Mon Aug 17 15:12:38 2009: Request 48770 was acted upon.
Transaction: Correspondence added by sch...@argumentum.de
Queue: PAR
Subject: Re: [rt.cpan.org #48770] $0 is not working when PAR is used
Broken in: (no value)
Severity: (no value)
Owner: Nobody
Requestors: mianro...@hotmail.com
Status: new
Ticket <URL: http://rt.cpan.org/Ticket/Display.html?id=48770 >
2009/8/17 Miguel Angel Rojas Gómez via RT <bug-...@rt.cpan.org>:
> It seems that $0 var is not processed properly inside PAR binaries:
It is. Your notion of "properly" is wrong :)
>From the Perl source (perl.c):
/* Set PL_origalen be the sum of the contiguous argv[]
* elements plus the size of the env in case that it is
* contiguous with the argv[]. This is used in mg.c:Perl_magic_set()
* as the maximum modifiable length of $0. In the worst case
* the area we are able to modify is limited to the size of
* the original argv[0]. (See below for 'contiguous', though.)
Try the following script (essentially your example):
print "before \$0=$0\n";
$0 = "12345678901234567890";
print "after \$0=$0\n";
system qw(ps -f), $$;
OK, run it:
$ perl foo.pl
before $0=foo.pl
after $0=12345678901234567890
UID PID PPID C STIME TTY STAT TIME CMD
roderich 17517 28077 0 21:04 pts/3 S+ 0:00 12345678901234567890
But this only works because most environments are large enough so that
the new value of $0 will fit in to the combined contiguous arg+env space.
If we shrink the environment to nothing it doesn't work anymore:
$ env - perl foo.pl
before $0=foo.pl
after $0=12345678901234567890
UID PID PPID C STIME TTY STAT TIME CMD
roderich 17647 28077 0 21:06 pts/3 S+ 0:00 12345678901
The same happens in a packed executable because it already manipulates
$0 (and @ARGV and the environment) before it even gets to execute
your script. Afterwards the "combined contiguous"
space has shrunk to the size of $0 itself and that's what you observe.
Sorry, no cake.
Cheers, Roderich
