[perl #130622] op.c:1772: Perl_op_lvalue_flags: Assertion`(o->op_flags & OPf_WANT) != OPf_WANT_VOID' failed

# New Ticket Created by  Sergey Aleynikov 
# Please include the string:  [perl #130622]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=130622 >


This is a bug report for perl from sergey.aleynikov@gmail.com,
generated with the help of perlbug 1.40 running under perl 5.25.9.


-----------------------------------------------------------------
[Please describe your issue here]

While fuzzing perl v5.25.8-216-gfbceb79751 built with afl and run
under libdislocator, I found the following program

printf my(%c):_

to cause an assertion failure, even when run under -c for a syntax
check. This is a regression between v5.14.0 and v5.16.0,
bisect points to

69974ce61d7459da5eda22eb31d730128757db37 is the first bad commit
commit 69974ce61d7459da5eda22eb31d730128757db37
Author: Father Chrysostomos <sprout@cpan.org>
Date:   Sat Dec 31 23:24:57 2011 -0800

    [perl #103492] Give lvalue cx to (s)printf args

    Or potential lvalue context, like function calls.

    The %n format code’s existence renders these two very much like func-
    tion calls, as they can modify their arguments.

    This allows sprintf("...%n", substr ...) to work.

GDB info about the crash location:

(gdb) bt
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:58
#1  0x00007f27fd71c40a in __GI_abort () at abort.c:89
#2  0x00007f27fd713e47 in __assert_fail_base (fmt=<optimized out>,
assertion=assertion@entry=0x7f27feda5f70 "(o->op_flags & OPf_WANT) !=
OPf_WANT_VOID",
    file=file@entry=0x7f27feda452e "op.c", line=line@entry=2877,
function=function@entry=0x7f27fedaaab0 <__PRETTY_FUNCTION__.15847>
"Perl_op_lvalue_flags")
    at assert.c:92
#3  0x00007f27fd713ef2 in __GI___assert_fail (assertion=0x7f27feda5f70
"(o->op_flags & OPf_WANT) != OPf_WANT_VOID", file=0x7f27feda452e
"op.c", line=2877,
    function=0x7f27fedaaab0 <__PRETTY_FUNCTION__.15847>
"Perl_op_lvalue_flags") at assert.c:101
#4  0x00007f27fea5b5e7 in Perl_op_lvalue_flags (o=0x7f27fff48a30,
type=239, flags=0) at op.c:2877
#5  0x00007f27fea59c9b in S_modkids (o=0x7f27fff47350, type=239) at op.c:2369
#6  0x00007f27fea80ffa in Perl_ck_listiob (o=0x7f27fff47350) at op.c:10468
#7  0x00007f27fea63357 in Perl_op_convert_list (type=239, flags=0,
o=0x7f27fff47350) at op.c:4802
#8  0x00007f27feb16156 in Perl_yyparse (gramtype=258) at perly.y:883
#9  0x00007f27fea9733a in S_parse_body (env=0x0, xsinit=0x7f27fea52de8
<xs_init>) at perl.c:2376
#10 0x00007f27fea9569f in perl_parse (my_perl=0x7f27fff26010,
xsinit=0x7f27fea52de8 <xs_init>, argc=3, argv=0x7fffbd27a108, env=0x0)
at perl.c:1691
#11 0x00007f27fea52d26 in main (argc=3, argv=0x7fffbd27a108,
env=0x7fffbd27a128) at perlmain.c:121

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=low
---
Site configuration information for perl 5.25.9:

Configured by root at Sat Jan 14 02:25:05 MSK 2017.

Summary of my perl5 (revision 5 version 25 subversion 9) configuration:
  Commit id: cbe2fc5001aa59cdc73e04cc35e097a2ecfbeec0
  Platform:
    osname=linux
    osvers=3.16.0-4-amd64
    archname=x86_64-linux
    uname='linux dorothy 3.16.0-4-amd64 #1 smp debian 3.16.36-1+deb8u2
(2016-10-19) x86_64 gnulinux '
    config_args='-des -Dusedevel -DDEBUGGING -Dcc=afl-clang-fast
-Doptimize=-O0 -g -ggdb3'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    bincompat5005=undef
  Compiler:
    cc='afl-clang-fast'
    ccflags ='-DDEBUGGING -fno-strict-aliasing -pipe
-fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE
-D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
    optimize='-O0 -g -ggdb3'
    cppflags='-DDEBUGGING -fno-strict-aliasing -pipe
-fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='4.2.1 Compatible Clang 3.9.1 (tags/RELEASE_391/rc2)'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='afl-clang-fast'
    ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/llvm-3.9/bin/../lib/clang/3.9.1/lib
/usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu
/lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
    libs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.24.so
    so=so
    useshrplib=false
    libperl=libperl.a
    gnulibc_version='2.24'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E'
    cccdlflags='-fPIC'
    lddlflags='-shared -O0 -g -ggdb3 -L/usr/local/lib -fstack-protector-strong'


---
@INC for perl 5.25.9:
    lib
    /usr/local/lib/perl5/site_perl/5.25.9/x86_64-linux
    /usr/local/lib/perl5/site_perl/5.25.9
    /usr/local/lib/perl5/5.25.9/x86_64-linux
    /usr/local/lib/perl5/5.25.9

---
Environment for perl 5.25.9:
    HOME=/home/afl
    LANG=en_US.UTF-8
    LANGUAGE=en_US:en
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/afl/perlbrew/bin:/home/afl/perlbrew/perls/perl-5.22.1/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
    PERLBREW_BASHRC_VERSION=0.78
    PERLBREW_HOME=/home/afl/.perlbrew
    PERLBREW_MANPATH=/home/afl/perlbrew/perls/perl-5.22.1/man
    PERLBREW_PATH=/home/afl/perlbrew/bin:/home/afl/perlbrew/perls/perl-5.22.1/bin
    PERLBREW_PERL=perl-5.22.1
    PERLBREW_ROOT=/home/afl/perlbrew
    PERLBREW_VERSION=0.78
    PERL_BADLANG (unset)
    SHELL=/usr/bin/zsh

• [perl #130622] op.c:1772: Perl_op_lvalue_flags: Assertion`(o->op_flags & OPf_WANT) != OPf_WANT_VOID' failed by Sergey Aleynikov