cpu-exec: Add "nochain" debug flag

Respect it to avoid linking TBs together.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>

cpu-exec.c

@@ -477,7 +477,8 @@ int cpu_exec(CPUState *cpu)
                 /* 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) {
+                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);
                 }

include/qemu/log.h

@@ -41,6 +41,7 @@ static inline bool qemu_log_enabled(void)
 #define LOG_UNIMP          (1 << 10)
 #define LOG_GUEST_ERROR    (1 << 11)
 #define CPU_LOG_MMU        (1 << 12)
+#define CPU_LOG_TB_NOCHAIN (1 << 13)
 
 /* Returns true if a bit is set in the current loglevel mask
  */

qemu-log.c

@@ -119,6 +119,9 @@ 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",
+      "do not chain compiled TBs so that \"exec\" and \"cpu\" show\n"
+      "complete traces" },
     { 0, NULL, NULL },
 };