$ cat 794362.pl
#!/usr/bin/perl

use strict;
use warnings;

print "Hello world!\n";


$ PERLDB_OPTS="AutoTrace NonStop frame=2"  perl -d 794362.pl
entering CODE(0x65f740)
 3:     use strict;
 3:     use strict;
 3:     use strict;
 entering strict::import
  28:       shift;
  29:       $^H |= @_ ? bits(@_) : $default_bits;
 exited strict::import
exited CODE(0x65f740)
entering CODE(0x65f780)
 4:     use warnings;
 4:     use warnings;
 4:     use warnings;
 entering warnings::import
  336:      shift;
  338:      my $catmask ;
  339:      my $fatal = 0 ;
  340:      my $no_fatal = 0 ;
  342:      my $mask = ${^WARNING_BITS} ;
  344:      if (vec($mask, $Offsets{'all'}, 1)) {
  349:      push @_, 'all' unless @_;
  351:      foreach my $word ( @_ ) {
  352:          if ($word eq 'FATAL') {
  361:              $mask |= $catmask ;
  362:              $mask |= $DeadBits{$word} if $fatal ;
  363:              $mask &= ~($DeadBits{$word}|$All) if $no_fatal ;
  369:      ${^WARNING_BITS} = $mask ;
 exited warnings::import
exited CODE(0x65f780)
Package 794362.pl.
6:      print "Hello world!\n";
Hello world!