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

[Arnabjyoti Kalita]

Hi Peter,

Thanks for highlighting this.

Regards,
Arnabjyoti Kalita

On Wed, May 16, 2018 at 9:14 AM, Peter Maydell <address@hidden>
wrote:

> 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
>