Thanks for pointing out Opcode.

So here's my opcode hunter:

#!/usr/bin/perl -w

use strict;
use Opcode qw(opset opmask_add opset_to_ops invert_opset);

my $code = shift;
defined $code or 
    die "Usage: $0 <code> <permitted_opcode> <permitted_opcode> ...\n"
+;
# skip some masks from prev operations
my %skip;
$skip{$_}++ for @ARGV;

my @all = opset_to_ops(invert_opset(opset()));

# Try all opcodes, print error if eval failed
foreach ( @all ) {
    $skip{$_} and next;
    opmask_add(opset($_));
    eval $code and next;
    print "Eval failed on opcode: $_ with error: $@\n";
    exit 1;
};

print "Eval OK\n";
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For input "my $x; 1" it requires four operators - const padany lineseq leaveeval

padany is the one responsible for the "private vatriable" error observable in this thread.

Now how come private variable is needed in "eval 1"? SIGDIE is my friend! Sooo... Let's get a stack trace:

#!/usr/bin/perl -w

use strict;
use warnings;
use 5.012;

use Safe;
use Carp;

my $code = shift;
die "Usage: $0 <code> <premitted op> <permitted op> ..." unless define
+d $code;

my @perm = @ARGV;

print "Trying: $code\n";

my $compartment = Safe->new;
$compartment->share('*STDIN');
$compartment->share('&Dumper');

$compartment->permit_only(@perm);

# Trap detailed stack trace
my $stack;
local $SIG{__DIE__} = sub { $stack = Carp::longmess(shift) };
print $compartment->reval($code);

if ($@) {
    print "Unsafe code detected: $@";
    print "At: $stack";
}
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Here's my stack trace (note Carp complaining).

bash$ perl safe2.pl 1 
Trying: 1
Unsafe code detected: 'private value' trapped by operation mask at (ev
+al 5) line 1.
At: 'private value' trapped by operation mask at (eval 5) line 1.
 at (eval 5) line 1
    eval 'my $__ExPr__;1
;' called at (eval 4) line 1
    main::__ANON__(** Incomplete caller override detected; @DB::args w
+ere not set **) called at /usr/share/perl/5.14/Safe.pm line 358
    eval {...} called at /usr/share/perl/5.14/Safe.pm line 358
    Safe::reval(** Incomplete caller override detected; @DB::args were
+ not set **) called at safe2.pl line 26
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Aha, so Safe has added a "my" to my code before executing it. Finally, let's enable opcodes found by first script:

bash$ perl safe2.pl 1 padany const leaveeval lineseq
Trying: 1
1
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