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Re: [Qemu-devel] Regarding TB retranslation code.

From: Peter Maydell
Subject: Re: [Qemu-devel] Regarding TB retranslation code.
Date: Tue, 15 Mar 2016 13:27:29 +0000

On 15 March 2016 at 13:17, Venkatesh N <address@hidden> wrote:
> Thanks Alex.
> While executing the host instruction(s) for the guest instruction,
> when a callq to c helper routine is made,  will every CALLQ will be
> treated as End of TB. If so, what happens to TB optimizations.

No, a call to a helper function does not automatically end the TB.
A helper function can be marked with flags to indicate whether it
has side effects or reads or writes globals (see the "Helpers" section
in tcg/README) -- this then affects whether the optimization pass
and register allocator write TCG values back to memory before the
call or not. (A helper which can trigger an exception counts as
having a side effect, so guest register values are written back
to their canonical locations in the CPU state struct before the

-- PMM

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