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Text File | 1986-01-28 | 25.5 KB | 772 lines

RESOURCE A disassembler for 8080 programs by Ward Christensen CP/M U.G. 1/80 Suggestions? Call me eve's at (312) 849-6279 ---------------- RESOURCE commands are inconsistent at best. - RESOURCE is a kludge based on years of disassembler experience and hacking, and was never "planned" - just coded sitting at a tube, and modified over 2 years before being contributed to the CP/M UG. For example, to kill a symbol: k.label but to kill a control value: caddr,k and to kill a comment: ;addr, but RESOURCE does the job like no other I have seen. ---------------- N-O-T-E: Pardon the editorial, but I feel hardware without good software is useless to 99% of us. Most good software has to be paid for. I strongly support the legitimate purchase of licensed software. I do not regularly use any programs which I have not purchased. (Yes, I do occasionally "try" one, but then buy it if I plan on using it). I have been asked by software businesses to NOT distribute RESOURCE - because of it's ability to produce good .asm source quickly. But, there are so many disassemblers out, why not a good, conversational one? Please use it in the spirit in which it was contributed: to enlarge your understanding of the micro- computer world around you, and to allow you to customize programs which you legitimately own, for your own use. "Semper non rippus offus" ---- NOTE: any command taking a hex address (Dnnnn, etc) may take a value in the form .label but arithmetic may not be performed. (i.e. d.start is ok, but d.start+8 not) ---------------- Overall structure of RESOURCE: It is a .COM file, which runs at 100H. It goes thru 1700 or so, then the stack. At 1800 is a 512 entry table for control commands. Each is 3 bytes long, and controls the format of the re-sourced list, i.e. is it DB, DS, DW, instructions, etc. At 1E00 is the start of the symbol table. It has no defined length as such. If it is not used, it occupies only 2 bytes. If you want to re-source something which is in memory, such as a PROM, a program previously loaded in high memory, "CP/M itself", or whatever, you can just do so. However, typically you want to disassemble a program which runs at 100H, which is were RESOURCE runs. Bob Van Valzah would have solved that by making resource relocatable and moving itself up under BDOS. I wasn't that industrious. Instead, RESOURCE uses the concept of an "invisible" OFFSET. After all, what do you care where it is as long as it LOOKS like it's at 100h? So, you set an offset. O2F00 sets it to 2F00 Hex. Reading a .COM file (RFOO.COM) causes it to come into 3000 on. If you say D100 or L100 it dumps or lists what LOOKS like your program. Internally, RESOURCE is adding the offset to the D and L addresses. What should you set the offset to? Well, that depends upon how many symbols you will use. O1F00 will load the program at 2000, thus allowing only 1E00-1FFF for symbols, i.e. 512 bytes or about 50-60 labels. If you didn't leave enough space, then used B to build a default symbol table, the table could run into and clobber your .com file! (easy recovery, however: just change the offset to being higher, and read in the .COM file again) Each entry takes 3 bytes + the symbol length, and if you like 7 byte labels like I do, that means 10 bytes/label. An offset of 2F00 should be adequate. If you want to put comments into the disassembled program, you will have to designate an area to Use for the comments. The U command (e.g. U4000) specifies what area is to be used. Before issuing the O (offset) command, do: L5 7 which will show the JMP to BDOS, which is the highest memory you may use. (Note if you have, for example, an empty 4K memory board in high memory, you can Use THAT for comments). Let's take an example: You have an 8K file, FOO.COM which you want to disassemble. It will have about 300 labels. 300 x 10 is 3000, or call it 4K (what's a K unless your tight). The symbol table starts at 1E00. 4K more is 2E00. Let's load the .COM at 2E00, so since it normally starts at 100H, the offset is 2D00. O2D00 is the command. We then RFOO.COM to read it in. It says 4E00 2100 which means it came into actual memory to 4E00, but 2100 if we are talking with respect to loading at 100. Thus, we could set our comments table up after the .COM program - say at 5000: U5000 The ? command shows the memory utilization for control, symbol, and comments entries. (no, I never put in anything to keep track of the .COM - you'll just have to do that yourself). If you ever want to dump real memory, you'll have to reset the offset to 0: O0 but then set it back. If you are not sure what it is, typing O will tell the current offset. Hoo, boy! Hope this kludge of documentation is enough to get you going - hmmm, better give you some of the gotcha's I've discovered... ---- WATCH FOR ---- * Symbols overflowing into the .COM. (Use ? command to see how full symbol table is) * Control entries overflowing into .SYM (altho I can't believe anyone will have a program with more than 512 control entries!!!) * Comments overflowing into BDOS (ug!!) * Using an offset which is not in free memory and overlaying BDOS or whatever. * The B(uild) command gobbling up too much when building a DB: "B" will take a DB 'GOBBELDY GOOK' followed by LXI H,FOO and take the LXI as a '!' (21H) so you'll have to manually stick a new "I" control entry in at the address of the LXI. You might also delete the incorrect "I" entry which RESOURCE stuck in (typically at the second byte of the LXI) * Trying to dump real memory without setting the offset back to 0. (then forgetting to set it back to its proper value) * Forgetting how big the .COM file you are disassembling was. * Using RESOURCE to rip off software (yes, I know, you heard that before, but only 3 in 100 needed to be told, and 2 in 100 needs to be told again, and 1 in 100 doesn't give a rat's fuzzy behind anyway!!) * Forgetting to take checkpoints when disassembling large files. You may even want to rotate the names under which things are saved: STEMP1.SYM STEMP1.CTL STEMP1.DOC * Missing a label: Suppose you have a control entry for a DW, resulting in: DFLT: ;172C DW 100H but somewhere in the program, the following exists: LDA 172DH Even if you did a B and have a label L172D, it won't show up since it's in the middle of a DW. Instead, do this: K.l172d kill the old label e172d,.dflt+1 put in the new label as a displacement off the beginning. * improperly disassembling DW's (see previous item). You might be tempted to make DFLT a DB so that DFLT: ;172C DB 0 L172D: ;172D DB 1 Note that while this disassembles and reassembles properly, it is not "as correct" as the technique used in the previous item. * Having the "B" command overlay your "E" control entry. What? Well, "B"uild is pretty dumb. If he finds 8 DB type characters in a row, he fires off a DB from then on until he runs out of those characters. Suppose your program was 200 long (ended at 3FF), and you had zeroed (aha! Nice DB candidates) memory there (there meaning at your offset address + whatever). Then you QB100,400 and viola!! RESOURCE overlaid your "E" control with a "B". ---------------- RESOURCE is relatively complete. (well, actually, the phrase "rampant featureitis" has been "mentioned"). ...But there's always another day, and another K... SO... Here's my "wish list" ..it might save you telling me YOU think such-and-such would be nice... * Targets of LHLD, SHLD should automatically be flagged as type DW in the control table. Ditto LDA and STA as DB or as second half of DW. Ditto targets of LXI as DB (?). * E5C,.FCB followed by E6C,.FCB+ should automatically calculate the appropriate displacement, and put it in the symbol table. * The comments facility should be enhanced to allow total SUBSTITUTION of entire line(s) of the code, i.e. at address such-and-such, replace the next 3 bytes with the following arbitrary line. This would help those "how do I explain what was being done" cases such as: LXI H,BUFFER AND 0FF00H * Add the ability to, in one instruction, rename a default (LXXXX) label to a meaningful name. ---------------- RESOURCE types an "*" prompt when it is loaded. You may then enter any of the following commands. Each command is a single letter followed by operands. Commas are shown as the delimiter, but a space will also work. ---------------- ---------------- ; Put comments into the program. (must execute 'u' command first, to assign area for comments to be placed) ;addr,comment enter a comment ;addr lists existing comment ; lists entire comments table ;addr, deletes existing comment note that '\' is treated as a new line, i.e. \test\ will be formatted: ; ;TEST ; ---------------- Attempt to find DB's while listing the program. - This command works just like 'L', but attempts to find DB's of 8 chars or longer. (see 'L' command for operand formats) ---------------- Build default sym tbl (LXXXX) labels for each - 2 byte operand encountered. Note 'B' is identical to 'L' except labels are built. (see 'L' command for operand formats) ---------------- Control table usage: - c dump ctl tbl cnnnn dump from starting cnnnn,x define format from nnnn to next entry. values of x: B = DB (attempts ASCII printable, 0DH, 0AH, 0) W = DW (attempts label) S = DW to next ctl entry I = instructions K = kill this ctl entry E = end of disassembly NOTE every control entry causes a "control break" (NO, RESOURCE was NOT written in RPG) which means a new line will be started. Thus if you have a string in memory which disassembles as: DB 'Invalid operand',0DH DB 0AH You might want to change it putting the 0DH,0AH together on the second line - just enter a "B" control entry for the address of the 0DH. The same technique could be used to make DB 'TYPESAVEDIR ERA REN ' appear as DB 'TYPE' DB 'SAVE' DB 'DIR ' DB 'ERA ' DB 'REN ' ---------------- dump: - dxxxx Dumps 80H from xxxx on daaaa,bbbb Dumps from aaaa thru bbbb d,bbbb Continues, thru bbbb d Continues, 80H more NOTE 80H is the default dump length. If you have a larger display, you can change the default via: d=nn nn is the HEX new default. For example, a 24 line tube could display 100H: d=100 or.. d=100,200 Defaults to 100, dumps 200-2ff ---------------- enter symbol: - ennnn,.symbol symbol may be of any length, and contain any char A-Z or 0-9, or "+" or "-". This allows: E5D,.FCB+1. Note the "+" is not checked, i.e. E5D,.FCB+2 would be wrong (assuming FCB is at 5C) but would be allowed to be entered. Note if you enter two symbols for the same address, whichever one is first alphabetically will show up on the disassembled listing. If you have a label which has the wrong address, you need not explicitly kill the old one before entering the new. A label which is spelled exactly the same as an existing one will replace the existing one even if the addresses are different. ---------------- Find occurrence of address or label. Note this function - runs until interrupted (press any key). fnnnn,ssss find address nnnn in memory. Start the search at ssss. Runs forever. Press any key to stop. f continue previous find command fnnnn find nnnn starting at address you last stopped at in the f command ---------------- kill symbol from table - k.symbol ---------------- list (disassemble). This command is used to list the - file, or to list it to disk after enabling the .ASM file save via 'SFILENAME.ASM' command l lists 10 lines from prev pc lssss,eeee lists from ssss to eeee l,eeee lists from current pc to eeee lssss lists 10 lines at ssss Note that if you have a control 'e' entry, then the list will stop when that address is found. This allows you to 'lstart,ffff'. The 10 line default may be changed via: L=nn where nn is a HEX line count, e.g. L=14 set to 20 lines/screen You can change the default and list, e.g. L=9,100 Dflt to 9 lines, list at 100. NOTE when using L to list the .ASM program to disk, you should either list the entire program at once using: Lssss,eeee or, you can list small pieces at a time. As long as you list again without specifying a starting address, (L or L,nnnn) then the output file will continue uninterrupted. You may do dump commands, and others, without affecting what is being written to disk. ---------------- offset for disassembly - o print current offset onnnn establish new offset (note the offset is always added to any address specified in an a, b, d, or l command. to dump real memory, the offset must be reset to 0 (O0) before the dump.) ---------------- prolog generation - this routine generates an - ORG instruction, and equates for any label outside of a given low-hi address pair. (the start and end addresses of your program). e.g. if disassembling from 100 to 3ff, it will generate 'fcb equ 5ch' if FCB is in the symbol table. In typical use, you would 'sfilename.asm' then use the P command to write the prolog, then the L command to write the program itself. Pstart addr,end addr quiet command: any command which is preceeded by a q - will be done 'quietly'. For example, to save a .asm program, you could just do: ql100,3ff or ql100,ffff if you have set the 'e' control in the control table. Another use is to build a default symbol table by taking a pass thru the program: QB100,xxxx ---------------- read .com, .ctl, .sym, or .doc file - rfilename.com reads in at offset+100h rfilename.ctl loads the ctl table rfilename.sym loads the sym file rfilename.doc loads the comments table (note 'u' command must have been issued) ---------------- save .asm, .ctl, .sym, or .doc file - sfilename.asm use 'l' command to write, z to end sfilename.CTL saves the CTL table stablename.sym saves the sym file sfilename.doc saves the comments table ---------------- use area of memory for comments table - unnnn such as ud000 if you had an open board at 0d000h ---------------- purge sym tbl and CTL tbl x - ---------------- close .asm file (note that a preferred way to close the .asm file is to have specified a control entry for the end address (e.g. c1ff,e)) z - -------------------------------------------- -------------------------------------------- Here is a sample of the RESOURCE usage. Given: a COM file (lets say test.com) which runs at 100 (as any good COM file should), and goes thru 2FF. lines preceeded with ---> are typed by you. ---> RESOURCE ---> o2200 set the offset to 2200, which means the program will read into 2200 + 100 = 2300. ---> rtest.com reads the com file into memory. system says: 2500 0300 which is the actual hi load addr, (2500) and the original hi load addr (300) REMEMBER this address (300) because you might want to put a "E" (end of assembly) control entry there. <<<<note>>>> that all 'L' (disassembly list) and 'D' (dump) commands work with the offset added. Thus, you should learn to forget that the disassembler is in memory, and think of it as if your program were actually at 100. D100 will dump your program. also note: if the program being "RESOURCEd" will have a fairly large symbol table, then you will have to set the offset higher: o2f00 or some such. (the ? command will show symbol table usage: if your symbol table is nearing the .com file, then just set a new offset (higher) and re-load the .com) if you want to dump r-e-a-l memory, you would have to reset the offset to 0: o0 (but don't forget to reset it to 1f00 before continuing with your program.) If you are disassembling something which is in memory at it's correct address (such as looking at ccp) then don't set the offset. It defaults to 0 when dis is first loaded. ---> l100 list your program - lists "about" 10 lines. ---> d100 do a dump of your program. NOTE that typically here are the steps to disassembling a program which has just been read into memory: Use the dump command to find the ASCII DB areas. Note that the 'a' command may be used to automatically find the db's, but you must then check them to insure that they don't extend too far. All printable characters, 0dh, 0ah, and 00h are considered candidates for ascii db's. At least 8 characters in a row must be found to make sure that long sequences of mov instructions won't be taken as db's. Use the cnnnn,k command to kill erronious entries put in the control table by the a command, but then immediately put in the right address, such as via cnnnn,i if you wanted to scan the program for ascii db's yourself, use the 'c' (control) command to set the beginning and end of ascii areas. For example, a program which starts out: 0100 jmp start 0103 db 'copyright .....' 0117 start ..... would show up in the dump as: 0100 c3170144 4f50xxxx xxxxxxxx xxxxxxxx *...copyr ight....* 0110 xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx *xxxxxxxx ........* thus you would want to instruct the disassembler to switch to db mode at 103, and back to instruction mode at 117, thus: c103,b c117,i Continue doing this, bracketing every ascii db which is in the middle of instructions, by a b control instruction and an i control instruction. Note that multiple db's in a row need not have separate cnnnn,b instructions, but that these do cause a 'line break', i.e. if you have a table of ascii commands, for example: 02e5 db 'load' 02e9 db 'save' the disassembler would disassemble these as: 02e4 db 'loadsave' you could put in an additional control entry: c2e9,b, which would cause the disassembler to generate: 02e4 db 'load' 02e8 db 'save' which is much more readable and realistic. Note that before generating each byte of a db, a symbol table lookup is done to determine if there is a label at that location, and if so, a new line is started. Thus if 'loadlit' and 'savelit' were in the symbol table, as the labels on the 'load' and 'save' above, no separate 'b' control instruction would be required as the label would cause the break. <<<<NOTE>>>> that at this time the automatic label checking is n-o-t done for ds instructions. Make sure that each ds instrucion references only up to the next label. This means that multiple ds's in a row must each be explicitly entered into the control table. Presence of a label is not sufficient. ---- steps, continued: After building the control entries with cnnnn,b and cnnnn,i put in a control entry cnnnn,e which defines the address of the end of your program. The l command will then automatically stop there, and in addition, if you are in 'save xxx.asm' mode, the output .asm file will be closed. If you do mot define a control 'e' entry, then you will have to use the break facility to stop the l command (don't use control-c as that will re-boot cp/m). If you were writing an .asm file, you would have to user the z command to close the file. Next, you would list your program to determine how it looks. when you recognize a routine by it's function, insert a label. For example, if you saw that location 7ef was a character out routine (type) then enter a label into the symbol table: E7EF,.TYPE NOTE that all symbols start with a '.', so as to be dis- tinguished from hex data. NOTE that if you want the disassembler to make default labels for you, use b (for build labels) instead of l (for list program). The b commands causes lnnnn default labels to be inserted in the symbol table for every 2 byte operand encountered (LXI, SHLD, JMP, etc). It will undoubtedly make some you don't want, such as L0000. You will have to: K.L0000 kill label L0000 from the table. When you encounter data reference instructions, try to determine what type of area the instruction points to. Typically,, LXI instructions may point to a work area which should be defined as a DS, or to an ASCII string, in which case we will have already made it a 'b' control instruction. Operands of LHLD and SHLD instructions should be made DW instructions. For example if you encounter LHLD 0534H, then issue a control instruction: C534,W NOTE that whatever mode you are last in will remain in effect. Therefore if 534,w is the last entry in the control table, all data from there on will be taken to be DW's. Suppose that you determine that address 7cf is a 128 byte buffer for disk I/O. You want it to disassemble to: DKBUF ;07CF DS 80H You do this as follows: C7CF,S to start the DS C84F,B to define it's end, and E7CF,.DKBUF to put the symbol in the table. Continue, iteratively using the 'l' command and the 'c' and 'e' commands until you have the listing in a nice format. You will then probably want to save the control symbol, and comments tables. Or, you could have been saving them at checkpoint times (so if you make a major mistake you could go back to a previous one). To save a control file: sfilename.CTL (any filename, may include a: or b:) To save a symbol file: sfilename.sym To save a comments file: sfilename.doc (not ".com" of course) NOTE that the filetypes must be used as shown, but that any legal filename (or disk:filename such as b:xxxx.CTL) may be used. You could now control-c to return to CP/M, and come back later to resume your disassembly: RESOURCE o2200 rtemp.com rtemp.sym rtemp.ctl uxxxx (such as u4000) rtemp.doc This will take you back exactly where you left off. If you want to save a .asm file out to disk, do the following: Make sure that there is a control entry defining the end of the program (such as c200,e) or else you will have to specify the ending address and manually type a z command to close the file. sfilename.asm A message will indicate that the file is opened. Any subsequent a, b, or l command will have whatever is listed written to disk. Encountering a 'e' control, or typing a z command will then close the .asm file. The listing may be interrupted, and continued. Since the l command types only 10 lines, use laddr,ffff to list thru the end of the assembly. If this is the 'final' save of the .asm file, you will probably want to put an 'org' at the beginning of the output file, as well as generate equ instructions for any references outside of the program. For example, a typical cp/m program will have references to: bdos at 5 fcb at 5ch tbuff at 80h the 'p' (for prologue) command generates the org, then scans the symbol table and generates equates: BDOS EQU 05H FCB EQU 05CH (etc.) If you have a "e" control entry in your file, you can list as follows: laddr,ffff - the listing will continue until the "e" control entry is found additional commands: if you entered a label in the symbol table but now want to get rid of it: k.symbol note to rename a symbol, such as when you had a system- assigned lnnnn label but now want to make it meaningful: k.l0334 e334,.type you could even: e.l0334,.type k.l0334 but that takes more typing. here are some more commands: ? prints statistics on symbol and control table usage, etc. c prints the entire control table cnnnn prints the control table starting at address nnnn ds dumps the symbol table. Interrupt it by typing any key. ds.symbol starts dumping at the specified symbol, or the nearest symbol. thus "ds.f" starts the dump at the first label starting with the letter 'f'. ....have fun, and let me know of any problems or suggested improvements ------------------------ RESOURCE "Quick" command summary Any address may be replaced by .symbol i.e. D.START ;addr,comment Enter a comment ;addr Lists existing comment ; Lists entire comments table ;addr, Deletes existing comment A(see "L" for operands) Attempt to find DB's B(see "L" for operands) Build default sym tbl (Lxxxx) C Dump ctl tbl Cnnnn Dump ctl starting at nnnn Cnnnn,x Define format from nnnn (B,E,I,S,W) Dxxxx Dumps 80H from xxxx on Daaaa,bbbb Dumps from aaaa thru bbbb D,bbbb Dump thru bbbb D Dump 80H more D=nn nn= Hex dump size default. Ds Dumps the symbol table. Ds.symbol Sym dump starting at .symbol Ennnn,.symbol Enter symbol into table Fnnnn,ssss Find address nnnn starting at ssss F Continue previous find command Fnnnn Find nnnn K.symbol Kill symbol from symbol table L Lists 10 lines from prev pc Lssss,eeee Lists from ssss to eeee L,eeee Lists from current pc to eeee Lssss Lists 10 lines at ssss L=nn nn is hex list default # of lines O Print current offset Onnnn Establish new offset Pstart addr,end addr Generate program prolog Q Before any command suppresses console output: QB100,200 Rfilename.COM Reads in at offset+100h Rfilename.CTL Loads the ctl table Rfilename.SYM Loads the sym file Rfilename.DOC Loads the comments table (note Sfilename.ASM Save .ASM file. Write w/L, Z to end Sfilename.CTL Saves the CTL table Sfilename.SYM Saves the sym file Sfilename.DOS Saves the comments table Unnnn Use nnnn for comments table X Purge all symbols and control Z Write eof to .ASM file ( ? Prints statistics (sym, ctl, comments)