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Re: [Qemu-devel] [PATCH] exec.c: simplify the breakpoint invalidation lo


From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH] exec.c: simplify the breakpoint invalidation logic
Date: Tue, 6 Dec 2016 16:09:26 +0000

On 6 December 2016 at 15:14, Alex Bennée <address@hidden> wrote:
> Peter Maydell <address@hidden> writes:
>> I think this is the wrong direction. We only need to invalidate
>> the TBs for the specific location the breakpoint is at.
>> Even if we for the moment want to apply a big hammer of doing
>> a full tb flush on breakpoint to fix this issue for this release,
>> we shouldn't drop the indirection through breakpoint_invalidate(),
>> because then we can't go back to invalidating just the parts we need
>> easily later.
>
> Why would we? It's not like fresh code generation is particularly slow,
> especially in a debugging situation when you've just stopped the
> machine.

Because a wholescale tb_flush() is a "this is probably wrong"
flag, and a great way to hide bugs. It also makes the gdbstub
more invasive than it strictly has to be.

We have less than 10 calls to tb_flush() in the whole system
and I think they could all use examination to see whether
they're really correct.

thanks
-- PMM



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