# HG changeset patch
# Parent adebc6b144a3a0cb9c22cc939431ace635414d0e

diff -r adebc6b144a3 cpu-defs.h
--- a/cpu-defs.h	Mon Aug 30 13:09:19 2010 -0400
+++ b/cpu-defs.h	Tue Aug 31 12:15:14 2010 -0400
@@ -60,6 +60,7 @@
 #define EXCP_HLT        0x10001 /* hlt instruction reached */
 #define EXCP_DEBUG      0x10002 /* cpu stopped after a breakpoint or singlestep */
 #define EXCP_HALTED     0x10003 /* cpu is halted (waiting for external event) */
+#define EXCP_TRIPLE     0x10004 /* cpu encountered triple fault */
 
 #define TB_JMP_CACHE_BITS 12
 #define TB_JMP_CACHE_SIZE (1 << TB_JMP_CACHE_BITS)
diff -r adebc6b144a3 gdbstub.c
--- a/gdbstub.c	Mon Aug 30 13:09:19 2010 -0400
+++ b/gdbstub.c	Tue Aug 31 12:15:14 2010 -0400
@@ -2610,3 +2610,8 @@
     return 0;
 }
 #endif
+
+int gdbserver_running(void)
+{
+    return gdbserver_state != NULL;
+}
diff -r adebc6b144a3 gdbstub.h
--- a/gdbstub.h	Mon Aug 30 13:09:19 2010 -0400
+++ b/gdbstub.h	Tue Aug 31 12:15:14 2010 -0400
@@ -26,6 +26,7 @@
 #else
 int gdbserver_start(const char *port);
 #endif
+int gdbserver_running(void);
 /* Get or set a register.  Returns the size of the register.  */
 typedef int (*gdb_reg_cb)(CPUState *env, uint8_t *buf, int reg);
 void gdb_register_coprocessor(CPUState *env,
diff -r adebc6b144a3 target-i386/op_helper.c
--- a/target-i386/op_helper.c	Mon Aug 30 13:09:19 2010 -0400
+++ b/target-i386/op_helper.c	Tue Aug 31 12:15:14 2010 -0400
@@ -1297,8 +1297,18 @@
 
         qemu_log_mask(CPU_LOG_RESET, "Triple fault\n");
 
+#if 0
         qemu_system_reset_request();
         return EXCP_HLT;
+#else
+        // QEMU traditionally resets the machine on triple fault
+        // because programs written for 286 protected mode would exit
+        // protected mode by intentionally triple faulting the machine
+        // (after setting the boot vector to point to their code).
+        // This sucks for debugging programs that were written after
+        // 1985, so we instead halt the machine for inspection.
+        return EXCP_TRIPLE;
+#endif
     }
 #endif
 
diff -r adebc6b144a3 vl.c
--- a/vl.c	Mon Aug 30 13:09:19 2010 -0400
+++ b/vl.c	Tue Aug 31 12:15:14 2010 -0400
@@ -4057,6 +4057,15 @@
         else if (env->stop)
             break;
 
+        if (ret == EXCP_TRIPLE) {
+            cpu_dump_state(env, stderr, fprintf, 0);
+            fprintf(stderr, "Triple fault.  Halting for inspection via QEMU monitor.\n");
+            if (gdbserver_running())
+                ret = EXCP_DEBUG;
+            else
+                vm_stop(0);
+        }
+
         if (ret == EXCP_DEBUG) {
             gdb_set_stop_cpu(env);
             debug_requested = 1;