Re: init receiving SIGILL on XEN3_DOM0/amd64

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

On Monday 26 May 2008 22:57:06 Christoph Egger wrote:
> 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.

start_init() returns to lwp_trampoline which in turn jmp into Xosyscall.

Xosyscall notices an AST is pending and calls trap. trap sends SIG 4
to pid 1 (init).

Hope, that helps someone understanding the code better than I do
to fix this.

Christoph