From a2637ca0a3fec01b80d7ea5ba62802354fd5e6f3 Mon Sep 17 00:00:00 2001
From: Father Chrysostomos <sprout@cpan.org>
Date: Mon, 11 Jul 2016 14:49:17 -0700
Subject: [PATCH] [perl #128597] Crash from gp_free/ckWARN_d
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See the explanation in the test added and in the RT ticket.

The solution is to make the warn macros check that PL_curcop
is non-null.

Signed-off-by: Petr Písař <ppisar@redhat.com>
---
 regen/warnings.pl |  6 ++++--
 t/op/gv.t         | 18 +++++++++++++++++-
 warnings.h        |  6 ++++--
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/regen/warnings.pl b/regen/warnings.pl
index 815c735..94cd7a4 100644
--- a/regen/warnings.pl
+++ b/regen/warnings.pl
@@ -358,8 +358,10 @@ EOM
 
   print $warn <<'EOM';
 
-#define isLEXWARN_on 	cBOOL(PL_curcop->cop_warnings != pWARN_STD)
-#define isLEXWARN_off	cBOOL(PL_curcop->cop_warnings == pWARN_STD)
+#define isLEXWARN_on \
+	cBOOL(PL_curcop && PL_curcop->cop_warnings != pWARN_STD)
+#define isLEXWARN_off \
+	cBOOL(!PL_curcop || PL_curcop->cop_warnings == pWARN_STD)
 #define isWARN_ONCE	(PL_dowarn & (G_WARN_ON|G_WARN_ONCE))
 #define isWARN_on(c,x)	(IsSet((U8 *)(c + 1), 2*(x)))
 #define isWARNf_on(c,x)	(IsSet((U8 *)(c + 1), 2*(x)+1))
diff --git a/t/op/gv.t b/t/op/gv.t
index d71fd0a..03ae46e 100644
--- a/t/op/gv.t
+++ b/t/op/gv.t
@@ -12,7 +12,7 @@ BEGIN {
 
 use warnings;
 
-plan(tests => 276 );
+plan(tests => 277 );
 
 # type coercion on assignment
 $foo = 'foo';
@@ -1153,6 +1153,22 @@ pass "No crash due to CvGV pointing to glob copy in the stash";
     is($c_125840, 1, 'RT #125840: $c=$d');
 }
 
+# [perl #128597] Crash when gp_free calls ckWARN_d
+# I am not sure this test even belongs in this file, as the crash was the
+# result of various features interacting.  But a call to ckWARN_d from
+# gv.c:gp_free triggered the crash, so this seems as good a place as any.
+# ‘die’ (or any abnormal scope exit) can cause the current cop to be freed,
+# if the subroutine containing the ‘die’ gets freed as a result.  That
+# causes PL_curcop to be set to NULL.  If a writable handle gets freed
+# while PL_curcop is NULL, then gp_free will call ckWARN_d while that con-
+# dition still holds, so ckWARN_d needs to know about PL_curcop possibly
+# being NULL.
+SKIP: {
+    skip_if_miniperl("No PerlIO::scalar on miniperl", 1);
+    runperl(prog => 'open my $fh, q|>|, \$buf;'
+                   .'my $sub = eval q|sub {exit 0}|; $sub->()');
+    is ($? & 127, 0,"[perl #128597] No crash when gp_free calls ckWARN_d");
+}
 
 __END__
 Perl
diff --git a/warnings.h b/warnings.h
index 337bef3..4d13732 100644
--- a/warnings.h
+++ b/warnings.h
@@ -115,8 +115,10 @@
 #define WARN_ALLstring			 "\125\125\125\125\125\125\125\125\125\125\125\125\125\125\125\125\125"
 #define WARN_NONEstring			 "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
 
-#define isLEXWARN_on 	cBOOL(PL_curcop->cop_warnings != pWARN_STD)
-#define isLEXWARN_off	cBOOL(PL_curcop->cop_warnings == pWARN_STD)
+#define isLEXWARN_on \
+	cBOOL(PL_curcop && PL_curcop->cop_warnings != pWARN_STD)
+#define isLEXWARN_off \
+	cBOOL(!PL_curcop || PL_curcop->cop_warnings == pWARN_STD)
 #define isWARN_ONCE	(PL_dowarn & (G_WARN_ON|G_WARN_ONCE))
 #define isWARN_on(c,x)	(IsSet((U8 *)(c + 1), 2*(x)))
 #define isWARNf_on(c,x)	(IsSet((U8 *)(c + 1), 2*(x)+1))
-- 
2.5.5