[PATCH v2 1/3] icount: preserve cflags when custom tb is about to execute

[Pavel Dovgalyuk]

When debugging with the watchpoints, qemu may need to create
TB with single instruction. This is achieved by setting cpu->cflags_next_tb.
But when this block is about to execute, it may be interrupted by another
thread. In this case cflags will be lost and next executed TB will not
be the special one.
This patch checks TB exit reason and restores cflags_next_tb to allow
finding the interrupted block.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
---
 accel/tcg/cpu-exec.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 2d14d02f6c..df12452b8f 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -846,6 +846,16 @@ static inline void cpu_loop_exec_tb(CPUState *cpu, 
TranslationBlock *tb,
          * cpu_handle_interrupt.  cpu_handle_interrupt will also
          * clear cpu->icount_decr.u16.high.
          */
+        if (cpu->cflags_next_tb == -1
+            && (!use_icount || !(tb->cflags & CF_USE_ICOUNT)
+                || cpu_neg(cpu)->icount_decr.u16.low >= tb->icount)) {
+            /*
+             * icount is disabled or there are enough instructions
+             * in the budget, do not retranslate this block with
+             * different parameters.
+             */
+            cpu->cflags_next_tb = tb->cflags;
+        }
         return;
     }