From: Yitzchak Scott-Thoennes <sthoenna@efn.org>
Date: Fri, 7 Mar 2003 13:12:49 +0000 (-0800)
Subject: Re: odd (or not so odd?) segmentation fault in 5.8.0
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=b77f7d40943072c6b8a82e9e0fbdcc2d346120ee;p=p5sagit%2Fp5-mst-13.2.git

Re: odd (or not so odd?) segmentation fault in 5.8.0
Message-ID: <RtQa+gzkg2kF092yn@efn.org>

p4raw-id: //depot/perl@18889
---

diff --git a/mg.c b/mg.c
index 941338b..98e4c09 100644
--- a/mg.c
+++ b/mg.c
@@ -133,6 +133,12 @@ Perl_mg_get(pTHX_ SV *sv)
 
 	if (!(mg->mg_flags & MGf_GSKIP) && vtbl && vtbl->svt_get) {
 	    CALL_FPTR(vtbl->svt_get)(aTHX_ sv, mg);
+
+	    /* guard against sv having been freed */
+	    if (SvTYPE(sv) == SVTYPEMASK) {
+		Perl_croak(aTHX_ "Tied variable freed while still in use");
+	    }
+
 	    /* Don't restore the flags for this entry if it was deleted. */
 	    if (mg->mg_flags & MGf_GSKIP)
 		(SSPTR(mgs_ix, MGS *))->mgs_flags = 0;
diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 3881288..cb314e9 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -3672,6 +3672,12 @@ target of the change to
 
 (F) The entry point function of threads->create() failed for some reason.
 
+=item Tied variable freed while still in use
+
+(F) An access method for a tied variable (e.g. FETCH) did something to
+free the variable.  Since continuing the current operation is likely
+to result in a coredump, Perl is bailing out instead.
+
 =item times not implemented
 
 (F) Your version of the C library apparently doesn't do times().  I
diff --git a/t/op/tie.t b/t/op/tie.t
index 6e73cee..49c189e 100755
--- a/t/op/tie.t
+++ b/t/op/tie.t
@@ -286,3 +286,12 @@ EXPECT
 7
 8
 0
+########
+#
+# FETCH freeing tie'd SV
+sub TIESCALAR { bless [] }
+sub FETCH { *a = \1; 1 }
+tie $a, 'main';
+print $a;
+EXPECT
+Tied variable freed while still in use at - line 6.