Re: [Qemu-discuss] Understanding the return value of the function tcg_qemu_tb_exec()

[Peter Maydell]

On 15 May 2018 at 22:09, Arnabjyoti Kalita <address@hidden> wrote:
> I was trying to understand what the function tcg_qemu_tb_exec() returns. I
> can understand that the last two bits of the return value contain the exit
> status of the translation block that just got executed. However I cannot
> understand what the remaining bits in the value point to. I find it hard to
> understand what it returns from the source code.
>
> Basically, I am finding it hard to determine if this function returns the
> current TB that was executed or that it returns the next TB that is to be
> executed.

That depends on the value in the bottom two bits. If the bottom two
bits are 2 or 3, then the pointer part is the TB we were about to
execute but abandoned execution of. If the bottom two bits are 0 or 1,
then the return value is whatever we passed to tcg_gen_exit_tb()
when we were generating the code for the exit path for the TB we
just executed. The pointer part will either be 0, or the address
of that just-executed TB. (We use this to try to link the
just-executed TB to the next one, so 0 means "don't try to link".)

thanks
-- PMM