for loops: protect GV/LVREF from premature free

In something like

    for $package_var (....) { ... }

or more experimentally,

    for \$lvref (....) { ... }

when entering the loop in pp_enteriter, perl would pop the GV/LVREF off
the stack, but didn't bump its refcount. Thus it was possible (if
unlikely) that it could be freed during the loop. In particular this
crashed:

    $f = "foo";
    for ${*$f} (1,2) {
        delete $main::{$f}; # delete the glob *foo
        ...;
    }

This will become more serious when the stack becomes refcounted, as
popping something off the stack will trigger a refcount decrement on it
and thus a possible immediate free of the GV.

This commit future-proofs for loops against this by ensuring that
the refcount of the SV referred to by cx->blk_loop.itervar_u.svp is
appropriately bumped up / down on entering / exiting the loop.

0 files changed, 0 insertions, 0 deletions