add a stack extend check to pp_entersub for XS subs

This allows us to report the XSUB involved by name (or at least by
filename if it's anonymous) in the likely case that it was an XSUB
that failed to extend the stack.

1 files changed, 15 insertions, 0 deletions

diff --git a/pp_hot.c b/pp_hot.c
index ee6535ca75..b891d79519 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -4420,6 +4420,21 @@ PP(pp_entersub)
 	assert(CvXSUB(cv));
 	CvXSUB(cv)(aTHX_ cv);
 
+#if defined DEBUGGING && !defined DEBUGGING_RE_ONLY
+        /* This duplicates the check done in runops_debug(), but provides more
+         * information in the common case of the fault being with an XSUB.
+         *
+         * It should also catch an XSUB pushing more than it extends
+         * in scalar context.
+        */
+        if (PL_curstackinfo->si_stack_hwm < PL_stack_sp - PL_stack_base)
+            Perl_croak_nocontext(
+                "panic: XSUB %s::%s (%s) failed to extend arg stack: "
+                "base=%p, sp=%p, hwm=%p\n",
+                    HvNAME(GvSTASH(CvGV(cv))), GvNAME(CvGV(cv)), CvFILE(cv),
+                    PL_stack_base, PL_stack_sp,
+                    PL_stack_base + PL_curstackinfo->si_stack_hwm);
+#endif
 	/* Enforce some sanity in scalar context. */
 	if (is_scalar) {
             SV **svp = PL_stack_base + markix + 1;