L4-Linux worked on 486!

[edmundo at rano.demon.co.uk]

> Just I could boot L4-Linux and execute "ls" etc on 486,
> without rebooting.

L4-Linux is running quite nicely for me now, but I can still crash it
by doing cksum /usr/bin/* over CVS. It dies after saying "irq still
active". (To get that message I'm using the patch that Michael Hohmuth
posted to the list on July 25.)

I think I may have found a bug in the SANITY code in
linux22/arch/l4-i386/kernel/irq.c, by the way. See below.

> After several trying of remote debug, I think "kernel"-debugger
> is not so much powerful to detect how L4-Linux "server" breaks down.
> It's not easy for me to understand what happens in the server 
> program from the system calls.

What I have been doing is telling GDB "symbol-file .../vmlinux" to
inspect what's happening in Linux, then "symbol-file .../kernel.image"
to go back to inspecting Fiasco. There's probably some way of defining
macros to make that switching a bit easier. I don't know if GDB could
use both sets of symbols at the same time.

It took me ages to discover how to find out the current location
(program counter) of a given thread. (If you've got thread_t *t, the
thread is running at *(void *)((char *)t+0x7ec), IIRC.)

If there's one good thing to come out of my playing around with
L4-Linux, I've learnt a bit about GDB ...

(This is a bit off topic, but does anyone know a better solution to
this one? I tell GDB "p spong" and get a value that is totally wrong.
This is because the variable has been optimised into a register. So to
find out its value I use "disassemble" and "info registers". Is there
a quicker way?)

Edmund



This is what I did to linux22/arch/l4-i386/kernel/irq.c:

In timer_irq_thread(), I moved

#ifdef SANITY
      irqs_in_progress &= ~(1 << TIMER_IRQ);
#endif

from its present position just before the call to
l4_i386_ipc_receive() to just before the call to
execute_bottom_halves(). This got rid of the "irq active" messages
which I think are spurious.

Sorry for the lack of patch but I've rather lost control of the
versions of that file ...