| Subject: | minmax() one arg access below stack |
| Date: | Sun, 19 Jul 2009 23:10:29 +0200 |
| To: | bug-List-MoreUtils [...] rt.cpan.org |
| From: | Ansgar Burchardt <ansgar [...] 2008.43-1.org> |
Hi,
I'm forwarding this bug report from the Debian BTS [1].
Regards,
Ansgar
[1] http://bugs.debian.org/532534
| Subject: | liblist-moreutils-perl: minmax() one arg access below stack |
| Date: | Wed, 10 Jun 2009 07:26:25 +1000 |
| To: | submit [...] bugs.debian.org |
| From: | Kevin Ryde <user42 [...] zip.com.au> |
Package: liblist-moreutils-perl
Version: 0.22-1+b1
Severity: normal
Tags: patch
The program foo.pl below gets errors
Use of uninitialized value in subroutine entry at foo.pl line 5.
Use of uninitialized value $min in concatenation (.) or string at foo.pl line 6.
where I hoped minmax() would return 100 for both minimum and maximum
when called with one arg.
I think the xsub for minmax() when with just one arg, ie. items==1,
accesses an item below its args on the stack. In the code
if (items & 1) {
asv = ST(items-2);
the ST(items-2) is ST(-1). No doubt what's there depends on the calling
context or something. foo.pl seems to see an undef, in one of my
programs I struck "non-numeric" warnings for hitting an alphabetic
string.
Perhaps items==1 can shortcut to the end of the func like below. The
ref counting is right just duplicating an existing arg, is it?
I think EXTEND(SP,2) is certainly needed though, the code shouldn't
store ST(1) at the end unless either items>=2 or an EXTEND.
Incidentally, the corresponding code in the pure-perl implementation is
ok because of course there $_[-1] on a length-one @_ means $_[0].
-- System Information:
Debian Release: squeeze/sid
APT prefers unstable
APT policy: (500, 'unstable')
Architecture: i386 (i586)
Kernel: Linux 2.6.26-1-486
Locale: LANG=en_AU, LC_CTYPE=en_AU (charmap=ISO-8859-1)
Shell: /bin/sh linked to /bin/dash
Versions of packages liblist-moreutils-perl depends on:
ii libc6 2.9-13 GNU C Library: Shared libraries
ii perl 5.10.0-22 Larry Wall's Practical Extraction
ii perl-base [perlapi-5.10.0] 5.10.0-22 minimal Perl system
liblist-moreutils-perl recommends no packages.
liblist-moreutils-perl suggests no packages.
-- no debconf information
use strict;
use warnings;
use List::MoreUtils 'minmax';
my ($min, $max) = minmax(100);
print "$min $max\n";
--- MoreUtils.xs.orig 2009-06-08 15:25:26.000000000 +1000
+++ MoreUtils.xs 2009-06-08 15:25:49.000000000 +1000
@@ -1202,6 +1202,10 @@
XSRETURN_EMPTY;
minsv = maxsv = ST(0);
+ if (items == 1) {
+ EXTEND (SP, 2);
+ goto done;
+ }
min = max = slu_sv_value(minsv);
for (i = 1; i < items; i += 2) {
@@ -1255,6 +1259,7 @@
}
}
}
+ done:
ST(0) = minsv;
ST(1) = maxsv;