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

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Julien Grall <julien.grall@arm.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Jan Beulich <JBeulich@suse.com>,
	Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH] xen/common: Drop function calls for Xen compile/version information
Date: Wed, 18 Jan 2017 11:10:40 -0500	[thread overview]
Message-ID: <20170118161040.GC4940@char.us.oracle.com> (raw)
In-Reply-To: <20170118101334.2acxof7acl3gcy2n@dhcp-3-221.uk.xensource.com>

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@citrix.com>
> > 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 :-(

> 
> Roger.

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