p5pRT
commented
22 years ago From vallon@bear.com
Created by vallon@bear.com
(Also reproduced in 5.005)
SAMPLE CODE: Here is a sample program:
local @X;
local @Y;
sub F {
print join('\,'\, @_)\, "\n";
@X = ();
print join('\,'\, @_)\, "\n";
@Y = qw/ magic /;
print join('\,'\, @_)\, "\n";
}
@X = qw/ A B C D E /;
F('start'\, @X\, 'end');
With the curious output:
start\,A\,B\,C\,D\,E\,end start\,\,\,\,\,\,end start\,magic\,\,\,\,\,end
BUG: The bug is that in F\, after @X is emptied\, @_ seems to contain dangling references. The allocation of 'magic' seems to reuse some recently released memory\, and @_ (still) references that memory.
EXPECTED BEHAVIOR: How is this supposed to work? What should @_ reference if @X gets shorter? My guess would be that it evaluates to undef for @_ elements that reference truncated values of @X\, and assignment to non-existent values automatically extends @X (ala lvalue array entries).
BIGGER EXAMPLE: In the following\, @_ ends up referencing something that causes a croak from within Perl_sv_setsv ("Bizarre copy of..."). As with all memory corruption\, actual behavior is undefined.
#!/usr/local/bin/perl5.6.1 -w
local @X;
sub Main { print 'orig: '\, join('\,'\, @_)\, "\n"; # 'start'\, 'A'..'M'\, 'end'
@X = ();
print 'clear: '\, join('\,'\, @_)\, "\n"; # @_ seems ok\, but isn't
my @z = qw/ MAGIC STRINGS /;
print 'magic: '\, join('\,'\, @_)\, "\n"; # oops\, dangling pointer???
require Carp; # massage heap
print 'trash: '\, join('\,'\, @_)\, "\n"; # oops\, more trash from load
my @a = @_; # crash (maybe?) : Bizarre copy of CODE in aassign at ./test2 line 9. }
@X = qw/ A B C D E F G H I J K L M /; Main('start'\, @X\, 'end');
Migrated from rt.perl.org#8358 (status was 'open')
Searchable as RT8358$