Magnum One/Magnum One (Mid-American Digital) (Disc Manufacturing).iso/d12/trace122.arc/TRACE.DOC

Text File | 1987-04-19 | 9.5 KB | 211 lines

                     TRACE - Interrupt Tracer version 1.22

                          Written by Joan Riff for:
                     Computerwise Consulting Services

                 P.O. Box 813, McLean VA 22101  [phone]

               Documented and Enhanced By A. B. Krueger

        Contact: ARNY KRUEGER at the EXEC-PC BBS in Shorewood Wisconson.
                                  414-964-5160


TRACE is a TSR program that traces interupts.

                It:

                 * traps interrupt's
                 * traces the registers at the entry to the interrupt,
                 * executes the interrupt itself
                 * optionally traces the registers at exit from the interrupt.

TRACE also allows the user at the keyboard to display  this traced
information, either on the screen or at the printer.

The interrupts that are to be TRACEd are specified in the ICT table in
the source code. Once defined, they may be enabled or disabled from the
keyboard.  A default ICT is provided and you should not modify it until
you understand how TRACE is used and how it works.

      <<< REBOOT AS SOON AS POSSIBLE AFTER INVOKING TRACE!!! >>>

TRACE is not foolproof or bugfree. Use it as a tool for finding out what
DOS and DOS programs do. USE IT AT YOUR OWN RISK.  When you have a print
out of the trace activity that interests you, reboot your system.  It may
not be long for this world! Don't say that you weren't warned.


      Usage is: TRACE [size]

          where: size is the size of the trace table in K
                 between 10 and 53, default is 30


Known problems:

   *   Programs that use:  INT 21h function E0h. Trace uses it for
       avoiding repeated installation within a single booted session.

   *   Programs that use INT 2Eh. They mess with DOS's mind anyway.

   *   Keyboard ICT control for ICT's 7-15 isn't there. I added ICT's
       7-15 to make TRACE stable, but it will take some major work to
       get them to be keyboard controllable. Send mail if you need this
       feature - I would never use it.

   *   Print spoolers. TRACE does OUT's to the Parallel port as well
       as the more usual BIOS INT 17's.


How it works:

   TRACE initialization code is in TRACE12.ASM.  At initialization, TRACE
   initializes its Interrupt Control Table (ICT).  The ICT contains one
   element for every interrupt number or subset thereof to be traced.

   Tracing control within a given interrupt number is determined by the
   value of AH. Interrupts vary as to whether they return to the caller,
   or not. INT 20 (program exit) is an example of an interrupt that does
   not return to the caller. Treatment of the 808x flags at return also
   varies, and is controlled by the ICT. DOS INT 21 function 25 is used
   to route interrupts to TRACE entry points.

   The ICT entries are laid out in TRACE1E.AIC, and defined in
   TRACE1.ASM.  Further documentation about  ICT's is located there, for
   easy reference.  There are 16 possible different ICT entries. The
   first 12 are used, leaving 4 for future expansion. The first 12 are
   not sacrosanct, but an entry covering INT 21H  0D0h < AH < 0FFh is
   recommended. TRACE traps  INT 21h to protect itself against being
   loaded twice.

   TRACE allocates a trace table in accordance with the calling
   parameter. If none is provided, 30K is used as a default. The trace
   table size is forced to be between 10K and 64K. If below 10K, the
   table would be smaller than the program that controls it, which makes
   little sense. The 64K limit comes from the 808x segment size.

   When a interrupt to be TRACEd takes place, TRACE stores register and
   flag information in the trace table, with a header that tells what
   kind of interrupt trace entry this is. If post-interrupt tracing is
   requested, then some carry-forward information is placed on the stack,
   and control is passed to the interrupt handler that was in place when
   TRACE was initialized. After the original interrupt handler returns,
   TRACE stores stores register and flag information in the trace table,
   with a header that tells what kind of interrupt trace entry this is.
   If the interrupt table is full, tracing ends.

   When TRACE is entered via Shift-PrtSC, or from Periscope via INT 60h,
   TRACE's command processor prompts for output and trace control
   commands, which are single letters. One important command is "Q" for
   QUIT, which returns control to DOS. The Output routing options are
   printer or screen. Print output enables displaying TRACE data without
   affecting the screen's display, as well as making hard-copy for
   reference. The enable and disable options allow the status of
   individual ICT's to be altered.


      Command Summary - enter via Shift-PrtSc:

      C        Clears the trace table and ICT count fields.
      L        Lists the ICT status, include INT counts.
      P        Causes Trace output, including command mode menus,
               to go to the printer
      S        Causes Trace to use Screen output (Default)
      T        Lists the trace, or selected data, by ICT number.
      W        Calls the old Prt-Sc handler.

   The ICT for INT 21h subfunctions 00-09 are usually disabled because
   there is a lot of uninformative action in this range, for keyboard and
   screen I/O. It would not be too wise to try to trace INT 5h, 10h and
   17h, as they are used by TRACE.


How and Why to Modify TRACE:

   When TRACE displays trace table data, it is formatted and self-
   explanitory. You may not like my explanations, or want to add some
   more.

   Each known interrupt is tagged with identifying text, and the register
   and flag contents are labeled and described. Tables in TRACE1.AIC
   control this for interrupts 13H and 21h.  TRACE11.ASM contains most of
   the formatting subroutines and secondary tables.

   Note that TRACE11 contains a PRINT_EDIT subroutine that is capable of
   sophisticated output formatting using flag bytes EDIT_xxxx, which are
   defined in TRACE1E.AIC.

   TRACE1E.AIC changes can affect all three .ASM files. If you change
   TRACE1E, figure on re-assembling TRACE1, TRACE11, and  TRACE12.
   Normally, updating the TRACE1 ICT definitions necessitates re-
   assembling only TRACE1. Link TRACE using the command:

               LINK TRACE1+TRACE11+TRACE12,TRACE;

   Convert TRACE to a COM file using:

               EXE2BIN TRACE.EXE TRACE.COM


How to use TRACE:

   Initialize TRACE using the command:

                    TRACE

   If TRACE is already in place it will type an error message, but no
   harm will be done. Errorlevel 10 will be set if it is already in
   place.

   When you TRACE, we encourage you to use the Shift-PrtSc key to
   interrupt the opeation of complex programs, and clear the trace table
   so that the contents of the trace table are relevant to your study.
   Some programs trap INT 5, and will keep you from getting into TRACE
   using Shift-PrtSc, until they complete. Trace uses the PrtSc anti-
   recursion byte at 500h. Any program that sets this byte to 1 will keep
   Trace from going into command mode.

   TRACE has been upgraded to be fairly stable. In its original form
   Interuupts 20h, 27h, 21h with AH=31h and 21h with AH=4Ch would cause
   it to crash often.  It is your responsibility to alter the operational
   environment or modify TRACE to stay intact through the operation you
   are TRACing.

   TRACE will impact the performance of  your PC when it is running,
   especially if the trace table is not yet full.

   TRACE provides a means for understanding the control and flow of
   programs like DOS itself, for which you have no source code or
   internals documentation. One trick is to use TRACE  CS:IP values to
   get a IP value that you subsequently use with DEBUG to trace the area
   of interest.

   Trace information can also be used to find out which program code
   inspects or updates specific parts of a disk that are known to contain
   information of interest.  You may have to work back from an INT 13 or
   INT 24 entry to do this.  You will have to identify the location on
   disk by drive, side, track, and sector number. There are several disk
   utilities that will help you do this such as NORTON's utilities, IBM's
   DiskRepair, or Central Point's PC TOOLs.

   When running TRACE, you may notice a large number of DOS INT 21h AH=3E
   calls as DOS closes file handles 5-19 once per keyboard or .BAT file
   command.  If this bothers you, you can modify the ICT table to disable
   TRACEing this interrupt. Note that there is one pass through TRACE's
   interrupt handlers for every different range of AH you define in the
   ICT's, until the correct ICT is found.

   Any insights about TRACE that you route to the author will be
   appreciated! Contact ARNY KRUEGER at the EXEC-PC BBS (414-964-5160),
   or daytime voice phone [phone].


Trace update history:

    1.21 1/26/87  - first released modified version

    1.22 2/13/87  - Corrected trace table size option processing
                  - re-instated PrtSc function via main menu