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[perl #68328] debugger completely breaks lvalue subs/xs functions

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From:
perlbug-followup
Date:
August 8, 2009 09:32
Subject:
[perl #68328] debugger completely breaks lvalue subs/xs functions
Message ID:
rt-3.6.HEAD-2466-1249725718-844.68328-75-0@perl.org
# New Ticket Created by  perlbug@plan9.de 
# Please include the string:  [perl #68328]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=68328 >



This is a bug report for perl from perlbug@plan9.de,
generated with the help of perlbug 1.36 running under perl 5.10.0.


-----------------------------------------------------------------
[Please enter your report here]

I found that JSON::XS version 2.24 works differently under the debugger
then without it.

It turns out that this xs function failed to work:

   SV *incr_text (JSON *self)
           ATTRS: lvalue
           CODE:
           ...
           RETVAL = self->incr_text ? SvREFCNT_inc (self->incr_text) : &PL_sv_undef;
           OUTPUT:
           RETVAL

specifically, this perl statement had no effect:

   $self->incr_text = "";

This only happened when running under the debugger (perl -d).

This works aorund the issue:

   CvNODEBUG_on (get_cv ("JSON::XS::incr_text", 0)); /* otherwise calling scope can be the debugger */

(shameless feature request: it would be nice if one could set lvalue and
nodebug on xs, I need this attribute on a lot of functions to work around
debugger bugs).

Apparently the debugger breaks lvalue subs. In fact, the effect is
reproducable easily from within perl:

   $x = 5;
   sub k : lvalue { $x }  
   k = 7;
   die $x;

This prints 5 under the debugger, and 7 without it.

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=library
    severity=low
---
Site configuration information for perl 5.10.0:

Configured by Marc Lehmann at Sat Feb 21 02:30:27 CET 2009.

Summary of my perl5 (revision 5 version 10 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.6.24-etchnhalf.1-amd64, archname=amd64-linux
    uname='linux cerebro 2.6.24-etchnhalf.1-amd64 #1 smp mon jul 21 10:36:02 utc 2008 x86_64 gnulinux '
    config_args='-Duselargefiles -Dxxxxuse64bitint -Uuse64bitall -Dusemymalloc=n -Dcc=gcc -Dccflags=-ggdb -gdwarf-2 -g3 -Dcppflags=-DPERL_ARENA_SIZE=16368 -D_GNU_SOURCE -I/opt/include -Doptimize=-O6 -msse2 -funroll-loops -fno-strict-aliasing -Dcccdlflags=-fPIC -Dldflags=-L/opt/perl/lib -L/opt/lib -Dlibs=-ldl -lm -lcrypt -Darchname=amd64-linux -Dprefix=/opt/perl -Dprivlib=/opt/perl/lib/perl5 -Darchlib=/opt/perl/lib/perl5 -Dvendorprefix=/opt/perl -Dvendorlib=/opt/perl/lib/perl5 -Dvendorarch=/opt/perl/lib/perl5 -Dsiteprefix=/opt/perl -Dsitelib=/opt/perl/lib/perl5 -Dsitearch=/opt/perl/lib/perl5 -Dsitebin=/opt/perl/bin -Dman1dir=/opt/perl/man/man1 -Dman3dir=/opt/perl/man/man3 -Dsiteman1dir=/opt/perl/man/man1 -Dsiteman3dir=/opt/perl/man/man3 -Dman1ext=1 -Dman3ext=3 -Dpager=/usr/bin/less -Uafs -Uusesfio -Uusenm -Uuseshrplib -Dd_dosuid -Dusethreads=undef -Duse5005threads=undef -Duseithreads=undef -Dusemultiplicity=undef -Demail=perl-binary@plan9.de -Dcf_email=perl-binary@plan9.de -D!
 cf_by=Marc Lehmann -Dlocincpth=/opt/perl/include /opt/include -Dmyhostname=localhost -Dmultiarch=undef -Dbin=/opt/perl/bin -Dxxxusedevel -DxxxDEBUGGING -Dxxxuse_debugging_perl -Dxxxuse_debugmalloc -des'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='gcc', ccflags ='-ggdb -gdwarf-2 -g3 -fno-strict-aliasing -pipe -I/opt/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O6 -msse2 -funroll-loops -fno-strict-aliasing',
    cppflags='-DPERL_ARENA_SIZE=16368 -D_GNU_SOURCE -I/opt/include -ggdb -gdwarf-2 -g3 -fno-strict-aliasing -pipe -I/opt/include'
    ccversion='', gccversion='4.3.2', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='gcc', ldflags ='-L/opt/perl/lib -L/opt/lib -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib /lib64 /usr/lib64
    libs=-ldl -lm -lcrypt
    perllibs=-ldl -lm -lcrypt
    libc=/lib/libc-2.7.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.7'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O6 -msse2 -funroll-loops -fno-strict-aliasing -L/opt/perl/lib -L/opt/lib -L/usr/local/lib'

Locally applied patches:
    http://public.activestate.com/cgi-bin/perlbrowse/p/34209
    http://public.activestate.com/cgi-bin/perlbrowse/p/34507
    http://www.gossamer-threads.com/lists/perl/porters/232549
    embed.fnc:Perl_vcroak NULLOK

---
@INC for perl 5.10.0:
    /root/src/sex
    /opt/perl/lib/perl5
    /opt/perl/lib/perl5
    /opt/perl/lib/perl5
    /opt/perl/lib/perl5
    /opt/perl/lib/perl5
    .

---
Environment for perl 5.10.0:
    HOME=/root
    LANG (unset)
    LANGUAGE (unset)
    LC_CTYPE=en_US.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/root/s2:/root/s:/opt/bin:/opt/sbin:/bin:/sbin:/usr/bin:/usr/sbin:/usr/X11/bin:/usr/games:/usr/local/bin:/usr/local/sbin:/root/pserv:.
    PERL5LIB=/root/src/sex
    PERL5_CPANPLUS_CONFIG=/root/.cpanplus/config
    PERLDB_OPTS=ornaments=0
    PERL_ANYEVENT_DBI_TESTS=1
    PERL_ANYEVENT_EDNS0=1
    PERL_ANYEVENT_NET_TESTS=1
    PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6
    PERL_ANYEVENT_STRICT=1
    PERL_BADLANG (unset)
    PERL_UNICODE=0
    SHELL=/bin/bash


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