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[perl #119555] require should not clobber $! and $^E on success
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From:
Christian Millour
Date:
September 4, 2013 16:45
Subject:
[perl #119555] require should not clobber $! and $^E on success
Message ID:
rt-3.6.HEAD-1873-1378114129-1728.119555-75-0@perl.org
# New Ticket Created by Christian Millour
# Please include the string: [perl #119555]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org:443/rt3/Ticket/Display.html?id=119555 >
This is a bug report for perl from cm.perl@abtela.com,
generated with the help of perlbug 1.39 running under perl 5.19.4.
-----------------------------------------------------------------
[Please describe your issue here]
On success, require resets $! and clobbers $^E (on platforms where $^E
is distinct from $!, such as Windows). It would be better to restore the
previous values of $! and $^E.
In the process of foraging through @INC, require may try to open several
files, and when it succeeds on step N, $! and $^E carry the failure
codes for step N-1. Such failures are however part of the normal working
of require. There is no reason to report them to the user. This
consideration might have motivated the resetting of $! (although the
exact ratinale is unclear, see
http://www.nntp.perl.org/group/perl.perl5.porters/2012/12/msg197015.html).
In any case $^E was left alone, and for the sake of consistency we might
consider resetting it also.
But resetting $! (and $^E) is a *bad thing* as it interferes with error
reporting. A number of core and CPAN modules use the following idiom (or
variants thereof) to implement 'lazy loading' of Carp :
sub croak {
require Carp;
goto &Carp::croak;
}
The problem here is that on first invocation (assuming Carp has not been
loaded elsewhere), $! and $^E will have been corrupted to unusable
values, as the following demonstrates :
Taisha:/cygdrive/d/perls/blead/perl-git/win32 $ cat
e:/cm/perl/tests/badcarp/require_clobbering_errno.pl
use strict;
use warnings;
sub croak {
require Carp;
goto &Carp::croak;
}
for (1 .. 3) {
eval {
rmdir 'notempty'
or croak '$! = ', 0+$!, ', $^E = ', 0+$^E, "\n";
1;
} or do {
my @msg = split /\n/, $@;
print '$@ : "', $msg[0], '"', "\n";
print '$! : ', 0+$! , " ($!)\n";
print '$^E : ', 0+$^E, " ($^E)\n";
print "-----\n";
}
}
Taisha:/cygdrive/d/perls/blead/perl-git/win32 $ ../perl
e:/cm/perl/tests/badcarp/require_clobbering_errno.pl
$@ : "$! = 41, $^E = 145"
$! : 0 ()
$^E : 6 (Descripteur non valide)
-----
$@ : "$! = 41, $^E = 145"
$! : 41 (Directory not empty)
$^E : 145 (Le répertoire n'est pas vide)
-----
$@ : "$! = 41, $^E = 145"
$! : 41 (Directory not empty)
$^E : 145 (Le répertoire n'est pas vide)
-----
Taisha:/cygdrive/d/perls/blead/perl-git/win32 $
Recent work on Carp (commit cbd58baf5927dd469f38f80a7c76c8011150b6c5)
ensured that croak and confess hand out uncorrupted values of $! and
$^E, thus giving access to their numerical values for programmatic error
recovery (see
http://www.nntp.perl.org/group/perl.perl5.porters/2013/08/msg206736.html
and
http://www.nntp.perl.org/group/perl.perl5.porters/2012/12/msg197017.html
for a rationale).
In line with this effort, and considering the problem outlined above,
require should do the right thing and restore on success the values of
$! and $^E as they were on invocation.
ALTERNATIVE
If there is a compelling reason to keep having require corrupt^Hreset
$!, then $^E should probably also be reset for consistency (and both
resets should be documented). In addition, the idiom above should be
recast as
sub croak {
{ local ($!, $^E); require Carp }
goto &Carp::croak;
}
here is an indicative list of core files to patch :
dist/SelfLoader/lib/SelfLoader.pm
lib/POSIX.pm
lib/open.pm
lib/File/Compare.pm
lib/File/Copy.pm
lib/File/Path.pm
lib/attributes.pm
lib/_charnames.pm
lib/Tie/Memoize.pm
lib/SelfLoader.pm
lib/Term/Cap.pm
cpan/File-Path/lib/File/Path.pm
cpan/Term-Cap/Cap.pm
ext/attributes/attributes.pm
ext/POSIX/lib/POSIX.pm
ext/Tie-Memoize/lib/Tie/Memoize.pm
WORKAROUND
The problem above can be avoided by loading Carp as early as possible in
the main script (which I have been doing for years, after having been
bitten by this exact bug).
[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
category=core
severity=low
---
Site configuration information for perl 5.19.4:
Configured by cm at Mon Sep 2 01:34:49 2013.
Summary of my perl5 (revision 5 version 19 subversion 4) configuration:
Commit id: cbd58baf5927dd469f38f80a7c76c8011150b6c5
Platform:
osname=MSWin32, osvers=4.0, archname=MSWin32-x64-multi-thread
uname=''
config_args='undef'
hint=recommended, useposix=true, d_sigaction=undef
useithreads=define, usemultiplicity=define
useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
use64bitint=define, use64bitall=undef, uselongdouble=undef
usemymalloc=n, bincompat5005=undef
Compiler:
cc='gcc', ccflags =' -s -O2 -DWIN32 -DWIN64 -DCONSERVATIVE
-DPERL_TEXTMODE_SCRIPTS -DPERL_IMPLICIT_CONTEXT -DPERL_IMPLICIT_SYS
-DUSE_PERLIO -fno-strict-aliasing -mms-bitfields',
optimize='-s -O2',
cppflags='-DWIN32'
ccversion='', gccversion='4.6.3', gccosandvers=''
intsize=4, longsize=4, ptrsize=8, doublesize=8, byteorder=12345678
d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
ivtype='long long', ivsize=8, nvtype='double', nvsize=8,
Off_t='long long', lseeksize=8
alignbytes=8, prototype=define
Linker and Libraries:
ld='g++', ldflags ='-s -L"d:\perls\blead\perl\lib\CORE"
-L"C:\MinGW\lib"'
libpth=C:\MinGW\lib
libs=-lmoldname -lkernel32 -luser32 -lgdi32 -lwinspool -lcomdlg32
-ladvapi32 -lshell32 -lole32 -loleaut32 -lnetapi32 -luuid -lws2_32 -lmpr
-lwinmm -lversion -lodbc32 -lodbccp32 -lcomctl32
perllibs=-lmoldname -lkernel32 -luser32 -lgdi32 -lwinspool
-lcomdlg32 -ladvapi32 -lshell32 -lole32 -loleaut32 -lnetapi32 -luuid
-lws2_32 -lmpr -lwinmm -lversion -lodbc32 -lodbccp32 -lcomctl32
libc=, so=dll, useshrplib=true, libperl=libperl519.a
gnulibc_version=''
Dynamic Linking:
dlsrc=dl_win32.xs, dlext=dll, d_dlsymun=undef, ccdlflags=' '
cccdlflags=' ', lddlflags='-mdll -s
-L"d:\perls\blead\perl\lib\CORE" -L"C:\MinGW\lib"'
---
@INC for perl 5.19.4:
d:/perls/blead/perl/site/lib
d:/perls/blead/perl/lib
.
---
Environment for perl 5.19.4:
CYGWIN=nodosfilewarning
HOME=e:/cm
LANG (unset)
LANGUAGE (unset)
LD_LIBRARY_PATH (unset)
LOGDIR (unset)
PATH=C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;c:\strawberry-perl-5.16.1.1-64bit-portable\c\bin
PERL_BADLANG (unset)
SHELL (unset)
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[perl #119555] require should not clobber $! and $^E on success
by Christian Millour