tcg: Clean up from 'next_tb'

The value returned from tcg_qemu_tb_exec() is the value passed to the
corresponding tcg_gen_exit_tb() at translation time of the last TB
attempted to execute. It is a little confusing to store it in a variable
named 'next_tb'. In fact, it is a combination of 4-byte aligned pointer
and additional information in its two least significant bits. Break it
down right away into two variables named 'last_tb' and 'tb_exit' which
are a pointer to the last TB attempted to execute and the TB exit
reason, correspondingly. This simplifies the code and improves its
readability.

Correct a misleading documentation comment for tcg_qemu_tb_exec() and
fix logging in cpu_tb_exec(). Also rename a misleading 'next_tb' in
another couple of places.

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>

1 files changed, 10 insertions, 9 deletions

diff --git a/tcg/tcg.h b/tcg/tcg.h
index 0fceef5333..a013d77a33 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -925,7 +925,7 @@ static inline unsigned get_mmuidx(TCGMemOpIdx oi)
 
 /**
  * tcg_qemu_tb_exec:
- * @env: CPUArchState * for the CPU
+ * @env: pointer to CPUArchState for the CPU
  * @tb_ptr: address of generated code for the TB to execute
  *
  * Start executing code from a given translation block.
@@ -936,30 +936,31 @@ static inline unsigned get_mmuidx(TCGMemOpIdx oi)
  * which has not yet been directly linked, or an asynchronous
  * event such as an interrupt needs handling.
  *
- * The return value is a pointer to the next TB to execute
- * (if known; otherwise zero). This pointer is assumed to be
- * 4-aligned, and the bottom two bits are used to return further
- * information:
+ * Return: The return value is the value passed to the corresponding
+ * tcg_gen_exit_tb() at translation time of the last TB attempted to execute.
+ * The value is either zero or a 4-byte aligned pointer to that TB combined
+ * with additional information in its two least significant bits. The
+ * additional information is encoded as follows:
  *  0, 1: the link between this TB and the next is via the specified
  *        TB index (0 or 1). That is, we left the TB via (the equivalent
  *        of) "goto_tb <index>". The main loop uses this to determine
  *        how to link the TB just executed to the next.
  *  2:    we are using instruction counting code generation, and we
  *        did not start executing this TB because the instruction counter
- *        would hit zero midway through it. In this case the next-TB pointer
+ *        would hit zero midway through it. In this case the pointer
  *        returned is the TB we were about to execute, and the caller must
  *        arrange to execute the remaining count of instructions.
  *  3:    we stopped because the CPU's exit_request flag was set
  *        (usually meaning that there is an interrupt that needs to be
- *        handled). The next-TB pointer returned is the TB we were
- *        about to execute when we noticed the pending exit request.
+ *        handled). The pointer returned is the TB we were about to execute
+ *        when we noticed the pending exit request.
  *
  * If the bottom two bits indicate an exit-via-index then the CPU
  * state is correctly synchronised and ready for execution of the next
  * TB (and in particular the guest PC is the address to execute next).
  * Otherwise, we gave up on execution of this TB before it started, and
  * the caller must fix up the CPU state by calling the CPU's
- * synchronize_from_tb() method with the next-TB pointer we return (falling
+ * synchronize_from_tb() method with the TB pointer we return (falling
  * back to calling the CPU's set_pc method with tb->pb if no
  * synchronize_from_tb() method exists).
  *