Re: init receiving SIGILL on XEN3_DOM0/amd64

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

Manuel Bouyer wrote:
> On Sun, May 18, 2008 at 02:32:37PM +0200, Manuel Bouyer wrote:
> > On Sun, May 18, 2008 at 01:43:04PM +0200, Christoph Egger wrote:
> > > > When the CPU sends an illegal intruction trap, I guess.
> > > In that case, I have a wild guess:
> > > sysenter is an illegal opcode on amd64. The difference is, AMD CPUs 
> > > throw an exception, Intel CPUs don't.
> > > Is sysenter used somewhere?
> > I don't think it should be for amd64 binaries.
> > i386 binaries may, but only if I686_LIBC is defined. Othewrise int $0x80
> > is used.
>
> OK, I've been seeing this occasionally now on an Intel CPU. A dom0 kernel will
> fail to start init in this way once in a while. But hitting ^A^A^AR on the
> serial console cause the system to reboot, and the next boot is usually
> successfull without changing anything in kernel or boot options.
>
> The intermittent aspect makes it hard to debug, and also confuses me a bit
> about what the cause could be.

I see this, too on AMD CPU. I tracked this down to when start_init() 
returns to lwp_trampoline which in turn returns to Xosyscall.
Xosyscall wants to send SIG 4 to pid 1 (no idea why)
and calls trap for this.
In trap a page fault happens which in turn leads into an
endless loop of traps into ddb.

Christoph