tcg: Diagnose referenced labels that have not been emitted

Currently, a jump to a label that is not defined anywhere will
be emitted not be relocated.  This results in a jump to a random
jump target.  With tcg debugging, print a diagnostic to the -d op
file and abort.

This could help debug or detect errors like
c2d9644e6d ("target/arm: Fix crash on conditional instruction in an IT block")

Reported-by: Roman Kapl <code@rkapl.cz>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/tcg/tcg.c b/tcg/tcg.c
index 20a5d8f..9b2bf7f 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -305,6 +305,9 @@ TCGLabel *gen_new_label(void)
     *l = (TCGLabel){
         .id = s->nb_labels++
     };
+#ifdef CONFIG_DEBUG_TCG
+    QSIMPLEQ_INSERT_TAIL(&s->labels, l, next);
+#endif
 
     return l;
 }
@@ -1092,6 +1095,9 @@ void tcg_func_start(TCGContext *s)
 
     QTAILQ_INIT(&s->ops);
     QTAILQ_INIT(&s->free_ops);
+#ifdef CONFIG_DEBUG_TCG
+    QSIMPLEQ_INIT(&s->labels);
+#endif
 }
 
 static inline TCGTemp *tcg_temp_alloc(TCGContext *s)
@@ -3841,6 +3847,23 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb)
     }
 #endif
 
+#ifdef CONFIG_DEBUG_TCG
+    /* Ensure all labels referenced have been emitted.  */
+    {
+        TCGLabel *l;
+        bool error = false;
+
+        QSIMPLEQ_FOREACH(l, &s->labels, next) {
+            if (unlikely(!l->present) && l->refs) {
+                qemu_log_mask(CPU_LOG_TB_OP,
+                              "$L%d referenced but not present.\n", l->id);
+                error = true;
+            }
+        }
+        assert(!error);
+    }
+#endif
+
 #ifdef CONFIG_PROFILER
     atomic_set(&prof->opt_time, prof->opt_time - profile_getclock());
 #endif