[v3,4/6] target/arm/translate: ensure gen_goto_tb sets exit flags

Message ID 20170711175937.23140-5-alex.bennee@linaro.org
State New
Headers show
Series
  • arm: fixes for eret, isb and DISAS_UPDATE handling
Related show

Commit Message

Alex Bennée July 11, 2017, 5:59 p.m.
As the gen_goto_tb function can do both static and dynamic jumps it
should also set the is_jmp field. This matches the behaviour of the
a64 code.

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

---
 target/arm/translate.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

-- 
2.13.0

Comments

Richard Henderson July 11, 2017, 6:16 p.m. | #1
On 07/11/2017 07:59 AM, Alex Bennée wrote:
>       if (use_goto_tb(s, dest)) {

>           tcg_gen_goto_tb(n);

>           gen_set_pc_im(s, dest);

>           tcg_gen_exit_tb((uintptr_t)s->tb + n);

> +        s->is_jmp = DISAS_TB_JUMP;

>       } else {

>           gen_set_pc_im(s, dest);

>           gen_goto_ptr();

> +        s->is_jmp = DISAS_JUMP;

>       }


I think DISAS_TB_JUMP is appropriate for both cases.  When not using goto_tb, 
the jump is still static and we still chain to the next TB via goto_ptr.

Otherwise,

Reviewed-by: Richard Henderson <rth@twiddle.net>



r~
Alex Bennée July 11, 2017, 7:20 p.m. | #2
Richard Henderson <rth@twiddle.net> writes:

> On 07/11/2017 07:59 AM, Alex Bennée wrote:

>>       if (use_goto_tb(s, dest)) {

>>           tcg_gen_goto_tb(n);

>>           gen_set_pc_im(s, dest);

>>           tcg_gen_exit_tb((uintptr_t)s->tb + n);

>> +        s->is_jmp = DISAS_TB_JUMP;

>>       } else {

>>           gen_set_pc_im(s, dest);

>>           gen_goto_ptr();

>> +        s->is_jmp = DISAS_JUMP;

>>       }

>

> I think DISAS_TB_JUMP is appropriate for both cases.  When not using

> goto_tb, the jump is still static and we still chain to the next TB

> via goto_ptr.


OK - I guess we need to nail down what the essential difference is
between the two. I understood DISAS_TB_JUMP as a static known PC which
can be patched in the generated code because we know the two addresses
are in the same page - whereas DISAS_JUMP is a "computed" jump although
in this case the PC is already known.

Does making a distinction between computed and non-computer inter-page
jumps make any sense anyway?

>

> Otherwise,

>

> Reviewed-by: Richard Henderson <rth@twiddle.net>

>

>

> r~



--
Alex Bennée
Richard Henderson July 11, 2017, 9:08 p.m. | #3
On 07/11/2017 09:20 AM, Alex Bennée wrote:
> 

> Richard Henderson <rth@twiddle.net> writes:

> 

>> On 07/11/2017 07:59 AM, Alex Bennée wrote:

>>>        if (use_goto_tb(s, dest)) {

>>>            tcg_gen_goto_tb(n);

>>>            gen_set_pc_im(s, dest);

>>>            tcg_gen_exit_tb((uintptr_t)s->tb + n);

>>> +        s->is_jmp = DISAS_TB_JUMP;

>>>        } else {

>>>            gen_set_pc_im(s, dest);

>>>            gen_goto_ptr();

>>> +        s->is_jmp = DISAS_JUMP;

>>>        }

>>

>> I think DISAS_TB_JUMP is appropriate for both cases.  When not using

>> goto_tb, the jump is still static and we still chain to the next TB

>> via goto_ptr.

> 

> OK - I guess we need to nail down what the essential difference is

> between the two. I understood DISAS_TB_JUMP as a static known PC which

> can be patched in the generated code because we know the two addresses

> are in the same page - whereas DISAS_JUMP is a "computed" jump although

> in this case the PC is already known.

> 

> Does making a distinction between computed and non-computer inter-page

> jumps make any sense anyway?


*shrug* probably not.

Honestly, the only thing that's really interesting here is that is_jmp indicate 
that we have already exited the TB and that all following code is dead.

As a response to one of Lluis' threads, I suggested that the generic term for 
this be DISAS_NORETURN.  Which also covers exiting the TB via calling a helper 
that does not return, e.g. throwing an illegal opcode exception, aka DISAS_EXC 
in the current target/arm sources.


r~

Patch hide | download patch | download mbox

diff --git a/target/arm/translate.c b/target/arm/translate.c
index 5f2cea8641..82341ee709 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -4158,15 +4158,20 @@  static void gen_goto_ptr(void)
     tcg_temp_free(addr);
 }
 
+/* This will end the TB but doesn't guarantee we'll return to
+ * cpu_loop_exec. Any live exit_requests will be processed as we
+ * enter the next TB. */
 static void gen_goto_tb(DisasContext *s, int n, target_ulong dest)
 {
     if (use_goto_tb(s, dest)) {
         tcg_gen_goto_tb(n);
         gen_set_pc_im(s, dest);
         tcg_gen_exit_tb((uintptr_t)s->tb + n);
+        s->is_jmp = DISAS_TB_JUMP;
     } else {
         gen_set_pc_im(s, dest);
         gen_goto_ptr();
+        s->is_jmp = DISAS_JUMP;
     }
 }
 
@@ -4179,7 +4184,6 @@  static inline void gen_jmp (DisasContext *s, uint32_t dest)
         gen_bx_im(s, dest);
     } else {
         gen_goto_tb(s, 0, dest);
-        s->is_jmp = DISAS_TB_JUMP;
     }
 }