[4/6] Handle CPU interrupts by inline checking of a flag

diff --git a/cpu-exec.c b/cpu-exec.c
index e80626a..6f4cc36 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -64,6 +64,12 @@  static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, uint8_t *tb_ptr)
         TranslationBlock *tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
         cpu_pc_from_tb(env, tb);
     }
+    if ((next_tb & TB_EXIT_MASK) == TB_EXIT_REQUESTED) {
+        /* We were asked to stop executing TBs (probably a pending
+         * interrupt. We've now stopped, so clear the flag.
+         */
+        cpu->tcg_exit_req = 0;
+    }
     return next_tb;
 }
 
@@ -608,7 +614,20 @@  int cpu_exec(CPUArchState *env)
                     tc_ptr = tb->tc_ptr;
                     /* execute the generated code */
                     next_tb = cpu_tb_exec(cpu, tc_ptr);
-                    if ((next_tb & TB_EXIT_MASK) == TB_EXIT_ICOUNT_EXPIRED) {
+                    switch (next_tb & TB_EXIT_MASK) {
+                    case TB_EXIT_REQUESTED:
+                        /* Something asked us to stop executing
+                         * chained TBs; just continue round the main
+                         * loop. Whatever requested the exit will also
+                         * have set something else (eg exit_request or
+                         * interrupt_request) which we will handle
+                         * next time around the loop.
+                         */
+                        tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
+                        next_tb = 0;
+                        break;
+                    case TB_EXIT_ICOUNT_EXPIRED:
+                    {
                         /* Instruction counter expired.  */
                         int insns_left;
                         tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
@@ -632,6 +651,10 @@  int cpu_exec(CPUArchState *env)
                             next_tb = 0;
                             cpu_loop_exit(env);
                         }
+                        break;
+                    }
+                    default:
+                        break;
                     }
                 }
                 cpu->current_tb = NULL;
diff --git a/exec.c b/exec.c
index a41bcb8..46a2830 100644
--- a/exec.c
+++ b/exec.c
@@ -495,7 +495,7 @@  void cpu_exit(CPUArchState *env)
     CPUState *cpu = ENV_GET_CPU(env);
 
     cpu->exit_request = 1;
-    cpu_unlink_tb(cpu);
+    cpu->tcg_exit_req = 1;
 }
 
 void cpu_abort(CPUArchState *env, const char *fmt, ...)
diff --git a/include/exec/gen-icount.h b/include/exec/gen-icount.h
index c858a73..384153b 100644
--- a/include/exec/gen-icount.h
+++ b/include/exec/gen-icount.h
@@ -7,10 +7,19 @@ 
 
 static TCGArg *icount_arg;
 static int icount_label;
+static int exitreq_label;
 
 static inline void gen_icount_start(void)
 {
     TCGv_i32 count;
+    TCGv_i32 flag;
+
+    exitreq_label = gen_new_label();
+    flag = tcg_temp_local_new_i32();
+    tcg_gen_ld_i32(flag, cpu_env,
+                   offsetof(CPUState, tcg_exit_req) - ENV_OFFSET);
+    tcg_gen_brcondi_i32(TCG_COND_NE, flag, 0, exitreq_label);
+    tcg_temp_free_i32(flag);
 
     if (!use_icount)
         return;
@@ -29,6 +38,9 @@  static inline void gen_icount_start(void)
 
 static void gen_icount_end(TranslationBlock *tb, int num_insns)
 {
+    gen_set_label(exitreq_label);
+    tcg_gen_exit_tb((tcg_target_long)tb + TB_EXIT_REQUESTED);
+
     if (use_icount) {
         *icount_arg = num_insns;
         gen_set_label(icount_label);
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index ee1a7c8..ab2657c 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -71,6 +71,8 @@  struct kvm_run;
  * @created: Indicates whether the CPU thread has been successfully created.
  * @stop: Indicates a pending stop request.
  * @stopped: Indicates the CPU has been artificially stopped.
+ * @tcg_exit_req: Set to force TCG to stop executing linked TBs for this
+ *           CPU and return to its top level loop.
  * @env_ptr: Pointer to subclass-specific CPUArchState field.
  * @current_tb: Currently executing TB.
  * @kvm_fd: vCPU file descriptor for KVM.
@@ -100,6 +102,7 @@  struct CPUState {
     bool stop;
     bool stopped;
     volatile sig_atomic_t exit_request;
+    volatile sig_atomic_t tcg_exit_req;
 
     void *env_ptr; /* CPUArchState */
     struct TranslationBlock *current_tb;
diff --git a/tcg/tcg.h b/tcg/tcg.h
index 2ebde07..90375c0 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -695,6 +695,10 @@  TCGv_i64 tcg_const_local_i64(int64_t val);
  *        would hit zero midway through it. In this case the next-TB pointer
  *        returned is the TB we were about to execute, and the caller must
  *        arrange to execute the remaining count of instructions.
+ *  3:    we stopped because the CPU's exit_request flag was set
+ *        (usually meaning that there is an interrupt that needs to be
+ *        handled). The next-TB pointer returned is the TB we were
+ *        about to execute when we noticed the pending exit request.
  *
  * If the bottom two bits indicate an exit-via-index then the CPU
  * state is correctly synchronised and ready for execution of the next
@@ -711,6 +715,7 @@  TCGv_i64 tcg_const_local_i64(int64_t val);
 #define TB_EXIT_IDX0 0
 #define TB_EXIT_IDX1 1
 #define TB_EXIT_ICOUNT_EXPIRED 2
+#define TB_EXIT_REQUESTED 3
 
 #if !defined(tcg_qemu_tb_exec)
 # define tcg_qemu_tb_exec(env, tb_ptr) \
diff --git a/translate-all.c b/translate-all.c
index b50fb89..9741d96 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -1475,7 +1475,7 @@  static void tcg_handle_interrupt(CPUArchState *env, int mask)
             cpu_abort(env, "Raised interrupt while not in I/O function");
         }
     } else {
-        cpu_unlink_tb(cpu);
+        cpu->tcg_exit_req = 1;
     }
 }
 
@@ -1626,7 +1626,7 @@  void cpu_interrupt(CPUArchState *env, int mask)
     CPUState *cpu = ENV_GET_CPU(env);
 
     env->interrupt_request |= mask;
-    cpu_unlink_tb(cpu);
+    cpu->tcg_exit_req = 1;
 }
 
 /*