greim@sbsvax.UUCP (Michael Greim) (03/24/88)
Hi folks, With the utmost humidity and hoping not to be a nuance I herewith adventure to percent a new fix for an old bug of csh. Symptoms: There is an 4bsd undocumented feature of history mechanism in csh. With !# you can get the whole last command. When you try alias a '\!#' b;a the csh will take a loooooooong time. Quite probably it will dump core. It is not neccessary for b to have any special value or even to exist. Diagnosis: When doing the alias substitution a new command line is built substituting the old command line in place of 'a'. Then this line is searched for candidates for alias substitution. The new 'a' at the end of the new line is found, and alias substitution happens. Old 'a's are marked, so 'a;b' does not produce garbage. In our example the line grows with each alias substitution: b;a b;b;a b;b;b;b;b;a ... In short, let l0 = 4 (end-of-wordlist counts !), then ln = 2^n * (l0-2) + 2 is the number of words in the input list after n substitutions. csh does only 20 alias substitutions (or is it 21 ?), but after that time the number of words is 2.097.154. And it takes a long time to reach this result. Therapy: Firstly, add a line to sh.local.h defining MAX_PARAMS, the maximal number of words in the input while alias substituting. Example: #define MAX_PARAMS 2000 2000 is a value I seem to find quite sufficient. Secondly, apply the following context diff. *** sh.parse.c.old Thu Mar 24 13:55:12 1988 --- sh.parse.c Thu Mar 24 13:55:11 1988 *************** *** 34,43 **** --- 34,67 ---- resexit(osetexit); } + static int + too_long (p1, p2) + register struct wordent *p1, *p2; + /* + * 15.jan.88 mg + * it was possible to get csh into an endless loop. + * Just type : alias a '\!#' then b; a + * Diagnosis : the alias routine substitute the command to "b;!#" + * then lex is called, which substitutes "b;b;a". The alias routines + * continue to run on the wordlist, but it gets longer each time, so + * an end is only reached when the list is 2**21 + 2 entries long, and + * this take long and needs a lot of memory. + * This routines here counts the number of words in the list. + * Maximum number of 2000 should be sufficient. + */ + { + register int i; + + for (i=0; p1!=p2 && i<MAX_PARAMS; i++, p1=p1->next); + return (i<MAX_PARAMS ? 0 : 1); + } + asyntax(p1, p2) register struct wordent *p1, *p2; { + if (too_long(p1,p2)) + error ("Infinite alias substitution loop detected"); while (p1 != p2) if (any(p1->word[0], ";&\n")) p1 = p1->next; Absorb, apply and enjoy, Michael -- +------------------------------------------------------------------------------+ | UUCP: ...!uunet!unido!sbsvax!greim | Michael T. Greim | | or greim@sbsvax.UUCP | Universitaet des Saarlandes | | CSNET: greim%sbsvax.uucp@Germany.CSnet| FB 10 - Informatik (Dept. of CS) | | ARPA: greim%sbsvax.uucp@uunet.UU.NET | Bau 36, Im Stadtwald 15 | | Phone: +49 681 302 2434 | D-6600 Saarbruecken 11, West Germany | +------------------------------------------------------------------------------+ | Watch this space. Don't let it escape. | +------------------------------------------------------------------------------+
daniel@unicom.UUCP (Dan Smith, not your average Lithuanian...) (03/29/88)
In article <470@sbsvax.UUCP> greim@sbsvax.UUCP (Michael Greim) writes: >Symptoms: > > There is an 4bsd undocumented feature of history mechanism in csh. > With !# you can get the whole last command. > When you try > alias a '\!#' > b;a > the csh will take a loooooooong time. Quite probably it will dump > core. It is not neccessary for b to have any special value or > even to exist. > whoa! quick comment time... I'm running 4.3 BSD on a Vax 11/750, and Sun 4.2 R3.5 on various Suns. The use of "!#" is "the command line typed in so far..." very useful for things like renaming files via: mv longfilename.c really!#:1 which gives you "reallylongfilename.c". I've never had to use things like "!#:2-4", but that's possible, as well as: "echo this is !#:1:s/is/at" For more clarification (This is *not* "the last command", at least on the versions I mentioned...), see "The C Shell Field Guide" by Gail & Paul Anderson. I hope this averts some confusion among csh users reading this :-) dan dan smith, island graphics, marin co, ca|"A womp ba ba lu ba, a womp bam boom!" uucp: {ucbvax!ucbcad,sun}!island!daniel | ph: +1 (415) 491 1000 (W), 332 FAST, uucp: pixar!unicom!daniel, well!daniels | 332 EASY (H)| unix/guitars/films/tuna