Re: [KEXEC][2.5.69] Re: Updated kexec diffs...

[ebiederm@xmission.com (Eric W. Biederman)]

Andrew Morton <akpm@digeo.com> writes:

> ebiederm@xmission.com (Eric W. Biederman) wrote:
> >
> > And Andrew has it in 2.5.69-mm4 and is busy pestering me about compile
> >  errors. 
> 
> I'm like that.

And I appreciate it.  This was mostly an observation there was
something reminding me to get back and fix the issue.
 
> I've dropped out a lot of the NORET stuff.  It generates warnings on all
> other architectures, because their machine_restart, machine_halt and
> machine_power_off definitions don't have necessary attributes and don't
> have the while(1); at the end.

Yes there is a big const correctness type problem here.

First for machine_restart it is 100% correct.  And at least sys_reboot
assumes that machine_restart will not return, even before my patch.

And I don't know of a case where it makes sense for machine_halt and
machine_power_off to return.  Hence I deliberately made those cases
the same.  Especially as every real implementation I traced does not
return.  It is only the stupid cases like on x86 where we don't do
anything that these routines actually return.

In the context of my patch stop_this_cpu needs to be marked noreturn.
As long as the fundamental routines get marked I don't expect to see
a lot of routines getting a while(1);  I admit stop_apics also
needs a while(1); but only because gcc cannot trace it.

And since this also generates warnings on other architectures
it looks like someone (me) needs to go through the various
architectures and add a bunch of noreturn attributes to
the appropriate functions.

The basic question is for documenting and enforcing the noreturn
dependency.  Is it more of a help or a hindrance to use gcc noreturn
tag?

And while I am pretty certain this is the correct thing to do I
should break this out from the reboot_on_bsp patch.  With the
other architectures involved this is enough of a separate issue that a
second set of patches is needed to maintain this cleanly.

Eric