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Re: [Qemu-devel] interrupt handling in qemu

From: Avi Kivity
Subject: Re: [Qemu-devel] interrupt handling in qemu
Date: Wed, 28 Dec 2011 14:04:21 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111115 Thunderbird/8.0

On 12/28/2011 01:40 PM, Peter Maydell wrote:
> On 28 December 2011 10:42, Avi Kivity <address@hidden> wrote:
> > It's possible to check for an interrupt before every instruction,
> > without any overhead:
> >
> > - when a signal arrives, check the instruction pointer. If it points
> > outside tcg code, set a flag and return.
> > - consult a table indexed by the instruction pointer, that gives the
> > number of bytes to the next guest instruction boundary
> > - if nonzero, set a breakpoint at that boundary, and resume
> > - remove the breakpoint (if set)
> > - adjust the TB to return on the current instruction pointer
> > - return
> This assumes you have hardware breakpoints on your host, so
> it's not portable.

You could also use software breakpoints.  Or just temporarily replace
the host instruction on the next guest instruction boundary with a return.

> (You also need to add a check-and-handle-flag for every return
> from a helper function to TCG code, 

ah yes - didn't consider that.

you could put all helper in their own section, an do something around
that - but that assumes no callouts from helpers to the standard library.

> and of course you need to
> actually create the instruction-boundary table. 

This should be well amortized.

> These are both
> overheads.)

error compiling committee.c: too many arguments to function

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