Date: Tue, 10 Sep 2002 10:35:24 -0400 (EDT) From: Andrew Gallatin <gallatin@cs.duke.edu> To: ticso@cicely.de Cc: Joe Marcus Clarke <marcus@marcuscom.com>, alpha@FreeBSD.ORG Subject: Re: getting closer (was Re: mozilla failure on 4.6.2) Message-ID: <15742.812.130498.758611@grasshopper.cs.duke.edu> In-Reply-To: <20020910140414.GC5057@cicely5.cicely.de> References: <1031329151.342.9.camel@gyros.marcuscom.com> <20020906194732.GA2244@dragon.nuxi.com> <15737.2550.488154.4401@grasshopper.cs.duke.edu> <20020907000825.GA4091@dragon.nuxi.com> <15739.43883.152090.936327@grasshopper.cs.duke.edu> <15741.2822.526047.253409@grasshopper.cs.duke.edu> <1031605410.351.90.camel@gyros.marcuscom.com> <15741.17468.701009.998323@grasshopper.cs.duke.edu> <1031635953.342.133.camel@gyros.marcuscom.com> <15741.61382.872535.426732@grasshopper.cs.duke.edu> <20020910140414.GC5057@cicely5.cicely.de>
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Bernd Walter writes:
> On Tue, Sep 10, 2002 at 09:12:38AM -0400, Andrew Gallatin wrote:
> >
> > Joe Marcus Clarke writes:
> > > Add 8 to the stack pointer ("this", right), and store it in $16.
> >
> > I wish it were that simple :-(
> >
> > The problem seems to be that the application code is passing the
> > "wrong" value in and somehow the c++ calling standard corrects it, and
> > we must correct it too:
> >
> > impl == 0x12001c080
> > foo == 0x12001c080
> > bar == 0x12001c088
>
> I have no idea how the class declaration for you example looks like.
http://lxr.mozilla.org/seamonkey/source/xpcom/reflect/xptcall/tests/TestXPTCInvoke.cpp
> Possible because I don't know the mozilla code you are talking about.
> What is the difference in direct and invoke calling?
"direct" is a normal c++ call: bar->BarMethod1(1);
"invoke" means the mozilla xptinvoke shims:
var[0].val.i32 = 1;
var[0].type = nsXPTType::T_I32;
var[0].flags = 0;
XPTC_InvokeByIndex(bar, 3, 1, var);
They are described at:
http://www.mozilla.org/scriptable/xptcall-faq.html
> Lets asume foo is a virtual function of class x which is based on
> class y defining the virtual function bar.
> >From what I know about C++ (which might be outdated) we have the
> following situation when using an object of class x.
> Call of function bar means the caller knows the offset to the function
> pointer, because it's using a pointer of type x.
> The function bar expects a this pointer of type y so it gets the
> this pointer of the embedded y object which may be numericaly different.
>
> Now asume class x reimplement the virtual function bar.
> The newly bar function has to share the calling conventions that were
> declared by class y.
> If we call function bar using a type y pointer we submit a this pointer
> of type y.
> But the function is designed to have a this pointer of type x.
> Now the function must recalculate the supplied y pointer into an x
> pointer.
> If we call funtcion bar using a type x pointer we still have to convert
> the x pointer into an y pointer because the function still expects an y
> pointer.
I assume this is all done "behind the scenes" by the compiler?
Is there a convention for where the conversions are passed?
Since you know quite a bit about c++, and because you know alpha asm,
I'd _really_ like your help ;) Do you have an alpha running
-stable? Or are you all -current these days?
Thanks,
Drew
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