        pop     eax

        ret

;  * eax = 64 - íîìåð ôóíêöèè

;  * ebx = 1 - åäèíñòâåííàÿ ïîäôóíêöèÿ

;  * ecx = íîâûé ðàçìåð ïàìÿòè

;Âîçâðàùàåìîå çíà÷åíèå:

;  * eax = 0 - óñïåøíî

;  * eax = 1 - íåäîñòàòî÷íî ïàìÿòè

align 4

sys_resize_app_memory:

        ; ebx = 1 - resize

        ; ecx = new amount of memory

;        cmp    eax,1

        dec     ebx

        jnz     .no_application_mem_resize

        stdcall new_mem_resize, ecx

        mov     [esp+32], eax

.no_application_mem_resize:

        ret

iglobal

;  process_terminating  db 'K : Process - terminating',13,10,0

;  process_terminated   db 'K : Process - done',13,10,0

  msg_obj_destroy       db 'K : destroy app object',13,10,0

endg

; param

;  esi= slot

align 4

terminate: ; terminate application

           .slot equ esp   ;locals

        push    esi        ;save .slot

        shl     esi, 8

        cmp     [SLOT_BASE+esi+APPDATA.dir_table], 0

        jne     @F

        pop     esi

        shl     esi, 5

        mov     [CURRENT_TASK+esi+TASKDATA.state], 9

        ret

@@:

           ;mov    esi,process_terminating

           ;call   sys_msg_board_str

@@:

        cli

        cmp     [application_table_status], 0

        je      term9

        sti

        call    change_task

        jmp     @b

term9:

        call    set_application_table_status

; if the process is in V86 mode...

        mov     eax, [.slot]

        shl     eax, 8

        mov     esi, [eax+SLOT_BASE+APPDATA.pl0_stack]

        add     esi, RING0_STACK_SIZE

        cmp     [eax+SLOT_BASE+APPDATA.saved_esp0], esi

        jz      .nov86

; ...it has page directory for V86 mode

        mov     esi, [eax+SLOT_BASE+APPDATA.saved_esp0]

        mov     ecx, [esi+4]

        mov     [eax+SLOT_BASE+APPDATA.dir_table], ecx

; ...and I/O permission map for V86 mode

        mov     ecx, [esi+12]

        mov     [eax+SLOT_BASE+APPDATA.io_map], ecx

        mov     ecx, [esi+8]

        mov     [eax+SLOT_BASE+APPDATA.io_map+4], ecx

.nov86:

        mov     esi, [.slot]

        shl     esi, 8

        add     esi, SLOT_BASE+APP_OBJ_OFFSET

@@:

        mov     eax, [esi+APPOBJ.fd]

        test    eax, eax

        jz      @F

        cmp     eax, esi

        je      @F

        push    esi

        call    [eax+APPOBJ.destroy]

           DEBUGF 1,"%s",msg_obj_destroy

        pop     esi

        jmp     @B

@@:

        mov     eax, [.slot]

        shl     eax, 8

        stdcall destroy_app_space, [SLOT_BASE+eax+APPDATA.dir_table], [SLOT_BASE+eax+APPDATA.dlls_list_ptr]

        mov     esi, [.slot]

        cmp     [fpu_owner], esi ; if user fpu last -> fpu user = 1

        jne     @F

        mov     [fpu_owner], 1

        mov     eax, [256+SLOT_BASE+APPDATA.fpu_state]

        clts

        bt      [cpu_caps], CAPS_SSE

        jnc     .no_SSE

        fxrstor [eax]

        jmp     @F

.no_SSE:

        fnclex

        frstor  [eax]

@@:

        mov     [KEY_COUNT], byte 0    ; empty keyboard buffer

        mov     [BTN_COUNT], byte 0    ; empty button buffer

; remove defined hotkeys

        mov     eax, hotkey_list

.loop:

        cmp     [eax+8], esi

        jnz     .cont

        mov     ecx, [eax]

        jecxz   @f

        push    dword [eax+12]

        pop     dword [ecx+12]

@@:

        mov     ecx, [eax+12]

        push    dword [eax]

        pop     dword [ecx]

        xor     ecx, ecx

        mov     [eax], ecx

        mov     [eax+4], ecx

        mov     [eax+8], ecx

        mov     [eax+12], ecx

.cont:

        add     eax, 16

        cmp     eax, hotkey_list+256*16

        jb      .loop

; get process PID

        mov     eax, esi

        shl     eax, 5

        mov     eax, [eax+CURRENT_TASK+TASKDATA.pid]

; compare current lock input with process PID

        cmp     eax, [PID_lock_input]

        jne     @f

        xor     eax, eax

        mov     [PID_lock_input], eax

@@:

; remove hotkeys in buffer

        mov     eax, hotkey_buffer

.loop2:

        cmp     [eax], esi

        jnz     .cont2

        and     dword [eax+4], 0

        and     dword [eax], 0

.cont2:

        add     eax, 8

        cmp     eax, hotkey_buffer+120*8

        jb      .loop2

        mov     ecx, esi          ; remove buttons

  bnewba2:

        mov     edi, [BTN_ADDR]

        mov     eax, edi

        cld

        movzx   ebx, word [edi]

        inc     bx

  bnewba:

        dec     bx

        jz      bnmba

        add     eax, 0x10

        cmp     cx, [eax]

        jnz     bnewba

        pusha

        mov     ecx, ebx

        inc     ecx

        shl     ecx, 4

        mov     ebx, eax

        add     eax, 0x10

        call    memmove

        dec     dword [edi]

        popa

        jmp     bnewba2

  bnmba:

        pusha   ; save window coordinates for window restoring

        cld

        shl     esi, 5

        add     esi, window_data

        mov     eax, [esi+WDATA.box.left]

        mov     [draw_limits.left], eax

        add     eax, [esi+WDATA.box.width]

        mov     [draw_limits.right], eax

        mov     eax, [esi+WDATA.box.top]

        mov     [draw_limits.top], eax

        add     eax, [esi+WDATA.box.height]

        mov     [draw_limits.bottom], eax

        xor     eax, eax

        mov     [esi+WDATA.box.left], eax

        mov     [esi+WDATA.box.width], eax

        mov     [esi+WDATA.box.top], eax

        mov     [esi+WDATA.box.height], eax

        mov     [esi+WDATA.cl_workarea], eax

        mov     [esi+WDATA.cl_titlebar], eax

        mov     [esi+WDATA.cl_frames], eax

        mov     dword [esi+WDATA.reserved], eax; clear all flags: wstate, redraw, wdrawn

        lea     edi, [esi-window_data+draw_data]

        mov     ecx, 32/4

        rep stosd

        popa

; debuggee test

        pushad

        mov     edi, esi

        shl     edi, 5

        mov     eax, [SLOT_BASE+edi*8+APPDATA.debugger_slot]

        test    eax, eax

        jz      .nodebug

        push    8

        pop     ecx

        push    dword [CURRENT_TASK+edi+TASKDATA.pid]; PID

        push    2

        call    debugger_notify

        pop     ecx

        pop     ecx

.nodebug:

        popad

        mov     ebx, [.slot]

        shl     ebx, 8

        push    ebx

        mov     ebx, [SLOT_BASE+ebx+APPDATA.pl0_stack]

        stdcall kernel_free, ebx

        pop     ebx

        mov     ebx, [SLOT_BASE+ebx+APPDATA.cur_dir]

        stdcall kernel_free, ebx

        mov     edi, [.slot]

        shl     edi, 8

        add     edi, SLOT_BASE

        mov     eax, [edi+APPDATA.io_map]

        cmp     eax, [SLOT_BASE+256+APPDATA.io_map]

        je      @F

        call    free_page

@@:

        mov     eax, [edi+APPDATA.io_map+4]

        cmp     eax, [SLOT_BASE+256+APPDATA.io_map+4]

        je      @F

        call    free_page

@@:

        mov     eax, 0x20202020

        stosd

        stosd

        stosd

        mov     ecx, 244/4

        xor     eax, eax

        rep stosd

  ; activate window

        movzx   eax, word [WIN_STACK + esi*2]

        cmp     eax, [TASK_COUNT]

        jne     .dont_activate

        pushad

 .check_next_window:

        dec     eax

        cmp     eax, 1

        jbe     .nothing_to_activate

        lea     esi, [WIN_POS+eax*2]

        movzx   edi, word [esi]              ; edi = process

        shl     edi, 5

        cmp     [CURRENT_TASK + edi + TASKDATA.state], byte 9 ; skip dead slots

        je      .check_next_window

        add     edi, window_data

; \begin{diamond}[19.09.2006]

; skip minimized windows

        test    [edi + WDATA.fl_wstate], WSTATE_MINIMIZED

        jnz     .check_next_window

; \end{diamond}

        call    waredraw

 .nothing_to_activate:

        popad

 .dont_activate:

        push    esi     ; remove hd1 & cd & flp reservation

        shl     esi, 5

        mov     esi, [esi+CURRENT_TASK+TASKDATA.pid]

        cmp     [hd1_status], esi

        jnz     @f

        call    free_hd_channel

        and     [hd1_status], 0

@@:

        cmp     [cd_status], esi

        jnz     @f

        call    free_cd_channel

        and     [cd_status], 0

@@:

        cmp     [flp_status], esi

        jnz     @f

        and     [flp_status], 0

@@:

        pop     esi

        cmp     [bgrlockpid], esi

        jnz     @f

        and     [bgrlockpid], 0

        and     [bgrlock], 0

@@:

        pusha                 ; remove all port reservations

        mov     edx, esi

        shl     edx, 5

        add     edx, CURRENT_TASK

        mov     edx, [edx+TASKDATA.pid]

  rmpr0:

        mov     esi, [RESERVED_PORTS]

        test    esi, esi

        jz      rmpr9

  rmpr3:

        mov     edi, esi

        shl     edi, 4

        add     edi, RESERVED_PORTS

        cmp     edx, [edi]

        je      rmpr4

        dec     esi

        jnz     rmpr3

        jmp     rmpr9

  rmpr4:

        mov     ecx, 256

        sub     ecx, esi

        shl     ecx, 4

        mov     esi, edi

        add     esi, 16

        cld

        rep movsb

        dec     dword [RESERVED_PORTS]

        jmp     rmpr0

  rmpr9:

        popa

        mov     edi, esi ; do not run this process slot

        shl     edi, 5

        mov     [edi+CURRENT_TASK + TASKDATA.state], byte 9

; debugger test - terminate all debuggees

        mov     eax, 2

        mov     ecx, SLOT_BASE+2*0x100+APPDATA.debugger_slot

.xd0:

        cmp     eax, [TASK_COUNT]

        ja      .xd1

        cmp     dword [ecx], esi

        jnz     @f

        and     dword [ecx], 0

        pushad

        xchg    eax, ecx

        mov     ebx, 2

        call    sys_system

        popad

@@:

        inc     eax

        add     ecx, 0x100

        jmp     .xd0

.xd1:

;    call  systest

        sti     ; .. and life goes on

        mov     eax, [draw_limits.left]

        mov     ebx, [draw_limits.top]

        mov     ecx, [draw_limits.right]

        mov     edx, [draw_limits.bottom]

        call    calculatescreen

        xor     eax, eax

        xor     esi, esi

        call    redrawscreen

        mov     [MOUSE_BACKGROUND], byte 0; no mouse background

        mov     [DONT_DRAW_MOUSE], byte 0; draw mouse

        and     [application_table_status], 0

    ;mov   esi,process_terminated

    ;call  sys_msg_board_str

        add     esp, 4

        ret

restore .slot

;iglobal

;if lang eq ru

;  boot_sched_1    db   '‘®§¤ ­¨¥ GDT TSS 㪠§ â¥«ï',0

;  boot_sched_2    db   '‘®§¤ ­¨¥ IDT â ¡«¨æë',0

;else

;  boot_sched_1    db   'Building gdt tss pointer',0

;  boot_sched_2    db   'Building IDT table',0

;end if

;endg

;build_scheduler:

;        mov     esi, boot_sched_1

;        call    boot_log

;        call   build_process_gdt_tss_pointer

;        mov    esi,boot_sched_2

;        call   boot_log

;        ret

; Three following procedures are used to guarantee that

; some part of kernel code will not be terminated from outside

; while it is running.

; Note: they do not protect a thread from terminating due to errors inside

; the thread; accessing a nonexisting memory would still terminate it.

; First two procedures must be used in pair by thread-to-be-protected

; to signal the beginning and the end of an important part.

; It is OK to have nested areas.

; The last procedure must be used by outside wanna-be-terminators;

; if it is safe to terminate the given thread immediately, it returns eax=1;

; otherwise, it returns eax=0 and notifies the target thread that it should

; terminate itself when leaving a critical area (the last critical area if

; they are nested).

; Implementation. Those procedures use one dword in APPDATA for the thread,

; APPDATA.terminate_protection.

; * The upper bit is 1 during normal operations and 0 when terminate is requested.

; * Other bits form a number = depth of critical regions,

;   plus 1 if the upper bit is 1.

; * When this dword goes to zero, the thread should be destructed,

;   and the procedure in which it happened becomes responsible for destruction.

; Enter critical area. Called by thread which wants to be protected.

proc protect_from_terminate

        mov     edx, [current_slot]

; Atomically increment depth of critical areas and get the old value.

        mov     eax, 1

        lock xadd [edx+APPDATA.terminate_protection], eax

; If the old value was zero, somebody has started to terminate us,

; so we are destructing and cannot do anything protected.

; Otherwise, return to the caller.

        test    eax, eax

        jz      @f

        ret

@@:

; Wait for somebody to finish us.

        call    change_task

        jmp     @b

endp

; Leave critical area. Called by thread which wants to be protected.

proc unprotect_from_terminate

        mov     edx, [current_slot]

; Atomically decrement depth of critical areas.

        lock dec [edx+APPDATA.terminate_protection]

; If the result of decrement is zero, somebody has requested termination,

; but at that moment we were inside a critical area; terminate now.

        jz      sys_end

; Otherwise, return to the caller.

        ret

endp

; Request termination of thread identified by edx = SLOT_BASE + slot*256.

; Called by anyone.

proc request_terminate

        xor     eax, eax        ; set return value

; Atomically clear the upper bit. If it was already zero, then

; somebody has requested termination before us, so just exit.

        lock btr [edx+APPDATA.terminate_protection], 31

        jnc     .unsafe

; Atomically decrement depth of critical areas.

        lock dec [edx+APPDATA.terminate_protection]

; If the result of decrement is nonzero, the target thread is inside a

; critical area; leave termination to leaving that area.

        jnz     .unsafe

; Otherwise, it is safe to kill the target now and the caller is responsible

; for this. Return eax=1.

        inc     eax

.unsafe:

        ret

endp