tcg: Add support for debugging leakage of temporaries

Add support (if CONFIG_DEBUG_TCG is defined) for debugging leakage
of temporary variables. Generally any temporaries created by
a target while it is translating an instruction should be freed
by the end of that instruction; otherwise carefully crafted
guest code could cause TCG to run out of temporaries and assert.
By calling tcg_check_temp_count() after each instruction we can
check that we are not leaking temporaries in this way.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 17 insertions, 0 deletions

diff --git a/tcg/tcg.h b/tcg/tcg.h
index e1afde26b4..3fab8d6c27 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -323,6 +323,10 @@ struct TCGContext {
     int64_t restore_count;
     int64_t restore_time;
 #endif
+
+#ifdef CONFIG_DEBUG_TCG
+    int temps_in_use;
+#endif
 };
 
 extern TCGContext tcg_ctx;
@@ -392,6 +396,19 @@ static inline TCGv_i64 tcg_temp_local_new_i64(void)
 void tcg_temp_free_i64(TCGv_i64 arg);
 char *tcg_get_arg_str_i64(TCGContext *s, char *buf, int buf_size, TCGv_i64 arg);
 
+#if defined(CONFIG_DEBUG_TCG)
+/* If you call tcg_clear_temp_count() at the start of a section of
+ * code which is not supposed to leak any TCG temporaries, then
+ * calling tcg_check_temp_count() at the end of the section will
+ * return 1 if the section did in fact leak a temporary.
+ */
+void tcg_clear_temp_count(void);
+int tcg_check_temp_count(void);
+#else
+#define tcg_clear_temp_count() do { } while (0)
+#define tcg_check_temp_count() 0
+#endif
+
 void tcg_dump_info(FILE *f, fprintf_function cpu_fprintf);
 
 #define TCG_CT_ALIAS  0x80