Resource for Source: C/C++

home *** CD-ROM | disk | FTP | other *** search

/ Resource for Source: C/C++ / Resource for Source - C-C++.iso / codelib2 / v_02_10 / 2n10062a < prev next >

Wrap

Text File | 1995-11-01 | 16.7 KB | 617 lines

COMMENT ~ --------------------------------------------------------- LISTING 1 File: breakout.asm This module contains routines necessary to enable Ctrl-Break to "break out" of infinite loops. A user supplied clean up routine may be specified if necessary. MASM 5.1/TASM 2.0 - C callable installation & de-installation functions. Language & memory model independant. Change the .model directive as needed. Author: David Burki --------------------------------------------------------- END OF COMMENT ~ title BREAKOUT.ASM page 57,132 % .model m_model, lang ; ---- MACROS and EQUATES ---- ;macro to simulate an interrupt so the interrupt returns ;to the instruction immediately following the call sim_int macro num pushf call cs:orig_&num endm ;macro to push selected registers apush macro a,b,c,d,e,f,g,h irp x,<a,b,c,d,e,f,g,h> ifnb <x> push x endif endm endm ;macro to pop selected registers apop macro a,b,c,d,e,f,g,h irp x,<h,g,f,e,d,c,b,a> ifnb <x> pop x endif endm endm ;macro to install a replacement vector ; -- assumes that ds = code seg of replacing function ; -- all var names used to save original vector must be ; 2 characters long plus a training "h" (i.e. for ; int 8h "orig_08h") install_vector macro vector_num,function_name mov ax,35&vector_num int 21h mov word ptr orig_&vector_num,bx mov word ptr orig_&vector_num+2,es lea dx,function_name mov ax,25&vector_num int 21h endm ;macro to un-install a replaced vector ; -- all var names used to save original vector must be ; 2 characters long plus a training "h" (i.e. for ; int 8h "orig_08h") restore_vector macro replaced_vector lds dx,cs:orig_&replaced_vector mov ax,25&replaced_vector int 21h endm ; segment and offset of the BIOS break flag BIOS_SEG equ 40h BREAK_FLAG_OFF equ 71h ; ---- CODE ---- .code ; declare externally visible functions public insure, cancel ; NOTE: all variables used here are part of the code ; segment so the interrupt routines can have easy ; access to them ; --- storage for the address of the InDOS flag indos_addr dd 0 ; --- storage for the address of the critical error flag critter_addr dd 0 ; --- storage for the version of dos dos_major_version db 0 dos_minor_version db 0 ; --- flag indicating disk i/o in progress busy_flag db 0 ; --- far pointer to clean up routine exit_routine dd 0 ; --- storage for original addresses of intercepted ; interrupt vectors. orig_08h dd 0 orig_1bh dd 0 orig_13h dd 0 orig_25h dd 0 orig_26h dd 0 ; --- storage for the segment addr of the psp of process ; that asked for insurance - if zero, insurance isn't ; in effect insured_psp dw 0 ; --- flag if still processing in int 8h in_already db 0 ; --- interrupted program's SS & SP save_ss dw 0 save_sp dw 0 ; --- original C stack segment installer_ss dw 0 installer_sp dw 0 ; --- local stack while in int_8h_handler my_stack dw 256 dup(0) stack_top label word assume ds:@curseg, es:nothing ;--------------------------------------------------------- ; GET_DOS_VERSION() ; Obtain the version & revision of DOS. Store the version ; in the variable "dos_major_version" and the revision in ; the variable "dos_minor_version". Both variables are code ; segment variables. ; ; Returns: ; AL - dos minor version number ; AH - dos major version number ;--------------------------------------------------------- public get_dos_version get_dos_version proc mov ah,30h int 21h mov cs:dos_major_version,al mov cs:dos_minor_version,ah ret get_dos_version endp ;--------------------------------------------------------- ; GET_CRITICAL_ERROR_ADDR() ; This function obtains & saves the address of the ; critical error flag. For DOS versions 3+, the critical ; error flag is the byte just before the InDOS flag. For ; DOS 2.x, it's the byte just after. ; ; NOTE: get_dos_version() must be called before this ; function ; ; NOTE: For COMPAQ DOS version 3.x, the critical error ; flag is located 01aah bytes BEFORE the InDOS flag. ; ; Trashes: AX ;--------------------------------------------------------- public get_critical_error_addr get_critical_error_addr proc USES ES BX ; --- get the address of the InDOS flag mov ah,34h int 21h ; --- dos 3.x or better use byte before InDOS cmp byte ptr cs:dos_major_version,3 jge byte_before ;good_version ; --- dos 2.x, use byte after InDOS flag inc bx jmp store_critter_addr byte_before: dec bx store_critter_addr: ; --- save the address & return success mov word ptr cs:critter_addr,bx mov word ptr cs:critter_addr+2,es ret get_critical_error_addr endp ;--------------------------------------------------------- ; GET_INDOS_ADDR() ; Uses the undocumented (but well known) function 34h of ; INT 21h to obtain a far pointer to the "InDOS" flag. ; Stores the address of the flag in the code segment ; variable "indos_addr". ; ; Trashes AX ;--------------------------------------------------------- public get_indos_addr get_indos_addr proc USES ES BX ; --- get the address mov ah,34h int 21h ; --- save address in cs referenced variable mov word ptr cs:indos_addr,bx mov word ptr cs:indos_addr+2,es ret get_indos_addr endp ;--------------------------------------------------------- ; CHECK_CRITTER_FLAG() ; Examine the undocumented "critical error" flag to ; determine if a critical error is in progress. ; ; Returns: ; carry clear - A critical error is NOT in progress ; carry set - A critical error is in progress ;--------------------------------------------------------- public check_critter_flag check_critter_flag proc USES AX DS SI ; --- ds:si <- address of critter flag lds si,dword ptr cs:critter_addr ; --- check critter flag = zero lodsb or al,al jz no_critter ; --- critter flag not zero, return carry set stc jmp critter_exit ; --- critter flag zero, return carry clear no_critter: clc critter_exit: ret check_critter_flag endp ;--------------------------------------------------------- ; CHECK_INDOS_FLAG() ; Examine the undocumented "InDOS" flag to determine if ; non-rentrant DOS functions are currently executing. ; ; Returns: ; carry clear - InDOS flag is zero. ; carry set - InDOS flag is non-zero. ;--------------------------------------------------------- public check_indos_flag check_indos_flag proc USES AX DS SI ; --- ds:si <-- addr of InDOS flag, then load al with ; the byte at that address lds si,dword ptr cs:indos_addr lodsb ; --- indos flag equal zero, DOS is stable or al,al jz dos_stable ; --- no, set carry & return stc jmp indos_exit ; --- yes, clear carry and return dos_stable: clc indos_exit: ret check_indos_flag endp ;--------------------------------------------------------- ; CHECK_BREAK_BIT() ; This function examines the BIOS Break Flag (bit 7 of ; the byte at 40:71). ; ; Returns: ; carry clear - Break Flag is clear. ; carry set - Break Flag is set. ;--------------------------------------------------------- check_break_bit proc USES DS ES BX ; --- establish addressing to the flag mov bx,BIOS_SEG mov es,bx mov bx,BREAK_FLAG_OFF ; --- is bit 7 set test es:byte ptr [bx],10000000b jnz break_bit_set ; --- no, return with carry clear clc jmp check_break_exit ; --- yes, clear it & return carry set break_bit_set: and es:byte ptr [bx],01111111b stc check_break_exit: ret check_break_bit endp ;--------------------------------------------------------- ; INSTALL_INTERCEPTS() ; Retrieve & save the current vectors, replacing the ; vector table entries with the addresses of the ; intercept routines. ; Entry: ; DS = CS ; Returns: ; No value ; Trashes: ; AX, BX, DX, ES ;--------------------------------------------------------- install_intercepts proc assume ds:@curseg ; --- capture int 8h vector install_vector 08h,int_8h_handler ; --- capture int 13h vector install_vector 13h,thirteen_handler ; --- capture int 25h vector install_vector 25h,twenty_five_handler ; --- capture int 26h vector install_vector 26h,twenty_six_handler ; --- capture int 1bh vector install_vector 1bh,break_handler ret install_intercepts endp ;--------------------------------------------------------- ; INSURE( cleanup_function ) ; void (*PFV)(); /* far pointer to cleanup function */ ; ; Installs the breakout tool. ; ; Returns: ; AX = zero - installed successfully ; AX not zero - did not install ;--------------------------------------------------------- insure proc USES DS ES SI DI, CLEAN_UP:FAR PTR ; --- force ds = cs push cs pop ds assume ds:@curseg ; --- currently in palce? cmp word ptr insured_psp,0 ; --- yes, return to caller with no action jnz not_installed ; --- get dos version call get_dos_version ; --- if not dos 3.x don't install cmp ah,3 jl not_installed ; --- retrieve & save the psp of the current process ; --- function 62h (get PSP) is DOS 3+ only mov ah,62h int 21h mov insured_psp,bx ; --- get the addr of clean up function & save it les bx,CLEAN_UP mov word ptr exit_routine+2,es mov word ptr exit_routine,bx ; --- get the addr of "InDOS" flag call get_indos_addr ; --- get the gritical error flag address call get_critical_error_addr ; --- install the interrupt intercepts call install_intercepts ; --- insure BIOS break flag is clear mov bx,BIOS_SEG mov es,bx mov bx,BREAK_FLAG_OFF and es:byte ptr [bx],01111111b ; --- save installer's SS and SP mov installer_ss,ss mov installer_sp,sp ; --- set good return code & clear "in already" flag ; for int 8h handler xor ax,ax mov byte ptr in_already,al jmp insure_exit not_installed: mov ax,1 insure_exit: ret insure endp assume ds:nothing ;--------------------------------------------------------- ; CANCEL() ; Restore the original vectors and clear the ; "insured_psp" address. ; Returns: ; No value ; Trashes: ; AX ;--------------------------------------------------------- cancel proc USES DS DX ; --- if not installed, get out with no action mov dx,cs:insured_psp or dx,dx jz no_cancellation ; --- get the original int 8h & restore it restore_vector 08h ; --- get the original int 1bh & restore it restore_vector 1bh ; --- get the original int 13h & restore it restore_vector 13h ; --- get the original int 25h & restore it restore_vector 25h ; --- get the original int 26h & restore it restore_vector 26h ; --- clear the insured_psp address mov cs:word ptr insured_psp,0 no_cancellation: ret cancel endp assume cs:@curseg ;--------------------------------------------------------- ; INT_8H_HANDLER() ; Intercept for timer tick interrupt. ; Checks the BIOS break flag (bit 7 at 40:71) on each ; invocation. ; Flagged to prevent rentry. ;--------------------------------------------------------- int_8h_handler proc far ; --- let int 8 do it's stuff sim_int 08h cli ; --- if int 8 post processing is still going on, don't ; re-enter - return to the interrupted code cmp cs:byte ptr in_already,1 jnz do_break_ck iret do_break_ck: ; --- flag that we're processing an int 8h & swap stacks mov cs:byte ptr in_already,1 mov cs:save_ss,ss mov cs:save_sp,sp push cs pop ss mov sp,offset cs:stack_top sti apush ax,bx,cx,dx,ds,es,si,di ; --- if the BIOS break flag is NOT set, iret to caller call check_break_bit jnc no_break ; --- if disk i/o in progress, iret back to caller cmp cs:busy_flag,0 jnz no_break ; --- if not in dos or critical error call check_indos_flag jc no_break call check_critter_flag jc no_break ; --- if the psp of the caller isn't the same as ; the psp when installed, skip it mov ah,62h int 21h cmp bx,cs:insured_psp jnz no_break ; --- BIOS break flag was set, everything is stable and the ; active PSP is the same as the one that installed the ; insurance. clear the BIOS break bit and uninstall ; the intercepted vectors call cancel ; --- if a user supplied exit routine is installed, do it mov bx,word ptr exit_routine+2 or bx,bx jnz do_user_supplied_exit ; --- otherwise, DOS terminate function - error level = 1 mov ax,4c01h int 21h do_user_supplied_exit: ; --- get back BX & ES plus clean off CS, IP & FLAGS pushed ; on original interrupt, then jump to user exit routine mov ss,cs:installer_ss mov sp,cs:installer_sp jmp cs:exit_routine no_break: ; --- clean up the stack apop ax,bx,cx,dx,ds,es,si,di cli mov ss,cs:save_ss mov sp,cs:save_sp sti mov cs:byte ptr in_already,0 skip_it: ; --- iret to the int 8 caller iret int_8h_handler endp ;--------------------------------------------------------- ; BREAK_HANDLER() ; Simple replacement for int 1bh - no more than an iret ; to keep the "^C" off the display screen. ;--------------------------------------------------------- break_handler proc far iret break_handler endp ;--------------------------------------------------------- ; THIRTEEN_HANDLER() ; intercept for int 13h ; Increments the busy flag on entry, calls the original ; interrupt service routine, and decrements the busy flag ; when the disk routine is complete. The busy flag must ; be zero to indicate no disk i/o in progress. ;--------------------------------------------------------- thirteen_handler proc far pushf inc cs:busy_flag popf sim_int 13h pushf dec cs:busy_flag popf iret thirteen_handler endp ;--------------------------------------------------------- ; TWENTY_FIVE_HANDLER() ; intercept for int 25h ; Increments the busy flag on entry, calls the original ; interrupt service routine, and decrements the busy flag ; when the disk routine is complete. The busy flag must ; be zero to indicate no disk i/o in progress. ;--------------------------------------------------------- twenty_five_handler proc far pushf inc cs:busy_flag popf sim_int 25h pushf dec cs:busy_flag popf iret twenty_five_handler endp ;--------------------------------------------------------- ; TWENTY_SIX_HANDLER() ; intercept for int 26h ; Increments the busy flag on entry, calls the original ; interrupt service routine, and decrements the busy flag ; when the disk routine is complete. The busy flag must ; be zero to indicate no disk i/o in progress. ;--------------------------------------------------------- twenty_six_handler proc far pushf inc cs:busy_flag popf sim_int 26h pushf dec cs:busy_flag popf iret twenty_six_handler endp end