add stack extend to Perl_die_unwind()

When invoked via a scalar-context eval, die_unwind() was pushing
&PL_sv_undef without extending the stack first. It's been this way for
many years. Spotted by visual inspection while adding rpp_() code.

I could get a SEGV with the following code, but I haven't added it as a
test as it's highly sensitive to exactly what size stack is initially
allocated and the OS's malloc().

    my $x;
    my @a =
        ($x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,
         $x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,
         $x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,
         $x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,
         $x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,
         $x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,
         $x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,
         $x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,$x,
         scalar eval { die },
    );

diff --git a/pp_ctl.c b/pp_ctl.c
index 8c5a2c3..4120d09 100644 (file)
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -2020,6 +2020,7 @@ Perl_die_unwind(pTHX_ SV *msv)
             /* return false to the caller of eval */
             gimme = cx->blk_gimme;
             if (gimme == G_SCALAR) {
+                rpp_extend(1);
                 if (rpp_stack_is_rc())
                     rpp_push_1(&PL_sv_undef);
                 else