Re: [elysium-developers] PCT

[Adam L. <ag...@li...>]

On Sun, Feb 20, 2000 at 12:54:53PM +0100, Kasper Verdich Lund wrote:
> > Well I'm stuck again ;(
>=20
> Okay - let's see...

BTW: Im Nebulae on us.chatjunkies.org, #linux

> What's your strategy? Do you intend to let the called process return?
> When I did the IRQ handling stuff I made a mistake that produced strange
> results. I ran the IRQ handling process with _process_run() which
> changes the address space (by changing CR3), but on return I didn't
> change back.=20

Process 1 wants to jump to process 2:
It saves state so prolog can restore state=20
It sets up the pid in %eax
It sets a value in %ebx
int $0x47
kernel jumps to the PCT entry in process 2
process 2 does what it wants
at somepoint process 1 prolog is called and everything continues

> > All the movl    $xx,%ecx are debugging
> > t2 crashes with ECX=3D59 everytime (and I've put delay loops in to chec=
k it isn't
> > a timing thing).

Doh! The ECX came from prolog when it popal's. In sys_pct I push (in order):
pushl  0x10000950
pusha
pushf

Now prolog pops the flags and registers ok, but the ret seems to jump to
0xc35831eb

> I'm really worried about the SS =3D 0x00100023 - could you send me the
> code? I want to investigate :-)

SS is 16bit. Thus that 1 can't be there. It must be from the debug code that
prints the value

> =20
> > It must be that pushal crashing I think (because if it ever finished EC=
X would
> > change). But how does EIP go so wonkey?
>=20
> It's easy to mess up EIP - if you fail to maintain the stack properly a
> single 'ret' instruction will certainly do something like that.

But popal seems to restore all the registers to the correct values in prolo=
g,
which makes me think the stack is OK

> BTW: Let's make a debug system call (interrupt 3 would do fine) and let
> that dump some basic CPU information. That would be useful instead of
> the movl $xx,%ecx stuff :-)

It wouldn't have helped, but it sounds a good idea. Maybe we it could set t=
he
single-step flag (that would have been usful), if the kernel dumps state on
every instruction. Also maybe the kernel could write it to a serial port...

AGL

--=20
Smoking is one of the leading causes of statistics.