A debugger for SAIL - The Stanford University InfoLab
Contents
1. A list of options including short descriptions of the procedures described in this section is printed A question mark followed by a carriage return is interpreted as a call to HELP 46 SETLEX PROCEDURE SETLEX level Evaluating SETLEX n changes the static lexical scope to the scope of the n th entry in the dynamic scope list SETLEX O is the scope of the breakpoint SETLEX 1 is the scope of the most recent procedure call in the dynamic scope etc 47 SHOW STRING PROCEDURE SHOW first last 0 The text of the program from the source or listing file If last is less than first then set last to last first Return coordinates first through last SHOW 5 3 gives coordinates 5 6 7 and 8 SHOW 5 7 gives coordinates 5 6 and 7 SHOW 5 gives coordinate 5 only A plus sign following the coordinate number indicates that the values of some variables have been carried over in accumulators from the previous coordinate Changing the value of variables might not be successful in such a case because BAIL will not change any accumulator value directly The MEMORY construct can be used to modify any location in a core image including the accumulators 48 TEXT STRING PROCEDURE TEXT The current static and dynamic scopes with text from the source or listing file 17 BAIL A debugger for SAIL RUN TIME ACTION 4 9 TRACE PROCEDURE TRACE procedure Special breakpoints are inserted at the beginning and end of th2. eTEST I SAV 1 Initialization uses file created last time BAIL ver 18 May 75 using TEST1 BAI End of BAIL initialization Switch 27B at compile time makes SAIL predeclared runtime routines known to BAIL 1 OPENFILE NULL W TODAY TMP 4 1 OUT 4 TH IS IS A TEMPORARY FILE CREATED WHILE IN BAIL 1 CFILE 4 F 1 OPENFILEC RC TODAY TMP OLD VERSION 4 1 SINI 4 200 Z THIS IS A TEMPORARY F IL CREATED WHILE BAIL ODTIM 1 15 SATURDAY HAY 10 1975 17 13 23 Quickie review of BAIL capabilities 1 EXPRESS ION PROCEDURE CALL TRACE PROCEDURE UNTRACE PROCEDURE BREAK PROCEDURE BLOCK OR LABEL UNBREAK PROCEDURE BLOCK OR LABEL 60 SETLEX LEVEL TEXT ARGS HELP DDT 1 TC End of the examples 12 un BAIL A debugger for SAIL COMPILE TIME ACTION SECTION 3 COMPILE TIME ACTION The principal result of activating BAIL at compile time is the generation of a file of information about the source program for use by the run time interpreter This file has the same name as the REL file produced by the compilation except that the extension is SM 1 If requested BAIL will also generate some additional code for SIMPLE procedures to make them more palatable to the run time interpreter The action of BAIL at compile time is governed by the value of the B switch passed to the compiler If the value of this switc
3. is a true block and not just a compound statement but does not have a name then BAIL will invent one The name is of the form Bnnnn where nnnn is the decimal value of the current coordinate 14 BAIL A debugger for SAIL RUN TIME ACTION SECTION 4 RUN TIME ACTION The BAIL run time interpreter is itself a SAIL program which resides on the system disk area This program is usually loaded automatically and does some initialization when entered for the first time The initialization generates BAI file of information collected from the SMI files produced by separate compilations if any The SM1 files correspond to REL files and the file corresponds to the DMP or SAV file Like RPG or CCL BAIL will try to bypass much of the initialization and use an existing O Al file if appropriate During initialization BAIL displays the names of the SM1 files it is processing For each SM1 file which contains program counter text index information BAIL displays the names of the text files and determines whether the text files are accessible The interpreter is activated by explicit call previously inserted breakpoints or the SAIL error handler For an explicit call say EXTERNAL PROCEDURE BAIL BAlL From the error handler respond B Breakpoints will be described later in this section 41 Debugging Requests When entered BAIL prints the debugging recursion level followed by a colon and awaits a debugging request BA
4. Approach to Interactive Programming Systems Ph D thesis Computer Science Department Stanford University August 1974 4 Kurt VanLehn ed SAIL USER MANUAL Stanford Artificial Intelligence Laborat ory memo AIM 204 Computer Science Department report STAN CS 73 373 July 1973 24
5. D CELL CY NEW RECORD CELL CELL CAR CX NULL RECORD CELL CX NULL RECORD CELL CAR CY CX CELL CDR CY NULL RECORD P 1 SUNDAY P 2 MONDAY Le SUNDAY DATUM SUNDAY 0 DAY SUNDAY Q amp MONDAY Se QQ 1 SUNDAY MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY S2 MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY S3 MONDAY WEDNESDAY FRIDAY S4e SATURDAY SUNDAY SSe SUNDAY FR I DAY FOREACH DAY SUCH THAT DAY IN S1 DO MAKE DAY XOR SUNDAY EQV SATURDAY BAIL USERERR 8 1 THIS IS A TEST END TEST EXIT EXECUTE TEST2 SAI 27B SAIL TEST2 1 LOADING LOADER 15K CORE 25K MAX 153 WORDS FREE EXECUTION BAIL VER 10 MAY 75 TEST2 SM1 TEST2 SAI END OF BAIL INITIALIZATION L SUNDAY 10 BAIL A debugger for SAIL gt Ea e RS Pa L3 LE 1 54 SUNDAY SATURDAY S5 SUNDAY FRIDAY S4UNION S5 SUNDAY FRIDAY SATURDAY FRIDAY IN 84 8 S2 LEQ S2 1 DAY SATURDAY DATUM DAY 0 CELL 9231 CELL CAR CX J NULL RECORD CELL CAR CY CELL 9231 SUNDAY ASSOC SATURDAY SUNDAY SUNDAY EQV SATURDAY SUNDAY MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY SUNDAY SATURDAY PHI en EQV SUNDAY 1 EXAMPLES BAIL A debugger for SAIL EXAMPLES Go back to the earlier example
6. DT after a push down overflow or a string garbage collection error will get you into trouble SIMPLE procedures cause headaches for BAIL because they do not keep a display pointer Indeed the compiler gets lost in the following example and does not complain BEGIN LOST PROCEDURE A INTEGER I BEGIN A SIMPLE PROCEDURE B OUTSTR THE VALUE OF IIS CVS I PROCEDURE C INTEGER B C 2 END A 1 END LOST BAIL tries valiantly to do the right thing but occasionally it also gets lost BAIL will try to warn you if it can In general looking at value string parameters of SIMPLE procedures does not work 20 BAIL A debugger for SAIL RESOURCES USED SECTION 5 RESOURCES USED Compile time A One channel This means that REQUIREd source files may only be nested to a depth of about 9 B Memory Up to 1 1 maximum lexical nesting depth more words of memory may be required compared with previous compilations C CPU time Approximately 0 3 seconds per page of dense text ll Run t ime A Channels Three during initialization two thereafter Channels are obtained via GETCHAN B BAIL uses 7 of the privileged breaktables obtaining them via GETBREAK C REQUIRE 64 STRING PDL Necessary if the debugging recursion level will exceed 3 or 4 D Memory 9 5K of coordinates 127 DIV 128 2 of blocks 5x of symbols words E CPU time 1 Initialization Typically 4 s
7. EDURE BREAK location condition NULL act ion NULL count 0 BREAK inserts a breakpoint The syntax for the first argument is lt location gt lt label gt lt procedure gt lt block name gt lt nnnn gt block name gt lt delim gt lt location gt deli m gt lt any character not legal in an identifier nnnn decimal coordinate number If the location is specified by the block name gt lt delim gt lt location gt construct then the blocks of the core image are searched in ascending order of address of BEGINs until the first block name is matched The search continues until the second block name is matched etc The breakpoint is inserted at the label procedure or coordinate declared within the scope of the last block name This detailed specification is not usually necessary as shown in the examples The last three parameters are default able and need not be specified again as in the examples The action taken at a breakpoint is IF LENGTH condi t ion AND EVAL condi t ion AND count count 1 lt 0 AND LENGTH action THEN EVAL acti on EVAL TTY Here EVAL is a procedure which evaluates its string argument and returns the value of the last expression evaluated similar to PROGN in LISP 44 DDT PROCEDURE DDT This procedure transfers control to an assembly language debugging program if one was loaded 16 BAIL A debugger for SAIL RUN TIME ACTION 45 HELP PROCEDURE HELP
8. IL accepts ALGOL and LEAP expressions of the SAIL language A complete description is given in 4 and in the addenda describing the syntax of records and record pointers The following exceptions should be noted Expressions involving control structure are not allowed hence BAIL will not recognize AND CR IF THEN ELSE or CASE Bracketed triple items are not allowed The TO and FOR substring and sublist operators have been extended to operate as array subscript ranges FOR PRINT OUT ONLY If FOO is array then FOO 3 TO 7 will act like FOO S FOO 4 FOO 5 FOO 6 FOO 7 but is easier to type This extension is for print out only no general APL syntax or semantics are provided BAIL evaluates symbolic names according to the scope rules of ALGOL extended to always recognize names which are globally unique and have a fixed memory location everything except parameters and recursive locals For any activation of BAIL the initial scope is the ALGOL scope of the statement from which BAIL was activated The procedure SETLEX see below may be used to change the scope to that of any one of the links in the dynamic activation chain Several procedures are predeclared in the outermost block to handle breakpoints and display information These are described individually below BAIL A debugger for SAIL RUN TIME ACTION 416 ARGS STRING PROCEDURE ARGS The arguments to the procedure which was most recently called 43 BREAK PROC
9. Stanford Artificial Intelligence Laboratory Memo AIM 270 Computer Science Department Report No STAN B 75 523 BAIL debugger for SAIL by John F Reiser Research sponsored by Advanced Research Projects Agency ARPA Order No 2494 and National Science Foundation October 1975 Stanford Artificial Intelligence Laboratory October 1975 Memo AIM 270 Computer Science Department Report No STAN B 75 523 BAIL A debugger for SAIL by John F Reiser ABSTRACT BAIL is a debugging aid for SAIL programs where SAIL is an extended dialect of ALGOL60 which runs on the PDP 10 computer BAIL consists of a breakpoint package and an expression interpreter which allow the user to stop his program at selected points examine and change the values of variables and evaluate general SAIL expressions In addition BAIL can display text from the source file corresponding to the current location in the program In may respects BAIL is like DDT or RAID except that BAIL is oriented towards SAIL and knows about SAIL data types primitive operations and procedure implementation The work retorted here was funded in part by a National Science Foundation graduate fellowship Computer facilities provided by Stanford University under the Advanced Research Projects Agency ARPA Contract DAHCI5 73 C 0435 and by Institute for M athematical Studies in the Social Sciences at Stanford T he views and conclusions contained i
10. This feature of SAIL is cast in concrete and will not be changed As a result the following DOES NOT WORK unless special precautions are taken BEGIN EXTERNAL PROCEDURE BAIL EXTERNAL PROCEDURE PLOT REAL X0 Y0 X1 Y 1 REQUIRE CALCOM LIBRARY BAIL END PLOT will not be defined by SAIL hence BAIL will not know about it However if there 22 BAIL A debugger for SAIL CURRENT STATUS are any references to PLOT real or dummy calls then BAIL will know The following trick can also be used assuming that CALCOM is a SAIL compiled procedure Compile CALCOM with 108 which says make the SM 1 file but don t automatically load SYS BAIL REL Then the above will win due to BAIL recognizing things which are globally unique and programs which do not use BAIL will not have it loaded just beacuse the library was used This same problem occurs with EXTERNAL RECORDICLASS declarations Use of the subfield index information does not cause a reference to the class name but NEW RECORD does Thus the same 10B trick must be used if there are no NEW RECORD calls 23 BAIL A debugger for SAIL CURRENT STATUS REFERENCES 1 DECsystem10 Assembly Language Handbook DEC 10 NRZC D Digital Equipment Corporation Maynard Massachusetts 1973 2 Edwin H Satterthwaite J r Source Language Debugging Tools Ph D thesis Computer Science Department St anford University May 1975 3 Daniel C Swinehart COPILOT A Multiple Process
11. and TEXT this would ordinarily create confusion so they are handled specially When these procedures are evaluated they set a flag which inhibits quotation mark fiddling provided that no further evaluation takes place before the next typeout Thus SHOW 5 3 will be typed plain but STR SHOW 5 3 will have quotation marks massaged 4 17 BAIL and DDT If BAIL is initialized in a core image which does not have DDT or RAID then things will be set up so that the monitor command DDT gets you into BAIL in the right way That is BAIL will be your DDT To enter BAIL from DDT provided that the SAIL initialization sequence has already been performed use pushi P lt program counter X JRST BAILSX For example if J BOPC contains the program counter PUSH P JBOPCSX 19 BAIL A debugger for SAIL RUN TIME ACTION JRST BAILSX The entry B provides a path from DDT to BAIL which works whether or not the core image has been initialized One use of this feature is to BREAK a procedure in an existing product ion program without recompiling For example PROG originally compiled loaded with BAIL and DDT and SAVEd GET PROG DD B G BAIL initialization 1 BREAK procedure 1 160 G To enter DDT from BAIL simply say DDT For operation under TENEX control B is a pseudo interrupt character which gets you into BAIL 4 18 WARNINGS Since BAIL is itself a SAIL procedure entering BAIL from the error handier or O
12. atic and dynamic scope of the current breakpoint display selected statements from the source program allow escape to an assembly language debugging program and cause resumption of the suspended main program These procedures are described in the technical portion of the manual The following examples illustrate many of the features available in BAIL Text was recorded from an actual session on the computer BAIL A debugger for SAIL EXAMPLES SECTION 2 EXAMPLES This is a test program run on TENEX eTY PE TEST I1 SAI REISER TEST1 SAI 1 SAT 10 MAY 75 2 37PM PAGE 1 BEGIN TEST EXTERNAL PROCEDURE BAIL INTEGER I J K STRING R EA b Y i INTEGER ARRAY 0010 151 STRING ARRAY STRARR 1 5 2 6 INTEGER I TEMVAR DAY I TEMVAR QQ NTEGER PROCEDURE ADD INTEGER J BEG1N ADD DUTSTR GLAD YOU STOPPED BY RETURN 1 J END ADD RECURS I VE INTEGER PROCEDURE FACT INTEGER N FACT RETURN IF N LEQ 1 THEN 1 ELSE NxFACT N 1 END FACT SIMPLE PROCEDURE S MPROC REFERENCE I NTEGER BEG IN ADD M Me32 END SBEG FOR Ie8 STEP 1 UNTIL 15 DO FOO IJeIxI FOR 1 1 STEP 1 UNTIL 5 DO FOR Je2 STEP 1 UNTIL 6 DO STRARR 1 3 e64 8x J 1 4 Je6 Kelle DEAL Be QED Ce THE LAST PICASSO X 3 14153265 0 2 23 BAIL ADD 7 45 SIMPROC J USERERR 8 1 THIS IS A TEST r END TEST TL BAIL A d
13. e DEC PDP 1 and subsequently extended for use on the PDP 6 and PDP 10 DDT and its derivatives are still among the most powerful tools for debugging assembly language programs BAIL is a high level breakpoint package for use with SAIL programs Swinehart 3 and Satterthwaite 2 contain descriptions of other high level debugging syst ems Communication between the programmer and BAIL is in character strings which are the names and values of SAIL objects BAIL reads general SAIL expressions typed by the programmer evaluates them in the context of the place in the program where execution was suspended and prints the resulting value in an appropriate format The evaluation and printing are performed just as if the programmer had inserted an extra statement into the original program at the point where execution was Suspended BAIL also provides a way to talk about the program to answer the BAIL A debugger for SAIL INTRODUCTION questions Where was execution suspended By what chain of procedure calls did execution proceed to that point and What is the text of the program In order to perform these functions BAIL must have some information about the program being debugged The SAIL compiler will produce this information if the program is compiled with an appropriate value supplied for the B switch See the technical portion of the manual for the exact meaning of the various switch values In these examples the compiler produces two
14. e procedure named On entry the procedure name and arguments are typed On exit the name and value returned if any are typed 410 TRAPS STRING PROCEDURE TRAPS A list of the current breakpoints and traces 4 11 UNBREAK PROCEDURE UNBREAK locat ion The breakpoint at the location specified is removed 412 UNTRACE PROCEDURE UNTRACE procedure The breakpoints inserted by TRACE are removed 4 13 GO pseudoPROCEDURE GO An immediate exit from the current instantiation of BAIL is taken and execution of the program is resumed GO is a reserved word the only one in BAIL 7 18 BAIL A debugger for SAIL RUN TIME ACTION 4 14 GSTEP pseudoPROCEDURE GSTEP Temporary breakpoints are inserted at all of the logical exits of the current statement and execution of the program is resumed Logical exits are the next statement and locations to which the current statement can jump excluding any procedure calls All of the breakpoints which are inserted will be removed as soon as one of them is encountered 4 15 STEP pseudoPROCEDURE STEP Temporary breakpoints are inserted at all locations to which the current statement can jump including procedure calls and execution of the program is resumed 416 STRING TYPEOUT Strings are usually typed so that the output looks the same as the input i e a string is typed with surrounding quotation marks and doubled internal quotation marks For SHOW ARGS
15. ebugger for SAIL EXAMPLES Compile and load with BAIL eSAIL SAV 18 TENEX SAIL 8 1 4 4 75 FOR HELP xTEST1 27 TEST1 SAI 1 1 END OF COMPILATION LOADING LOADER 6 9K CORE EXECUTION Save the core image for later use essavE PAGES FROM 8 TO 577 ON TESTI NEW FILE1 CONF I RM Start the program eSTART BAIL identifies itself and the files involved BAIL VER I8MAY 75 5 1 5 1 2 TEST1 SA1 1 End of BAIL initialization 1 45 The 1 is BAlL s prompt it indicates the level of recursive invocations of BAIL and the fact that BAIL is awaiting input See how constants are entered and printed The 45 lt cr gt is typed by the user and the next line 45 is BAIL s reply 45 1 7 089 7 083000 Ea SOME RANDOM STRING SOME RANDOM STRING An octal constant all printout is decimal 1 75 _ 189 Symbolic constants More than one expression requested 1 u n BAIL A debugger for SAIL EE 4 1 J X 3 141593 1 16146 46 1 1 46 1 1 lt 0 1 1 J 1 1 98 LAND 17 2 1 2 UNKNOWN ID XYZ 1 45 89 4 53 06 1635 300 1 X J 9 141593 1 AD D 3 4 HI GLAD YOU STOPPED BY 1 ADD 3 ADD TAKES 2 ARGUMENTS ADD 3 1 FOO ARRAY 80 151 1 00 4 16 1 FOO 5FOR 3 25 36 49 1 STRARR EXAMPLES Variables assignment Relational operators remember 0 is FALSE An undeclared iden
16. econds for 30 page program 2 Debugging requests 0 07 seconds per simple request DDT response time Ill Disk space A The SMI file for a 78 compilation is typically one fourth the size of the corresponding REL file B The BAI file for a group of 7B compilations is typically one third the total size of the corresponding REL files 21 BAIL A debugger for SAIL CURRENT STATUS SECTION 6 CURRENT STATUS The state of the world is determined by the values of the accumulators and the value of the SAIL variable SKIP The run time interpreter recognizes only the first 15 characters of identifier names the rest are discarded without comment The characters which are legal in identifiers are ABCDEFGHI JKLMNOPQRSTUVWXYZ _ U SU RI te 0123455789 gt 3 8 87 Notable for its absence period LOCATION of a procedure does not work PROPS is read only Bracketed triple items are not allowed A procedure call containing the name of a parametric procedure functional argument is not handled properly Contexts are not recognized The run time interpreter will not recognize macros External linkage If an identifier is never referenced by code i e has an empty fixup chain at the time fixups are put out to the loader then that identifier is not defined by SAIL Thus variables which are never used do not take up space and a request to the loader is not made for EXTERNALS which are not referenced
17. es observed lights and had complete control of the whole machine The programmer could examine and change any location in memory and could start stop and singie ste the processor Console debugging soon became uneconomical on medium and large scale machines It is still used on minicomputers This type of debugging i at t ha machine language level the lights and Switches are direst reprasentatichs of bit inside the machine Debugging moved to the assembly language leveiwith the development of interactive time sharing systems in the early 1960 s The programmer typed commands at a terminal and a collection of special subroutines interpreted the commands so that the effect was similar to working at the console of the machine Instead of communicating in bits the programmer and subroutines used character strings in the format of octal and decimal integers text symbolic machine instructions and symbolic addresses One of the most important features of the debugging routines was the ability to Suspend the execution of the program being debugged enter the debugging routines communicate with the programmer resume execution and make the whole process invisible to the program being debugged This process became known as breakpointing the location where the main program was stopped is a breakpoint and the debugging routines are called a breakpoint package The premier example of a symbolic debugging package is DDT 1 developed for use on th
18. files File PROG REL contains the relocatable code and loader instructions and file PROGSM 1 contains the information for BAIL The PROG SM 1 information consists of the name type and accessing information for each variable and procedure the location of the beginning and end of each statement and a description of the block structure The code for BAIL itself is loaded automatically when the program is loaded order for the added Information and code to be of any use it must be possible to give control to BAIL at the appropriate time explicit call to BAIL is possible by declaring EXTERNAL PROCEDURE BAIL in the program and using the procedure call BAlL This works well if it can be predicted in advance where BAlLing might be helpful Runtime errors such as subscript overflow or CASE index errors are not as predictable but responding B to the SAIL error handler will activate BAIL interrupting the program while it is running to investigate a possible infinite loop for example can be achieved under the TENEX operating system by typing control B a DEC 5 10 operating system first return to monitor mode by typing one or more cont rol C s then activate BAIL by typing DD lt cr gt BAIL performs some initialization the first time it is entered The information in the SM1 file s is collected and processed into a file PROG BAI This new file reflects ail of the information from the 5 1 files of any separately compiled pr
19. from BAIL Leave anot her level of BAIL And come back again Where are we St at ic block structure Dynamic procedure invocations The 4 means coordinate number 4 ADD 4 INTEGER PROCEDURE ADD INTEGER I J TEST 24 ADD 7 45 SIMPROC J USERERR 8 1 1 ARGS BAIL A debugger for SAIL EXAMPLES 45 Remove the breakpoint 1 UNBREAK ADD 1 G0 Output from other calls in the program GLAD YOU STOPPED BY GLAD YOU STOPPED BY THIS IS ATEST CALLED FROM 642124 LAST SAIL CALL AT 400303 TB Entry to BAIL from the error handler 1 TEXT LEXICAL SCOPE DOWN RUNS DYNAMIC SCOPE e i FIRST ROUT I NE E i SIMPLE 642124 44 FILE NOT VIEWABLE TEST 26 USERERR 0 1 THIS IS TEST END T UNKNOWN ID I The static scope needs to be set back one on the dynamic chain 1 SETLEX 1 LEXICAL SCOPE TOP DOWN SRUNS TEST Ie 64 1 C THE LAST PI CASSO 1 CO END OF SAIL EXECUTION BAIL A debugger for SAIL EXAMPLES Leap and records DEC TOPS 10 system TEST2 SAI BEGIN TEST EXTERNAL PROCEDURE BAIL REQUIRE 508 SYSTEM PDL 10 PNAMES LIST L SET S 51 52 53 54 55 INTEGER TEM SUNDAY ITEM MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY INTE GER ITEMVAR DAY ITEMVAR QQ ITEMVAR ARRAY P 1 191 RECORO CLASS CELL RECORD POINTER CELL CAR RECORD POINTER CELL CX CY CX NEW RECOR
20. h is zero the default if no value is specified then BAIL is completely inactive Otherwise the low order bits determine the actions which BAIL performs The value of the B switch is interpreted as octal bit action If this bit is on then the SMI file will contain the program counter to source listing text directory 2 If this bit is on then the SMi file will contain symbol information for ail SAIL symbols encountered in the source If this bit is off then information is kept only for procedures parameters blocks and internals i e non internal local variables are not recorded 4 If this bit is on then SIMPLE procedures will get procedure descriptors and one additional instruction a JFCL 0 which is the fastest machine no op instruction is inserted at the beginning of SIMPLE procedures Except for these two changes all properties of SIMPLE procedures remain the same as before The procedure descriptor is necessary if the procedure is to be called interpretively or if the procedure is to be TRACEd 10 If this bit is on then BAIL will not be automatically loaded and initialized although all other actions requested are performed This is primarily intended to make it easier to debug new versions of BAIL without interfering with SYS BAIL REL By using this switch the decision to load BAIL is delayed until load time 20 If this bit is on then a request to load SYS BAIPDn REL is generated This file contains procedure desc
21. n this document are those of the author s and should not be interpreted as necessarily representing the officia policies either expressed or implied of Stanford University ARPA NSF or the U 5 Government Reproduced in the U S A Available from the National Technical Information Service Springfield Virginia 22151 BAIL A debugger for SAIL TABLE OF CONTENTS TABLE OF CONTENTS SECTION PAGE 1 INTRODUCTION 1 2 EXAMPLES 4 23 COMPILE TIME ACTION 13 4 RUN TIME ACTION 15 Debugging Requests 15 2 ARGS 16 3 BREAK 16 4 DDT 16 5 17 6 17 7 SHOW 17 8 17 9 TRACE 18 10 TRAPS 18 11 UNBREAK 18 12 UNTRACE 18 13 1100 18 14 IGSTEP 19 15 5 19 16 STRING TYPEOUT 19 17 BAIL and DDT 19 18 WARNINGS 20 5 RESOURCES USED 21 6 CURRENT STATUS 22 BAIL A debugger for SAIL INTRODUCTION SECTION 1 INTRODUCTION The ideal way to debug a computer program is to write it correctly in the first place and not debug it at all Experience has shown however that most programs of moderate size contain errors and that debugging is a significant part of software product ion BAIL is a tool which is designed to be useful for interactive debugging of programs written in SAIL 4 a high level ALGOL based language for Digital Equipment Corporation DEC PDP 10 computers In the very early days of computing debugging was done at the console of the computer programmer manipulated switch
22. ograms and the relocation performed by the loader If the core image was SAVEd or SSAVEd then in subsequent runs BAIL will use the BAI file and bypass much of the initialization BAIL prompts the programmer for input by typing a number and a colon The number indicates how many times BAIL has been entered but not yet exited and thus is the recursion depth inside BAIL Input to BAIL can be edited using the standard SAIL input editing characters for the particular operating system under which the program is running BAIL requests input via INCHWL on DEC TOPS 10 systems and via INTTY on TENEX systems input is terminated whenever the editor act ivat es string quotation marks balance and the last character is semicolon otherwise input lines concatenated into one string before being processed further The programmer may ask BAIL to evaluate any SAIL expression or procedure call whose evaluation would be legal at the point at which execution of the program being debugged was suspended except that expressions involving AND OR IF THEN ELSE and CASE are not allowed BAIL evaluates the expression prints the resulting value in an appropriate format and requests further input Declared inside BAIL are several procedures whose values or side effects are useful f A a 2 BAIL A debugger for SAIL INTRODUCTION in the debugging process These procedures handle the insertion and deletion of breakpoints display t he st
23. riptors for most of the SAIL predeclared runtime routines making it possible to call them from BAIL The procedure descriptors and their symbols occupy about 6K The B switch must occur on the binary term not the listing or source term Thus R SAIL or OMPROG 27B PROG 27B PROG 13 BAIL A debugger for SAIL COMPILE TIME ACTION The program counter to source listing index is kept in terms of coordinates The coordinate counter is zeroed at the beginning of the compilation and is incremented by one for each BEGIN ELSE and semicolon seen by the parser provided at least one word of code has been compiled since the previous coordinate was defined Note that COMMENTS are seen only by the scanner not the parser and that DEFINEs and many declarations merely define symbols and do not cause instructions to be generated For each coordinate the directory contains the coordinate number the value of the program counter and a file pointer to the appropriate place The appropriate place is the source file unless a listing file is being produced and the CREF switch is off in which case it is the listing file The listing file produced for CREF is nearly unreadable On a non CREF listing the program counter is replaced by the coordinate number if bit 1 of the B switch is on The symbol table informat ion consists of the block structure and the name access information and type for each symbol If a BEGIN END pair has declarations i e
24. tifier Usable as a desk calculator Procedure call Argument list checking Arrays Array name only gives dimension and subscript bounds information Substring notation has been extended to cover array element s BAIL A debugger for SAIL EXAMPLES ARRAY 1 5 2 6 1 STRARR 1 FOR 2 4 TO 6j Array accesses interpreted 1 FOOf 35 SUBSCRIPTINGERROR INDEX MIN MAX 1 35 8 15 FOO 35 LENGTH LOCATION and MEMORY 1 4 BIG DEAL 1 LENGTH A 8 1 1 46 1 LOCATIONG 118 1 MEMORY 718 64 64 1 15 64 Subst ringing 1 A 2 TO INFJ IG DEAL 1 E 4 Type in must be terminated by a semicolon 1 B QED n Tracing of procedure entry and exit 1 TRACE F ACT 1 F ACT 4 ENTERING FACT 4 ENTERING F ENTERING ENTERING EXITING FACT 1 EXITING FACT 2 EXITING FACT 6 EXITING 24 24 1 UNTRACE C F ACT BAIL A debugger for SAIL 1 FACT 5 120 1 BREAK ADD 1 ADD 3 4 2 ARGS 23 4 2 X 3 21J 4 2 K L 1 2 2 1 G0 HI GLAD YOU STOPPED BY 1 G0 1 TEXT LEXICAL SCOPE TOP DOWN SRUNS TEST ADD DYNAMIC SCOPE MOST RECENT FIRST ROUTINE EXAMPLES Breakpoint ing Now one level deeper in BAIL recursion ARGS prints the arguments list Parameter names evaluate just like variables To exit from one level of BAIL The message is from ADD itself the value 7 is
Download Pdf Manuals
Related Search