Path: chuka.playstation.co.uk!news
From: "Craig Graham" <c_graham@hinge.mistral.co.uk>
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: GsLinkObject4 prototype error?
Date: 11 Aug 1998 16:17:41 GMT
Organization: PlayStation Net Yaroze (SCEE)
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Message-ID: <01bdc542$ea168620$230b0a0a@Angela1.intelligent-group.com>
References: <35CF88D3.4762@manc.u-net.com> <35CFA154.5EAB@manc.u-net.com> <35D03B22.5D50@manc.u-net.com> <35D05070.348AE2E@scee.sony.co.uk>
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James Russell <James_Russell@scee.sony.co.uk> wrote in article
<35D05070.348AE2E@scee.sony.co.uk>...
> James Shaughnessy wrote:
> > 
> > Turns out that passsing a u_long to GsLinkObject4 compiles fine
> > but crashes the program.
> 
> It shouldn't. GsLinkObject4 definitely needs a u_long, but internally
converts it to a u_long*.
> Instead of changing libps.h, it might be an idea to cast it properly:
> 
> u_long *memaddress = (u_long *)0x80091234;
> GsLinkObject4((u_long)(memaddress + 3), ....

Don't do that. What was happening is:

	GsLinkObject4((u_long*)memaddress + 3, ..)

cast's memaddr to a u_long*, then adds sizeof(u_long)*3 to it (check your
pointer addition semantics),
so you get the cast warning in the compiler, but it does work. Actual value
passed will be

	memaddr+sizeof(u_long)*3==&memaddress[3]==valid address

Doing what James suggests will indeed cause a crash as you then get the
actual value passed as:
	
	memaddr+3==an odd address==a crash like it says below.

> Because of your change to libps.h, the compiler will think that it is
passing a pointer instead of
> an integer. I can't think of any reason why, but it might just change the
code output by the
> compiler. (Actually, I checked - with my compiler, it doesn't, but GNU
might). It's more likely that
> you've done something like added 3 to a u_long, which will create an
unaligned address, crashing the
> system.

To ditch all the errors use:

	GsLinkObject4((u_long)memaddress + (u_long)(sizeof(u_long)*3),...)
or
	GsLinkObject4((u_long)((u_long*)memaddress + 3),...)

> Cheers,
> 
> James

Craig.