from https://sourceforge.net/p/gens/patches/25/

--- gens.orig/src/gens/gens_core/cpu/68k/cpu_68k.c	2004-05-22 09:02:12.000000000 -0700
+++ gens/src/gens/gens_core/cpu/68k/cpu_68k.c	2005-03-21 10:52:24.000000000 -0800
@@ -24,9 +24,9 @@
 
 struct STARSCREAM_PROGRAMREGION M68K_Fetch[] = {
   {0x000000, 0x3FFFFF, (unsigned) 0x000000},
-  {0xFF0000, 0xFFFFFF, (unsigned) &Ram_68k[0] - 0xFF0000},
-  {0xF00000, 0xF0FFFF, (unsigned) &Ram_68k[0] - 0xF00000},
-  {0xEF0000, 0xEFFFFF, (unsigned) &Ram_68k[0] - 0xEF0000},
+  {0xFF0000, 0xFFFFFF, (unsigned) NULL},
+  {0xF00000, 0xF0FFFF, (unsigned) NULL},
+  {0xEF0000, 0xEFFFFF, (unsigned) NULL},
   {-1, -1, (unsigned) NULL},
   {-1, -1, (unsigned) NULL},
   {-1, -1, (unsigned) NULL}
@@ -60,7 +60,7 @@
 
 
 struct STARSCREAM_PROGRAMREGION S68K_Fetch[] = {
-  {0x000000, 0x07FFFF, (unsigned) &Ram_Prg[0]},
+  {0x000000, 0x07FFFF, (unsigned) NULL},
   {-1, -1, (unsigned) NULL},
   {-1, -1, (unsigned) NULL}
 };
@@ -109,6 +109,10 @@
 int
 M68K_Init (void)
 {
+  M68K_Fetch[1].offset=(unsigned) &Ram_68k[0] - 0xFF0000;
+  M68K_Fetch[2].offset=(unsigned) &Ram_68k[0] - 0xF00000;
+  M68K_Fetch[3].offset=(unsigned) &Ram_68k[0] - 0xEF0000;
+  
   memset (&Context_68K, 0, sizeof (Context_68K));
 
   Context_68K.s_fetch = Context_68K.u_fetch = Context_68K.fetch = M68K_Fetch;
@@ -134,6 +138,8 @@
 int
 S68K_Init (void)
 {
+  S68K_Fetch[0].offset=(unsigned) &Ram_Prg[0];
+  
   memset (&Context_68K, 0, sizeof (Context_68K));
 
   Context_68K.s_fetch = Context_68K.u_fetch = Context_68K.fetch = S68K_Fetch;