[perl #117947] Verify lvalueness of XSUBs at run time

If the sub is not visible at compile time, the op tree is flagged such
that pp_entersub will know whether to check the lvalueness of the
called sub.

That check has been in pp_entersub since da1dff9483c.  When I moved
it to pp_entersub in that commit, I only added it to the pure-Perl
branch, not to the XS branch, allowing all XSUBs to be treated as
lvalues if they are not visible at compile time.

1 files changed, 6 insertions, 0 deletions

diff --git a/pp_hot.c b/pp_hot.c
index dd9e5f15be..157c469122 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -2847,6 +2847,12 @@ try_autoload:
 
 	PUTBACK;
 
+	if (((PL_op->op_private
+	       & PUSHSUB_GET_LVALUE_MASK(Perl_is_lvalue_sub)
+             ) & OPpENTERSUB_LVAL_MASK) == OPpLVAL_INTRO &&
+	    !CvLVALUE(cv))
+	    DIE(aTHX_ "Can't modify non-lvalue subroutine call");
+
 	if (!hasargs) {
 	    /* Need to copy @_ to stack. Alternative may be to
 	     * switch stack to @_, and copy return values