" -*-fundamental-*- " sh -- a shell " started by p budne 3/4/2016 " with code from cat.s, init.s, and looking at the v1 (pdp-11) shell start: " XXX take command line argument (script file to open), suppress prompt?? " NOTE!!! v0 init.s doesn't set up the argv at the top of memory, " so the v0 shell may not have taken command line arguments!!! " if non-interactive, "dzm prompt", jump to newcom interactive: -1 sys intrp " make shell uninterruptable sys getuid sma " <0? jmp newline " no, a mundane lac hash " yes: superuser dac prompt " change prompt newline: lac d1; sys write; prompt; 1 " output prompt newcom: dzm argc " clear arg count dzm char " clear saved char dzm infile " clear input redirect file name dzm outfile " clear output redirect file name dzm argv0 " clear out argv0 for chdir comparison dzm argv0+1 dzm argv0+2 lac iopt " reset output pointer dac opt dac nextarg newarg: -8 " save 8 chars dac bcount dzm redirect lac opt " save start for print (TEMP) dac 8f dac nextarg jms blank " skip whitespace sad o12 " newline? jmp eol " yes sad lt " input redirect? jmp redirin sad gt " output redirect? jmp redirout jmp 3f redirin: " saw < dac redirect " flag redirect lac infilep dac opt dac 8f " TEMP jmp newchar " v1 behavior? no whitespace eater redirout: " saw > dac redirect " flag redirect lac outfilep dac opt dac 8f " TEMP " v1 behavior? no whitespace eater " fall newchar: jms getc sad o40 " space? jmp ws " yes sad o12 jmp ws 3: jms putc " save isz bcount " loop unless full jmp newchar " here after 8 chars: discard until terminator seen discard: jms getc dac char sad o4 jmp eof sad o12 jmp eoname sad o40 jmp eoname jmp discard " here with EOF in command eof: sys exit " quit, for now? " name ended (short) with whitespace or newline " pad out last name to 8 with spaces ws: dac char 1: lac o40 jms putc " no: copy into argv isz bcount " loop until full jmp 1b " saw end of name eoname: lac redirect sza jmp 1f " last name was a redirect file, skip increment isz argc " increment argc lac nextarg tad d4 " advance nextarg dac nextarg 1f: dzm redirect " clear redirect flag " TEMP output each name on a line: lac d1; sys write; gt; 1 lac d1; sys write; 8:0; 4 lac d1; sys write; nl; 1 lac nextarg dac opt dac 8b " TEMP lac char sad o12 jmp eol -maxargs tad argc sza jmp newarg " too many args, (complain?) eat rest of line 4: jms getc sad o12 skp jmp 4b " here at end of line eol: cla " get anything? sad argc jmp newline " no, go back for another lac argv0 " check for built-in "chdir" command sad chdir skp jmp forkexec lac argv0+1 sad chdir+1 skp jmp forkexec lac argv0+2 sad chdir+2 jmp changedir forkexec: " temp just exec in place " sys fork " jmp parent dac pid " here in child: save parent pid for smes lac d2; sys close " close fd 2 " XXX open executable BEFORE I/O redirection, so we can output error!!!! sys unlink; exectemp " try to link binary from "system" directory to "exectemp" file " sys link; system; argv0; exectemp " spa " jmp notsys " sys open; exectemp; 0 " spa " jmp error " sys unlink; exectemp " jmp 1f lac d1; sys write; star; 1 lac d1; sys write; star; 1 lac d1; sys write; argv0; 4 lac d1; sys write; nl; 1 notsys: " not found in "system" sys open; argv0; 0 " try cwd spa jmp cmderr cla " check for input redirection sad infile jmp 1f sys close " close fd 0 sys open; infile; 0 " open redirected spa sna jmp inerror cla 1: sad outfile jmp exec lac d1; sys close " close fd 1 lac o17 sys creat; outfile " open output redirect spa jmp outerror " here to "exec" file open on fd 2, adapted from init.s: exec: law boot-1 " Get source addr dac 8 " set up index 8 (pre-increments) law bootloc-1 " Copy the code at the boot label into high memory dac 9 " set up index 9 (pre-increments) 1: lac 8 i dac 9 i isz bootcount jmp 1b jmp bootloc " and then jump to the code " copied up to bootloc in high memory (below argc) boot: lac d2 " Load fd 2 (the opened executable) lmq " Save the fd into MQ sys read; userbase; userlen " read executable in lacq " Get the fd back and close the file sys close jmp userbase " and jump to the beginning of the executable bootlen=.-boot " length of bootstrap bootcount: -bootlen " isz loop count for bootstrap copy " error in child process: inerror: " error opening input redirection lac infilep jmp error outerror: " error opening output redirection (stdout closed!) lac outfilep skp cmderr: " error opening command lac argv0p error: " here for error in child: filename pointer in AC dac 1f " save filename to complain about lac d1; sys write; qmsp; 1 lac d1; sys write; 1: 0; 4 lac d1; sys write; nl; 1 " XXX smes to parent??? lac d2; sys close sys exit " end code from init.s " ================ parent: dac pid 1: sys rmes sad pid jmp newline jmp 1b " chdir command: changedir: " XXX check argc > 1!!! lac d1; sys write; gt; 1 lac d1; sys write; gt; 1 lac d1; sys write; gt; 1 lac d1; sys write; argv0+4; 4 " XXX loop for multiple components!!! jmp newline " ================ " subroutines blank: 0 1: jms getc sad o40 jmp 1b jmp blank i " give skip return if AC *NOT* a command delimiter delim: 0 sad o12 jmp delim i isz delim jmp delim i " **************************************************************** " from cat.s getc: 0 lac ipt " Load the pointer to the next word in the buffer sad eipt jmp 1f " We've reached the end of the buffer, so read more dac 2f " Save the pointer add o400000 " Flip the msb and save into ipt dac ipt ral " Move the msb into the link register lac 2f i " Load the word from the buffer szl " Skip if this is the second character in the word lrss 9 " It's the first char, shift down the top character and o177 " Keep the lowest 7 bits sna jmp getc+1 " Skip a NUL characters and read another one jmp getc i " Return the character from the subroutine 1: cla " Buffer is empty, read another 64 characters sys read; ibuf; 64 sna jmp 1f " No characters were read in tad iipt " Add the word count to the base of the buffer dac eipt " and store in the end buffer pointer lac iipt " Reset the ipt to the base of the buffer dac ipt jmp getc+1 " and loop back to get one character 1: lac o4 " No character, return with ctrl-D jmp getc i " return from subroutine putc: 0 and o177 " Keep the lowest 7 bits and save into 2f+1 dac 2f+1 lac opt " Save the pointer to the empty buffer dac 2f " position to 2f add o400000 " Flip the msb and save back into opt dac opt " This also has the effect of incrementing " the opt pointer every second addition! spa " If the bit was set, we already have one jmp 1f " character at 2f+1. If no previous character, lac 2f i " merge the old and new character together xor 2f+1 jmp 3f " and go to the "save it in buffer" code 1: lac 2f+1 " Move the character up into the top half alss 9 3: dac 2f i " Save the word into the buffer jmp putc i " No, so return (more room still in the buffer) 2: 0;0 " Current input and output word pointers ipt: 0 " Current input buffer base eipt: 0 " Pointer to end of data read in input buffer iipt: ibuf ibuf: .=.+64 " end from cat.s " **************************************************************** " literals d1: 1 d2: 2 o4:d4: 4 o12:nl: 012 " newline o17: 017 o40:sp: 040 " space o74:lt: 074 o76:gt: 076 o177: 0177 " ASCII mask o400000: 0400000 " Msb toggle bit hash: <#> " superuser prompt qmsp: " " question mark, space " (traditional DDT error label was "dt" " for "dink, tab") system: ;;; 040040 exectemp: ;; " temporary link for file being exec'ed chdir: ;; " " ################ variables prompt: <@> " v1 prompt pid: 0 " "other" pid char: 0 " white space char redirect: 0 " last file was a redirect (lt or gt) bcount: 0 " byte counter for current filename iopt:argv0p: argv0 " initial value for nextarg, opt nextarg: 0 " next slot in argv to fill opt: 0 " "output pointer" (may point to in/outfile) infilep: infile outfilep: outfile outfile: .=.+4 " buffer for output redirect file name infile: .=.+4 " buffer for input redirect file name " leave room for maxargs items of 4 words each maxargs=8 userbase=010000 " user starts at 4K argptr=017777 " last word points to argc + argv data argc=argptr-maxargs-maxargs-maxargs-maxargs-1 " argc followed by argv " arguments in 4 word blocks follow argc argv0=argc+1 " "bootstrap" (reads executable into userbase) JUST below argc bootloc=argc-bootlen " location of bootstrap userlen=bootloc-userbase " max executable