From 531ec0bc39500f3036f2e81bb4e30e6ff45caf8b Mon Sep 17 00:00:00 2001
From: Tony Cook <tony@develop-help.com>
Date: Tue, 14 Apr 2015 15:59:03 +1000
Subject: fix cloning arrays with unused elements

ce0d59fd changed arrays to use NULL instead of &PL_sv_undef for
unused elements, unfortunately it missed updating sv_dup_common()'s
initialization of unused elements, leaving them as &PL_sv_undef.

This resulted in modification of read only value errors at runtime.

Origin: upstream, http://perl5.git.perl.org/perl.git/commit/902d16915db2735c3a41f15ef8d95cf300c31801
Bug: https://rt.perl.org/Public/Bug/Display.html?id=124127
Bug-Debian: https://bugs.debian.org/779357
Patch-Name: fixes/array-cloning.diff
---
 sv.c           | 2 +-
 t/op/threads.t | 8 +++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/sv.c b/sv.c
index af393bdeab..06db7d9b2c 100644
--- a/sv.c
+++ b/sv.c
@@ -12698,7 +12698,7 @@ S_sv_dup_common(pTHX_ const SV *const sstr, CLONE_PARAMS *const param)
 		    }
 		    items = AvMAX((const AV *)sstr) - AvFILLp((const AV *)sstr);
 		    while (items-- > 0) {
-			*dst_ary++ = &PL_sv_undef;
+			*dst_ary++ = NULL;
 		    }
 		}
 		else {
diff --git a/t/op/threads.t b/t/op/threads.t
index 67b5f4a713..bec210b9d2 100644
--- a/t/op/threads.t
+++ b/t/op/threads.t
@@ -9,7 +9,7 @@ BEGIN {
      skip_all_without_config('useithreads');
      skip_all_if_miniperl("no dynamic loading on miniperl, no threads");
 
-     plan(27);
+     plan(28);
 }
 
 use strict;
@@ -403,4 +403,10 @@ fresh_perl_is(
   'no crash when deleting $::{INC} in thread'
 );
 
+fresh_perl_is(<<'CODE', 'ok', 'no crash modifying extended array element');
+use threads;
+my @a = 1;
+threads->create(sub { $#a = 1; $a[1] = 2; print qq/ok\n/ })->join;
+CODE
+
 # EOF