Re: Race condition in Mach/Hurd?

[Samuel Thibault]

Svante Signell, le Tue 10 May 2011 14:00:07 +0200, a écrit :
> On Tue, 2011-05-10 at 13:34 +0200, Samuel Thibault wrote:
> 
> > > 
> > > It's not so simple as you say: I have now found out where the
> > > mach_port_deallocate_debug variable is in gnumach-1.3.99-486-dbg (copied
> > > from boot and uncompressed). I have two alternatives:
> > > 
> > > 1) Write a one into that address without using the kernel debugger, how?
> > 
> > That's an option. Use objdump -d gnumach-1.3.99-486-dbg to determine the
> > file offset of the variable, and use a hex editor. It's really not the
> > simplest way.
> 
> Well objdump gave a lot of hits for mach_port_deallocate but
> mach_port_deallocate_debug was not found. And the addresses are
> different from the hex editor. Anyway using objdump -D I found it:
> 
> 002c10c0 <mach_port_deallocate_debug>:
>   2c10c0:       00 00                   add    %al,(%eax)

But that's not a file offset.  Actually I meant objdump -x, to get the
headers, which tell you know virtual addresses relate with file offsets.

> > > 2) Uncompress it at /boot
> > > Start the debugger with C-A-d. Does this work on an uncompressed image?
> > > w 002c10c0 1
> > > cont
> > 
> > There's a misunderstanding: w writes in the living kernel and has
> > immediate non-permanent effect, not in /boot.
> 
> Partly understood, does this command apply to the -dbg version of
> gnumach in the running kernel?

Yes. The non-dbg version doesn't have the debugger at all.

Samuel