[perl #123954] Perl_pp_substcont: Assertion `((sv)->sv_flags & 0x00000400)' failed (pp_ctl.c:318)

# New Ticket Created by  Brian Carpenter 
# Please include the string:  [perl #123954]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=123954 >


I couldn't stay away. Built v5.21.10 (v5.21.9-43-g2c3f32a) with the following command line:

/Configure -des -Dusedevel -DDEBUGGING -Dcc=afl-gcc -Doptimize=-O2\ -g && AFL_HARDEN=1 make -j12 test-prep

Bug found with AFL (http://lcamtuf.coredump.cx/afl)

Valgrind:
perl: pp_ctl.c:318: Perl_pp_substcont: Assertion `((sv)->sv_flags & 0x00000400)' failed.
==12237== 
==12237== Process terminating with default action of signal 6 (SIGABRT): dumping core
==12237==    at 0x5B55165: raise (raise.c:64)
==12237==    by 0x5B583DF: abort (abort.c:92)
==12237==    by 0x5B4E310: __assert_fail (assert.c:81)
==12237==    by 0xB30ED4: Perl_pp_substcont (pp_ctl.c:318)
==12237==    by 0x7CD89E: Perl_runops_debug (dump.c:2237)
==12237==    by 0x53B808: perl_run (perl.c:2427)
==12237==    by 0x42B1C7: main (perlmain.c:116)

GDB:
gdb-peda$ file ~/perl/perl
gdb-peda$ set args test01-min
gdb-peda$ r
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
perl: pp_ctl.c:318: Perl_pp_substcont: Assertion `((sv)->sv_flags & 0x00000400)' failed.

Program received signal SIGABRT, Aborted.
[----------------------------------registers-----------------------------------]
RAX: 0x0 
RBX: 0x7fffffffe63b --> 0x736574006c726570 ('perl')
RCX: 0xffffffffffffffff 
RDX: 0x6 
RSI: 0xbed4 
RDI: 0xbed4 
RBP: 0x7ffff6ea9a07 --> 0x257325732500203a (': ')
RSP: 0x7fffffffdf18 --> 0x7ffff6d923e0 (<*__GI_abort+384>:	mov    rdx,QWORD PTR fs:0x10)
RIP: 0x7ffff6d8f165 (<*__GI_raise+53>:	cmp    rax,0xfffffffffffff000)
R8 : 0x7ffff7fdd700 (0x00007ffff7fdd700)
R9 : 0x2d29767328286020 (' `((sv)-')
R10: 0x8 
R11: 0x206 
R12: 0xef9f73 ("((sv)->sv_flags & 0x00000400)")
R13: 0xf6e8f0 ("Perl_pp_substcont")
R14: 0x7ffff6ea9a07 --> 0x257325732500203a (': ')
R15: 0x13e
EFLAGS: 0x206 (carry PARITY adjust zero sign trap INTERRUPT direction overflow)
[-------------------------------------code-------------------------------------]
   0x7ffff6d8f15b <*__GI_raise+43>:	movsxd rdi,eax
   0x7ffff6d8f15e <*__GI_raise+46>:	mov    eax,0xea
   0x7ffff6d8f163 <*__GI_raise+51>:	syscall 
=> 0x7ffff6d8f165 <*__GI_raise+53>:	cmp    rax,0xfffffffffffff000
   0x7ffff6d8f16b <*__GI_raise+59>:	ja     0x7ffff6d8f182 <*__GI_raise+82>
   0x7ffff6d8f16d <*__GI_raise+61>:	repz ret 
   0x7ffff6d8f16f <*__GI_raise+63>:	nop
   0x7ffff6d8f170 <*__GI_raise+64>:	test   eax,eax
[------------------------------------stack-------------------------------------]
0000| 0x7fffffffdf18 --> 0x7ffff6d923e0 (<*__GI_abort+384>:	mov    rdx,QWORD PTR fs:0x10)
0008| 0x7fffffffdf20 --> 0xef9f73 ("((sv)->sv_flags & 0x00000400)")
0016| 0x7fffffffdf28 --> 0x7ffff6eab9c1 --> 0x706c6568007325 ('%s')
0024| 0x7fffffffdf30 --> 0x7fffffffdf50 --> 0x3000000018 
0032| 0x7fffffffdf38 --> 0x13e 
0040| 0x7fffffffdf40 --> 0x7fffffffe040 --> 0x7fffffffe63b --> 0x736574006c726570 ('perl')
0048| 0x7fffffffdf48 --> 0x7ffff6dc3fe6 (<__fxprintf+310>:	lea    rsp,[rbp-0x20])
0056| 0x7fffffffdf50 --> 0x3000000018 
[------------------------------------------------------------------------------]
Legend: code, data, rodata, value
Stopped reason: SIGABRT
0x00007ffff6d8f165 in *__GI_raise (sig=<optimized out>) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
64	../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.

Test case that causes this failure is 22 bytes, here's a hexdump:
0000000 7730 6968 656c 7320 2f2f 6863 2872 5f24
0000010 2b2b 2f29 6567                         
0000016

• [perl #123954] Perl_pp_substcont: Assertion `((sv)->sv_flags & 0x00000400)' failed (pp_ctl.c:318) by Father Chrysostomos via RT
• [perl #123954] Perl_pp_substcont: Assertion `((sv)->sv_flags & 0x00000400)' failed (pp_ctl.c:318) by Brian Carpenter