Index: class.c
==================================================================
--- class.c
+++ class.c
@@ -637,10 +637,11 @@
 static void nxttok(void) {
   if(pushback) {
     pushback=0;
     return;
   }
+  if(StackProtection()) fatal("Stack overflow\n");
   again:
   nxttok1();
   if(tokent&TF_EOF) {
     if(inpstack) {
       InputStack s=*inpstack;

Index: exec.c
==================================================================
--- exec.c
+++ exec.c
@@ -2,10 +2,11 @@
 gcc ${CFLAGS:--s -O2} -c exec.c `sdl-config --cflags`
 exit
 #endif
 
 #include "SDL.h"
+#include <setjmp.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include "sqlite3.h"
 #include "smallxrm.h"
@@ -14,5 +15,13 @@
 Uint32 generation_number;
 Object*objects;
 Uint32 nobjects;
 Value globals[0x800];
 
+static jmp_buf my_env;
+static int my_error;
+
+int execute_turn(int key) {
+  if(setjmp(my_env)) return my_error;
+  
+  return 0;
+}

Index: heromesh.h
==================================================================
--- heromesh.h
+++ heromesh.h
@@ -39,10 +39,29 @@
 extern xrm_db*resourcedb;
 extern const char*basefilename;
 extern xrm_quark optionquery[16];
 extern char main_options[128];
 extern Uint8 message_trace[0x4100/8];
+
+#ifdef __GNUC__
+extern char stack_protect_mode;
+extern void*stack_protect_mark;
+extern void*stack_protect_low;
+extern void*stack_protect_high;
+#define StackProtection() (stack_protect_mode && ( \
+  stack_protect_mode=='<' ? (__builtin_frame_address(0)<stack_protect_mark) : \
+  stack_protect_mode=='>' ? (__builtin_frame_address(0)>stack_protect_mark) : \
+  stack_protect_mode=='?' ? ({ \
+    if(__builtin_frame_address(0)<stack_protect_low) stack_protect_low=__builtin_frame_address(0); \
+    if(__builtin_frame_address(0)>stack_protect_high) stack_protect_high=__builtin_frame_address(0); \
+    0; \
+  }) : \
+  stack_protect_mode=='!' ? 1 : \
+0))
+#else
+#define StackProtection() 0
+#endif
 
 unsigned char*read_lump(int sol,int lvl,long*sz,sqlite3_value**us);
 void write_lump(int sol,int lvl,long sz,const unsigned char*data);
 void set_cursor(int id);
 

Index: main.c
==================================================================
--- main.c
+++ main.c
@@ -41,10 +41,17 @@
 xrm_db*resourcedb;
 const char*basefilename;
 xrm_quark optionquery[16];
 char main_options[128];
 Uint8 message_trace[0x4100/8];
+
+#ifdef __GNUC__
+char stack_protect_mode=0;
+void*stack_protect_mark;
+void*stack_protect_low;
+void*stack_protect_high;
+#endif
 
 static const char*globalclassname;
 static SDL_Cursor*cursor[77];
 static FILE*levelfp;
 static FILE*solutionfp;
@@ -561,10 +568,30 @@
     if(n>=m) fatal("Too long SQL statement\n");
   }
   if(n) fatal("Unterminated SQL statement\n");
   free(txt);
 }
+
+#ifdef __GNUC__
+static void test_stack_protection(void) {
+  fprintf(stderr,"Stack protection final values: %p %p %p\n",stack_protect_mark,stack_protect_low,stack_protect_high);
+}
+
+static void set_stack_protection(void) {
+  const char*v;
+  optionquery[1]=Q_stackProtection;
+  v=xrm_get_resource(resourcedb,optionquery,optionquery,2);
+  if(!v || !*v) return;
+  stack_protect_mode=*v;
+  if(*v=='?') {
+    fprintf(stderr,"Stack protection test mode: %p\n",stack_protect_mark);
+    stack_protect_low=stack_protect_high=stack_protect_mark;
+    atexit(test_stack_protection);
+  }
+  if(v[1]) stack_protect_mark=((char*)stack_protect_mark)+strtoll(v+1,0,0);
+}
+#endif
 
 int main(int argc,char**argv) {
   int optind=1;
   while(argc>optind && argv[optind][0]=='-') {
     int i;
@@ -583,17 +610,21 @@
     globalclassname=argv[optind++]+1;
   } else if(find_globalclassname()) {
     globalclassname=strrchr(basefilename,'/');
     globalclassname=globalclassname?globalclassname+1:basefilename;
   }
+  if(!main_options['c']) load_options();
+  if(argc>optind) read_options(argc-optind,argv+optind);
+  *optionquery=xrm_make_quark(globalclassname,0)?:xrm_anyq;
+#ifdef __GNUC__
+  stack_protect_mark=__builtin_frame_address(0);
+  set_stack_protection();
+#endif
   if(main_options['c']) {
     load_classes();
     return 0;
   }
-  load_options();
-  if(argc>optind) read_options(argc-optind,argv+optind);
-  *optionquery=xrm_make_quark(globalclassname,0)?:xrm_anyq;
   init_sql();
   load_key_bindings();
   init_screen();
   load_pictures();
   if(main_options['T']) {

Index: quarks
==================================================================
--- quarks
+++ quarks
@@ -207,6 +207,7 @@
 sqlPowerSafe
 
 ! Miscellaneous
 level
 tracePrefix
+stackProtection
 

Index: quarks.h
==================================================================
--- quarks.h
+++ quarks.h
@@ -172,10 +172,11 @@
 #define Q_sqlSmallAllocations 173
 #define Q_sqlCoveringIndexScan 174
 #define Q_sqlPowerSafe 175
 #define Q_level 176
 #define Q_tracePrefix 177
+#define Q_stackProtection 178
 static const char*const global_quarks[]={
   "screenWidth",
   "screenHeight",
   "palette",
   "popupColors",
@@ -349,10 +350,11 @@
   "sqlSmallAllocations",
   "sqlCoveringIndexScan",
   "sqlPowerSafe",
   "level",
   "tracePrefix",
+  "stackProtection",
 0};
 #ifdef HEROMESH_BINDINGS
 static const SDLKey quark_to_key[Q_undo+1-Q_backspace]={
 SDLK_BACKSPACE,
 SDLK_TAB,