Re: [Qemu-devel] [PATCH] target-arm: Minimal implementation of performance counters

[Aurelien Jarno <aurelien@aurel32.net>]

On Mon, Apr 25, 2011 at 11:35:54PM +0100, Peter Maydell wrote:
> On 25 April 2011 23:31, Aurelien Jarno <aurelien@aurel32.net> wrote:
> > On Mon, Apr 25, 2011 at 10:59:52PM +0100, Peter Maydell wrote:
> >> On 25 April 2011 22:09, Aurelien Jarno <aurelien@aurel32.net> wrote:
> >> > Instead of having this complex test for all cp15 access, but only for
> >> > catching a few access to performance registers, wouldn't it make more
> >> > sense to have this test and an exception triggering directly in
> >> > helper.c?
> >>
> >> That was what my first design did, but in discussions on IRC
> >> with Paul Brook he basically said that you can't generate an
> >> exception in the helper routine, you have to either generate
> >> runtime code to do the test or throw away the TBs. Unfortunately
> >> I forget the exact rationale, so I've cc'd Paul to remind me :-)
> >
> > This is something strange, plenty of targets are raising exceptions from
> > helpers without any problem.
> 
> You'd at minimum need to move the cp15 helper functions to a different
> file, they're currently in helper.c which doesn't get compiled
> with access to the global 'env' register. But I got the impression
> there was something more significant than that.
> 

I agree, but it's something that has to be done sooner or later anyway.

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net