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Either POSIX is confused about WEXITSTATUS or I am #13292

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p5pRT opened this issue Sep 20, 2013 · 3 comments
Open

Either POSIX is confused about WEXITSTATUS or I am #13292

p5pRT opened this issue Sep 20, 2013 · 3 comments
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distro-Linux type-library

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@p5pRT
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p5pRT commented Sep 20, 2013

Migrated from rt.perl.org#119899 (status was 'open')

Searchable as RT119899$
@p5pRT
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p5pRT commented Sep 20, 2013

From @mauke

Created by @mauke

perldoc POSIX​:
...
  Macros WIFEXITED WEXITSTATUS WIFSIGNALED WTERMSIG WIFSTOPPED WSTOPSIG

  WIFEXITED WIFEXITED(${^CHILD_ERROR_NATIVE}) returns true if
  the child process exited normally ("exit()" or by
  falling off the end of "main()")

  WEXITSTATUS WEXITSTATUS(${^CHILD_ERROR_NATIVE}) returns the
  normal exit status of the child process (only
  meaningful if WIFEXITED(${^CHILD_ERROR_NATIVE}) is
  true)
...

This tells me that WEXITSTATUS and friends are supposed to be called with
${^CHILD_ERROR_NATIVE}, which is in an unknown / presumably system-specific
format, and not $?, which is always of the form $exit_status << 8 |
$killed_by_signal << 7 | $signal_number.

But looking at the implementation I see this (in POSIX.xs)​:

/* Background​: in most systems the low byte of the wait status
* is the signal (the lowest 7 bits) and the coredump flag is
* the eight bit, and the second lowest byte is the exit status.
* BeOS bucks the trend and has the bytes in different order.
* See beos/beos.c for how the reality is bent even in BeOS
* to follow the traditional. However, to make the POSIX
* wait W*() macros to work in BeOS, we need to unbend the
* reality back in place. --jhi */
/* In actual fact the code below is to blame here. Perl has an internal
* representation of the exit status ($?), which it re-composes from the
* OS's representation using the W*() POSIX macros. The code below
* incorrectly uses the W*() macros on the internal representation,
* which fails for OSs that have a different representation (namely BeOS
* and Haiku). WMUNGE() is a hack that converts the internal
* representation into the OS specific one, so that the W*() macros work
* as expected. The better solution would be not to use the W*() macros
* in the first place, though. -- Ingo Weinhold
*/
#if defined(__HAIKU__)
# define WMUNGE(x) (((x) & 0xFF00) >> 8 | ((x) & 0x00FF) << 8)
#else
# define WMUNGE(x) (x)
#endif

  RETVAL = WEXITSTATUS(WMUNGE(status));

The WMUNGE() part seems to assume an input in $? format, which has to be
"unmangled" in order to be forwarded to the platform-specific W*() macros.

This contradicts the documentation AIUI. Which is correct, the code/comments or
the documentation?

Perl Info 

Flags:
    category=library
    severity=low
    module=POSIX

This perlbug was built using Perl 5.12.1 - Thu Jun  3 20:09:15 CEST 2010
It is being executed now by  Perl 5.18.1 - Tue Aug 13 07:08:47 CEST 2013.

Site configuration information for perl 5.18.1:

Configured by mauke at Tue Aug 13 07:08:47 CEST 2013.

Summary of my perl5 (revision 5 version 18 subversion 1) configuration:
   
  Platform:
    osname=linux, osvers=3.5.7-gentoo, archname=i686-linux
    uname='linux nora 3.5.7-gentoo #5 preempt sat jan 26 16:46:10 cet 2013 i686 amd athlon(tm) 64 processor 3200+ authenticamd gnulinux '
    config_args=''
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=undef, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2 -flto',
    cppflags='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.8.1', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags ='-O2 -flto -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /lib/../lib /usr/lib/../lib /lib /usr/lib
    libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
    libc=/lib/libc-2.15.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.15'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -flto -L/usr/local/lib -fstack-protector'

Locally applied patches:
    SAVEARGV0 - disable magic open in <ARGV>


@INC for perl 5.18.1:
    /home/mauke/usr/local/lib/perl5/site_perl/5.18.1/i686-linux
    /home/mauke/usr/local/lib/perl5/site_perl/5.18.1
    /home/mauke/usr/local/lib/perl5/5.18.1/i686-linux
    /home/mauke/usr/local/lib/perl5/5.18.1
    .


Environment for perl 5.18.1:
    HOME=/home/mauke
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LC_COLLATE=POSIX
    LD_LIBRARY_PATH=/home/mauke/usr/local/lib
    LOGDIR (unset)
    PATH=/home/mauke/usr/perlbrew/bin:/home/mauke/usr/local/bin:/usr/local/bin:/usr/bin:/bin:/opt/bin:/usr/i686-pc-linux-gnu/gcc-bin/4.6.3:/opt/sun-jdk-1.4.2.13/bin:/opt/sun-jdk-1.4.2.13/jre/bin:/opt/sun-jdk-1.4.2.13/jre/javaws:/opt/dmd/bin:/usr/games/bin
    PERLBREW_BASHRC_VERSION=0.43
    PERLBREW_HOME=/home/mauke/.perlbrew
    PERLBREW_PATH=/home/mauke/usr/perlbrew/bin
    PERLBREW_ROOT=/home/mauke/usr/perlbrew
    PERLBREW_VERSION=0.27
    PERL_BADLANG (unset)
    PERL_UNICODE=SAL
    SHELL=/bin/bash

@p5pRT
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p5pRT commented Sep 20, 2013

From @leonerd

On Fri, 20 Sep 2013 05​:56​:32 -0700
l.mai@​web.de (via RT) <perlbug-followup@​perl.org> wrote​:

This contradicts the documentation AIUI. Which is correct, the
code/comments or the documentation?

The background to this question is whether it is always appropriate to
test things like

  if(WIFEXITED($?)) { printf "Exit code %d\n", WEXITSTATUS($?) }

--
Paul "LeoNerd" Evans

leonerd@​leonerd.org.uk
ICQ# 4135350 | Registered Linux# 179460
http​://www.leonerd.org.uk/

@p5pRT
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p5pRT commented Sep 20, 2013

The RT System itself - Status changed from 'new' to 'open'

@xenu xenu removed the affects-5.18 label Nov 19, 2021
@xenu xenu removed the Severity Low label Dec 29, 2021
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