From de7f0d6489e03b987b71b196eaf7135143111679 Mon Sep 17 00:00:00 2001
From: Tee-Kiah Chia <tkchia@users.noreply.github.com>
Date: Wed, 28 Jul 2021 17:13:44 +0000
Subject: [PATCH] task: don't zero parent_psp on 0x26

Patch ported from
  * https://github.com/dosemu2/fdpp/commit/f49252ac6b89a7bee0dd5ac90b9509918c19dd33
See
  * https://github.com/dosemu2/fdpp/issues/112
  * https://github.com/FDOS/kernel/issues/38
---
 kernel/task.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/task.c b/kernel/task.c
index 220cc0e..bcfafb5 100644
--- a/kernel/task.c
+++ b/kernel/task.c
@@ -224,8 +224,13 @@ void new_psp(seg para, seg cur_psp)
   p->ps_isv23 = getvec(0x23);
   /* critical error address                               */
   p->ps_isv24 = getvec(0x24);
+  /* RBIL is wrong on zeroing parent_psp, and in fact some
+   * progs (Alpha Waves game, https://github.com/stsp/fdpp/issues/112)
+   * won't work if its zeroed. */
+#if 0
   /* parent psp segment set to 0 (see RBIL int21/ah=26)   */
   p->ps_parent = 0;
+#endif
   /* default system version for int21/ah=30               */
   p->ps_retdosver = (os_setver_minor << 8) + os_setver_major;
 }