accel/tcg: Introduce translator_use_goto_tb

Add a generic version of the common use_goto_tb test.

Various targets avoid the page crossing test for CONFIG_USER_ONLY,
but that is wrong: mmap and mprotect can change page permissions.

Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/translator.c

@@ -31,6 +31,17 @@ void translator_loop_temp_check(DisasContextBase *db)
     }
 }
 
+bool translator_use_goto_tb(DisasContextBase *db, target_ulong dest)
+{
+    /* Suppress goto_tb in the case of single-steping.  */
+    if (db->singlestep_enabled || singlestep) {
+        return false;
+    }
+
+    /* Check for the dest on the same page as the start of the TB.  */
+    return ((db->pc_first ^ dest) & TARGET_PAGE_MASK) == 0;
+}
+
 void translator_loop(const TranslatorOps *ops, DisasContextBase *db,
                      CPUState *cpu, TranslationBlock *tb, int max_insns)
 {

include/exec/translator.h

@@ -145,6 +145,16 @@ void translator_loop(const TranslatorOps *ops, DisasContextBase *db,
 
 void translator_loop_temp_check(DisasContextBase *db);
 
+/**
+ * translator_use_goto_tb
+ * @db: Disassembly context
+ * @dest: target pc of the goto
+ *
+ * Return true if goto_tb is allowed between the current TB
+ * and the destination PC.
+ */
+bool translator_use_goto_tb(DisasContextBase *db, target_ulong dest);
+
 /*
  * Translator Load Functions
  *