Re: [9fans] Undefined Behaviour in C

[Brantley Coile <brantleycoile@me.com>]

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Bruce's law: undefined != stupid

Sent from my iPad

> On Nov 25, 2015, at 9:04 PM, Prof Brucee <prof.brucee@gmail.com> wrote:
> 
> gcc is indeed a very sad tome. The mmap of 0 is disgusting. I like kenc. It just works. My behaviour this afternoon will be undefined but not as stupid as that of some programmers.
> 
>> On 26/11/2015 5:43 AM, "Brantley Coile" <brantleycoile@me.com> wrote:
>> Align it to column 7 and it looks like all the code I saw when I started. 
>> 
>> iPhone email
>> 
>>> On Nov 25, 2015, at 12:13 PM, Ryan Gonzalez <rymg19@gmail.com> wrote:
>>> 
>>> Neither! It's what happens when you run sed 's/^\s*//' on your whole code base, yielding results like (from cmd/yacc.c):
>>> 
>>> 
>>> void
>>> setup(int argc, char *argv[])
>>> {
>>> long c, t;
>>> int i, j, fd, lev, ty, ytab, *p;
>>> int vflag, dflag, stem;
>>> char actnm[8], *stemc, *s, dirbuf[128];
>>> Biobuf *fout;
>>> 
>>> ytab = 0;
>>> vflag = 0;
>>> dflag = 0;
>>> stem = 0;
>>> stemc = "y";
>>> foutput = 0;
>>> fdefine = 0;
>>> fdebug = 0;
>>> ARGBEGIN{
>>> case 'v':
>>> case 'V':
>>> vflag++;
>>> break;
>>> case 'D':
>>> yydebug = ARGF();
>>> break;
>>> case 'a':
>>> yyarg = 1;
>>> break;
>>> case 'd':
>>> dflag++;
>>> break;
>>> case 'l':
>>> yyline = 0;
>>> break;
>>> case 'o':
>>> ytab++;
>>> ytabc = ARGF();
>>> break;
>>> case 's':
>>> stem++;
>>> stemc = ARGF();
>>> break;
>>> case 'S':
>>> parser = PARSERS;
>>> break;
>>> default:
>>> error("illegal option: %c", ARGC());
>>> }ARGEND
>>> openup(stemc, dflag, vflag, ytab, ytabc);
>>> fout = dflag?fdefine:ftable;
>>> if(yyarg){
>>> Bprint(ftable, "#define\tYYARG\t1\n\n");
>>> }
>>> if((fd = mkstemp(ttempname)) >= 0){
>>> tempname = ttempname;
>>> ftemp = Bfdopen(fd, OWRITE);
>>> }
>>> if((fd = mkstemp(tactname)) >= 0){
>>> actname = tactname;
>>> faction = Bfdopen(fd, OWRITE);
>>> }
>>> if(ftemp == 0 || faction == 0)
>>> error("cannot open temp file");
>>> if(argc < 1)
>>> error("no input file");
>>> infile = argv[0];
>>> if(infile[0] != '/' && getwd(dirbuf, sizeof dirbuf)!=nil){
>>> i = strlen(infile)+1+strlen(dirbuf)+1+10;
>>> s = malloc(i);
>>> if(s != nil){
>>> snprint(s, i, "%s/%s", dirbuf, infile);
>>> cleanname(s);
>>> infile = s;
>>> }
>>> }
>>> finput = Bopen(infile, OREAD);
>>> if(finput == 0)
>>> error("cannot open '%s'", argv[0]);
>>> cnamp = cnames;
>>> 
>>> defin(0, "$end");
>>> extval = PRIVATE;	/* tokens start in unicode 'private use' */
>>> defin(0, "error");
>>> defin(1, "$accept");
>>> defin(0, "$unk");
>>> mem = mem0;
>>> i = 0;
>>> 
>>> for(t = gettok(); t != MARK && t != ENDFILE;)
>>> switch(t) {
>>> case ';':
>>> t = gettok();
>>> break;
>>> 
>>> case START:
>>> if(gettok() != IDENTIFIER)
>>> error("bad %%start construction");
>>> start = chfind(1, tokname);
>>> t = gettok();
>>> continue;
>>> 
>>> case TYPEDEF:
>>> if(gettok() != TYPENAME)
>>> error("bad syntax in %%type");
>>> ty = numbval;
>>> for(;;) {
>>> t = gettok();
>>> switch(t) {
>>> case IDENTIFIER:
>>> if((t=chfind(1, tokname)) < NTBASE) {
>>> j = TYPE(toklev[t]);
>>> if(j != 0 && j != ty)
>>> error("type redeclaration of token %s",
>>> tokset[t].name);
>>> else
>>> SETTYPE(toklev[t], ty);
>>> } else {
>>> j = nontrst[t-NTBASE].value;
>>> if(j != 0 && j != ty)
>>> error("type redeclaration of nonterminal %s",
>>> nontrst[t-NTBASE].name );
>>> else
>>> nontrst[t-NTBASE].value = ty;
>>> }
>>> case ',':
>>> continue;
>>> case ';':
>>> t = gettok();
>>> default:
>>> break;
>>> }
>>> break;
>>> }
>>> continue;
>>> 
>>> case UNION:
>>> /* copy the union declaration to the output */
>>> cpyunion();
>>> t = gettok();
>>> continue;
>>> 
>>> case LEFT:
>>> case BINARY:
>>> case RIGHT:
>>> i++;
>>> 
>>> case TERM:
>>> /* nonzero means new prec. and assoc. */
>>> lev = t-TERM;
>>> ty = 0;
>>> 
>>> /* get identifiers so defined */
>>> t = gettok();
>>> 
>>> /* there is a type defined */
>>> if(t == TYPENAME) {
>>> ty = numbval;
>>> t = gettok();
>>> }
>>> for(;;) {
>>> switch(t) {
>>> case ',':
>>> t = gettok();
>>> continue;
>>> 
>>> case ';':
>>> break;
>>> 
>>> case IDENTIFIER:
>>> j = chfind(0, tokname);
>>> if(j >= NTBASE)
>>> error("%s defined earlier as nonterminal", tokname);
>>> if(lev) {
>>> if(ASSOC(toklev[j]))
>>> error("redeclaration of precedence of %s", tokname);
>>> SETASC(toklev[j], lev);
>>> SETPLEV(toklev[j], i);
>>> }
>>> if(ty) {
>>> if(TYPE(toklev[j]))
>>> error("redeclaration of type of %s", tokname);
>>> SETTYPE(toklev[j],ty);
>>> }
>>> t = gettok();
>>> if(t == NUMBER) {
>>> tokset[j].value = numbval;
>>> if(j < ndefout && j > 3)
>>> error("please define type number of %s earlier",
>>> tokset[j].name);
>>> t = gettok();
>>> }
>>> continue;
>>> }
>>> break;
>>> }
>>> continue;
>>> 
>>> case LCURLY:
>>> defout(0);
>>> cpycode();
>>> t = gettok();
>>> continue;
>>> 
>>> default:
>>> error("syntax error");
>>> }
>>> if(t == ENDFILE)
>>> error("unexpected EOF before %%");
>>> 
>>> /* t is MARK */
>>> if(!yyarg)
>>> Bprint(ftable, "extern	int	yyerrflag;\n");
>>> Bprint(ftable, "#ifndef	YYMAXDEPTH\n");
>>> Bprint(ftable, "#define	YYMAXDEPTH	150\n");
>>> Bprint(ftable, "#endif\n" );
>>> if(!ntypes) {
>>> Bprint(ftable, "#ifndef	YYSTYPE\n");
>>> Bprint(ftable, "#define	YYSTYPE	int\n");
>>> Bprint(ftable, "#endif\n");
>>> }
>>> if(!yyarg){
>>> Bprint(ftable, "YYSTYPE	yylval;\n");
>>> Bprint(ftable, "YYSTYPE	yyval;\n");
>>> }else{
>>> if(dflag)
>>> Bprint(ftable, "#include \"%s.%s\"\n\n", stemc, FILED);
>>> Bprint(fout, "struct Yyarg {\n");
>>> Bprint(fout, "\tint\tyynerrs;\n");
>>> Bprint(fout, "\tint\tyyerrflag;\n");
>>> Bprint(fout, "\tvoid*\targ;\n");
>>> Bprint(fout, "\tYYSTYPE\tyyval;\n");
>>> Bprint(fout, "\tYYSTYPE\tyylval;\n");
>>> Bprint(fout, "};\n\n");
>>> }
>>> prdptr[0] = mem;
>>> 
>>> /* added production */
>>> *mem++ = NTBASE;
>>> 
>>> /* if start is 0, we will overwrite with the lhs of the first rule */
>>> *mem++ = start;
>>> *mem++ = 1;
>>> *mem++ = 0;
>>> prdptr[1] = mem;
>>> while((t=gettok()) == LCURLY)
>>> cpycode();
>>> if(t != IDENTCOLON)
>>> error("bad syntax on first rule");
>>> 
>>> if(!start)
>>> prdptr[0][1] = chfind(1, tokname);
>>> 
>>> /* read rules */
>>> while(t != MARK && t != ENDFILE) {
>>> /* process a rule */
>>> rlines[nprod] = lineno;
>>> if(t == '|')
>>> *mem++ = *prdptr[nprod-1];
>>> else
>>> if(t == IDENTCOLON) {
>>> *mem = chfind(1, tokname);
>>> if(*mem < NTBASE)
>>> error("token illegal on LHS of grammar rule");
>>> mem++;
>>> } else
>>> error("illegal rule: missing semicolon or | ?");
>>> /* read rule body */
>>> t = gettok();
>>> 
>>> more_rule:
>>> while(t == IDENTIFIER) {
>>> *mem = chfind(1, tokname);
>>> if(*mem < NTBASE)
>>> levprd[nprod] = toklev[*mem];
>>> mem++;
>>> t = gettok();
>>> }
>>> if(t == PREC) {
>>> if(gettok() != IDENTIFIER)
>>> error("illegal %%prec syntax");
>>> j = chfind(2, tokname);
>>> if(j >= NTBASE)
>>> error("nonterminal %s illegal after %%prec",
>>> nontrst[j-NTBASE].name);
>>> levprd[nprod] = toklev[j];
>>> t = gettok();
>>> }
>>> if(t == '=') {
>>> levprd[nprod] |= ACTFLAG;
>>> Bprint(faction, "\ncase %d:", nprod);
>>> cpyact(mem-prdptr[nprod]-1);
>>> Bprint(faction, " break;");
>>> if((t=gettok()) == IDENTIFIER) {
>>> 
>>> /* action within rule... */
>>> sprint(actnm, "$$%d", nprod);
>>> 
>>> /* make it a nonterminal */
>>> j = chfind(1, actnm);
>>> 
>>> /*
>>> * the current rule will become rule number nprod+1
>>> * move the contents down, and make room for the null
>>> */
>>> for(p = mem; p >= prdptr[nprod]; --p)
>>> p[2] = *p;
>>> mem += 2;
>>> 
>>> /* enter null production for action */
>>> p = prdptr[nprod];
>>> *p++ = j;
>>> *p++ = -nprod;
>>> 
>>> /* update the production information */
>>> levprd[nprod+1] = levprd[nprod] & ~ACTFLAG;
>>> levprd[nprod] = ACTFLAG;
>>> if(++nprod >= NPROD)
>>> error("more than %d rules", NPROD);
>>> prdptr[nprod] = p;
>>> 
>>> /* make the action appear in the original rule */
>>> *mem++ = j;
>>> 
>>> /* get some more of the rule */
>>> goto more_rule;
>>> }
>>> }
>>> 
>>> while(t == ';')
>>> t = gettok();
>>> *mem++ = -nprod;
>>> 
>>> /* check that default action is reasonable */
>>> if(ntypes && !(levprd[nprod]&ACTFLAG) && nontrst[*prdptr[nprod]-NTBASE].value) {
>>> 
>>> /* no explicit action, LHS has value */
>>> int tempty;
>>> 
>>> tempty = prdptr[nprod][1];
>>> if(tempty < 0)
>>> error("must return a value, since LHS has a type");
>>> else
>>> if(tempty >= NTBASE)
>>> tempty = nontrst[tempty-NTBASE].value;
>>> else
>>> tempty = TYPE(toklev[tempty]);
>>> if(tempty != nontrst[*prdptr[nprod]-NTBASE].value)
>>> error("default action causes potential type clash");
>>> }
>>> nprod++;
>>> if(nprod >= NPROD)
>>> error("more than %d rules", NPROD);
>>> prdptr[nprod] = mem;
>>> levprd[nprod] = 0;
>>> }
>>> 
>>> /* end of all rules */
>>> defout(1);
>>> 
>>> finact();
>>> if(t == MARK) {
>>> Bprint(ftable, "\n");
>>> if(yyline)
>>> Bprint(ftable, "#line\t%d\t\"%s\"\n", lineno, infile);
>>> while((c=Bgetrune(finput)) != Beof)
>>> Bputrune(ftable, c);
>>> }
>>> Bterm(finput);
>>> }
>>> 
>>> 
>>>> On Wed, Nov 25, 2015 at 10:03 AM, <plannine@sigint.cs.purdue.edu> wrote:
>>>> On Wed, Nov 25, 2015 at 09:25:55AM -0500, Brantley Coile wrote:
>>>> > unindented consequences
>>>> 
>>>> Is that a class of Python bugs or an awesome name for a Nerdcore band?
>>> 
>>> 
>>> 
>>> -- 
>>> Ryan
>>> [ERROR]: Your autotools build scripts are 200 lines longer than your program. Something’s wrong.
>>> http://kirbyfan64.github.io/

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