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Re: [Qemu-devel] Signal management in qemu-user

From: Alex Barcelo
Subject: Re: [Qemu-devel] Signal management in qemu-user
Date: Thu, 24 May 2012 09:19:34 +0200

On Thu, May 24, 2012 at 1:04 AM, Peter Maydell <address@hidden> wrote:
> On 23 May 2012 23:38, Alex Barcelo <address@hidden> wrote:
>> This *always* goes wrong without calling the signal handler
> I haven't looked too closely, but I suspect we're just not
> paying any attention to whether memory does or doesn't have
> the PROT_EXEC permission when we translate code from it.

Ok, makes sense.

> This is the kind of corner case that the linux-user code is
> often not very good at, because not many guest programs play
> this sort of game.

I see. But, does qemu-system play this sort of game? I haven't been
able to find this sort of protect-catch-unprotect for execution, and
my goal is to run qemu-system on top of qemu-user. The self-modifying
code is done through the write protection of memory pages, but I can't
see which would be the root problem. It seems that self-modifying code
is done in two levels, in qemu-user and in qemu-system, but this
should not be a problem... once the signal mask is correctly managed
by usermode. Am I right?

I plan to bugfix the usermode masking problem as best as I can, but
first I wanted to make sure that this will bring me closer to the

Thanks a lot for your time and patience

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