[ID 20000124.003] perl 5.063 error in open(.., "-|")

[ton@aucs-europe.net]

This is a bug report for perl from hostmaster@att-unisource.net,
generated with the help of perlbug 1.26 running under perl 5.00503.


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[Please enter your report here]
perl -we 'for (1..2) { defined($pid = open(FILE, "-|")) || die "Could not fork: $!"; if ($pid) { print STDERR "parent $$\n"; while (<FILE>) {}; close FILE; } else { print STDERR "child $$\n"; exec("ls"); };}'

will hang on the second fork.

This is bug was introduced by the changes in open to support 3 arg open.
Relevant code in Perl_do_open9 in doio.c:

bool
Perl_do_open9(pTHX_ GV *gv, register char *name, I32 len, int as_raw,
              int rawmode, int rawperm, PerlIO *supplied_fp, SV *svs,
              I32 num_svs)
{
...
        char *myname;
        char *type = name;
...
        myname = savepvn(name, len);
        SAVEFREEPV(myname);
        name = myname;
...
                type[--tlen] = '\0';
                while (tlen && isSPACE(type[tlen-1]))
                    type[--tlen] = '\0';


Notice how the arg 'name' is saved, but the modification
through 'type' changes the OLD version. This causes the given program 
to call open(FILE, "-|") the first time, and open(FILE, "-") the
second time.

This modification through type happens several times in open9, so
it will be possible to construct many other cases.

[Please do not change anything below this line]
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Follow-Ups from:

Gurusamy Sarathy <gsar@ActiveState.com>

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