Re: [Xen-devel] [PATCH] xen/common: Drop function calls for Xen compile/version information

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Jan 18, 2017 at 11:10:40AM -0500, Konrad Rzeszutek Wilk wrote:
> On Wed, Jan 18, 2017 at 10:13:34AM +0000, Roger Pau Monné wrote:
> > On Tue, Jan 17, 2017 at 03:46:30PM -0500, Konrad Rzeszutek Wilk wrote:
> > > > > Is this patch of yours that neccessary? Could at least some of the
> > > > > functions still exist?
> > > > 
> > > > Well.  This patch is manually doing what LTO would do automatically when
> > > > it has a cross-translation-unit view of things, and come to the
> > > > conclusion that in all cases, inlining cross-unit will make the calling
> > > > code shorter, and allow the functions to be elided entirely.
> > > > 
> > > > I take it from this that noone has tried livepatching an LTO build of 
> > > > Xen.
> > > 
> > > Roger did build it (FreeBSD uses it), but I don't think he tried
> > > the test-cases.
> > 
> > I've tried livepatch, but not LTO, neither on it's own.
> 
> Gotcha.
> > 
> > > Wait, I think he may have as his patch: 
> > > f8c66c2ad2efdb281e4ebf15bf329d73c4f02ce7
> > > Author: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> > > Date:   Tue May 3 12:55:09 2016 +0200
> > > 
> > >     xen/xsplice: add ELFOSABI_FREEBSD as a supported OSABI for payloads
> > > 
> > > implies that he did build an payload (and I remember us trying to figure
> > > out if the issues he had been hitting were due to LTO or something else).
> > 
> > IIRC issues where related to not translating error codes from the return of 
> > the
> > livepatch hypercalls, and the patch upload tool refusing to upload patches 
> > with
> > ELFOSABI_FREEBSD instead of ELFOSABI_NONE (which I assume is what Linux 
> > uses).
> > 
> > It's been sometime since I've tried livepatch with FreeBSD, so I could give 
> > it
> > a spin if you think there's a chance things might have broken.
> 
> That is OK. 
> 
> I think I can also try myself to build Xen with LTO on Linux and see how
> the test-cases fare.
> 
> Not sure what is involved but I will find out.
> 
> And to answer Andrew's question - No, nobody tried LTO with livepatching then 
> :-(

TBH, I think nobody has tried LTO on it's own in a long time, much less with
livepatch. Adding Wei who recently sent some LTO makefile fixes, maybe he tried
it.

Roger.

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