[Qemu-devel] [PATCH v2 7/7] qemu-log: add nochain option to disable TB chaining

["Alex Bennée" <alex.bennee@linaro.org>]

The current exec and cpu flags only show information when we enter a
TranslationBlock. The blocks will then chain together until there is a
reason to exit which can make things harder to follow. This new option
disables the chaining for debugging purposes.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

diff --git a/cpu-exec.c b/cpu-exec.c
index abe02b7..c20349c 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -620,8 +620,10 @@ int cpu_exec(CPUArchState *env)
                 }
                 /* see if we can patch the calling TB. When the TB
                    spans two pages, we cannot safely do a direct
-                   jump. */
-                if (next_tb != 0 && tb->page_addr[1] == -1) {
+                   jump. It can also complicate tracing so disable if
+                   asked (but be aware this can change behaviour). */
+                if (next_tb != 0 && tb->page_addr[1] == -1 &&
+                    !qemu_loglevel_mask (CPU_LOG_TB_NOCHAIN)) {
                     tb_add_jump((TranslationBlock *)(next_tb & ~TB_EXIT_MASK),
                                 next_tb & TB_EXIT_MASK, tb);
                 }
diff --git a/include/qemu/log.h b/include/qemu/log.h
index f6cef9e..82902b0 100644
--- a/include/qemu/log.h
+++ b/include/qemu/log.h
@@ -40,6 +40,7 @@ static inline bool qemu_log_enabled(void)
 #define CPU_LOG_RESET      (1 << 9)
 #define LOG_UNIMP          (1 << 10)
 #define LOG_GUEST_ERROR    (1 << 11)
+#define CPU_LOG_TB_NOCHAIN (1 << 12)
 
 /* Returns true if a bit is set in the current loglevel mask
  */
diff --git a/qemu-log.c b/qemu-log.c
index a54b332..dc78a93 100644
--- a/qemu-log.c
+++ b/qemu-log.c
@@ -175,6 +175,8 @@ const QEMULogItem qemu_log_items[] = {
     { LOG_GUEST_ERROR, "guest_errors",
       "log when the guest OS does something invalid (eg accessing a\n"
       "non-existent register)" },
+    { CPU_LOG_TB_NOCHAIN, "nochain",
+      "disable chaining of translation blocks (better tracing, but slower)" },
     { 0, NULL, NULL },
 };
 
-- 
1.9.1