Companion to #16601: cxinc would create uninitialized

PERL_CONTEXTs.  The bug was tickled by the test
lib/Math/BigInt/t/upgrade.t, the new test of recurse.t
added to check that I got the context stack extension right.
Also rewrite recurse.t to use test.pl.

p4raw-id: //depot/perl@16679

1 files changed, 7 insertions, 2 deletions

diff --git a/scope.c b/scope.c
index 4ff903fe3e..5ae9a31a9a 100644
--- a/scope.c
+++ b/scope.c
@@ -80,8 +80,8 @@ Perl_new_stackinfo(pTHX_ I32 stitems, I32 cxitems)
     si->si_cxmax = cxitems - 1;
     si->si_cxix = -1;
     si->si_type = PERLSI_UNDEF;
-    /* Needs to be Newz() because PUSHSUBST() in pp_subst()
-     * might otherwise read uninitialized heap. */
+    /* Needs to be Newz() instead of New() because PUSHSUBST()
+     * in pp_subst() might otherwise read uninitialized heap. */
     Newz(56, si->si_cxstack, cxitems, PERL_CONTEXT);
     return si;
 }
@@ -89,8 +89,13 @@ Perl_new_stackinfo(pTHX_ I32 stitems, I32 cxitems)
 I32
 Perl_cxinc(pTHX)
 {
+    IV old_max = cxstack_max;
     cxstack_max = GROW(cxstack_max);
     Renew(cxstack, cxstack_max + 1, PERL_CONTEXT);	/* XXX should fix CXINC macro */
+    /* Needs to Zero()ed because otherwise deep enough recursion
+     * (such as in lib/Math/BigInt/t/upgrade.t) will end up reading
+     * uninitialized heap. */
+    Zero(cxstack + old_max + 1, cxstack_max - old_max, PERL_CONTEXT);
     return cxstack_ix + 1;
 }