[Qemu-devel] cpu_exit every time for a jump tb (containing only the "b" instruction)

[阮安邦 <anbang.ruan@gmail.com>]

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Hi, list

       I am currently profiling qemu-system-arm. I wrote a simple ARM
assembly only to add r0 infinitely:

 *   add_nums:
            add r0, r0, r1
            b add_nums*

       I forced a tb to contain only one instruction, and I got cpu_exit
every time the tb for "*b add_nums"* was executed. It exited the cpu_exec
loop every time, and then reentered it and executed it without cpu_exit.

       Following are the executing sequences. I dumped the "in_asm" for a tb
every time it was executed. And wrapped the *tcg_qemu_tb_exec*() with
qemu_log().


*IN:
0x8001000c:  b    0x80010008

before tcg_qemu_tb_exec
cpu_exit
after tcg_qemu_tb_exec*


*IN:
0x8001000c:  b    0x80010008

before tcg_qemu_tb_exec
after tcg_qemu_tb_exec

IN:
0x80010008:  add    r0, r0, r1

before tcg_qemu_tb_exec
after tcg_qemu_tb_exec


IN:
0x8001000c:  b    0x80010008

before tcg_qemu_tb_exec
cpu_exit
after tcg_qemu_tb_exec

*
      It seems like the cpu_exit was called when * tcg_qemu_tb_exec *was
executing. However,  * tcg_qemu_tb_exec* is only to execute the translated
native code (am i right?), how can it call the qemu func (cpu_exit)? Or it
is called by other func executing simultaneously with  * tcg_qemu_tb_exec*?*
* And why cpu_exit is called everytime, it really comsumes lots of ticks.~

      Any suggestions? Great thanks!


Regards,
Ryan

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