Re: [9fans] Undefined Behaviour in C

[Ryan Gonzalez <rymg19@gmail.com>]

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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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