Re: [Xen-devel] [PATCH v2 0/6] Remove dependency on __LINE__

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 03/09/2017 10:34 AM, Jan Beulich wrote:
> > > > On 08.03.17 at 18:46, <ross.lagerwall@xxxxxxxxxx> wrote:
> > Sorry for the long delay since the first version of this series
> > (previously called "Make building xSplice patches easier").  Here is a
> > set of changes that remove the use of __LINE__ when building with NDEBUG
> > and LivePatch enabled.  Tested to boot on x86.  Compile-tested on arm.
> What I'm missing here is an evaluation of possible alternatives, as
> converting from __LINE__ to code addresses implies an extra step
> when wanting to look up the place where a problem occurred,
> which I generally consider undesirable. For example, I had briefly
> discussed with Andrew the addition of #line directives, but iirc he
> had indicated some issue with that. Furthermore there is the
> option (at least for some of the more simple patches) of squeezing
> more than one statement on a single line, perhaps just for patch
> creation. And I guess one can think of more.
Both of the options you suggested require extra work when building a 
live patch. This series is intended to remove that extra work as the 
process is already more difficult than I'd like.
I don't think using addr2line is much harder than looking up the line 
number directly, especially as it is something that needs to be done for 
many other crashes. On your suggestion, use of __LINE__ is disabled only 
when CONFIG_LIVEPATCH=y and NDEBUG which means that in a typical 
development scenario, you'd still get line numbers. They would be 
removed only for "release" builds in which it is likely that the source 
code & debuginfo is archived somewhere such that looking up a line 
number requires several steps anyway. I could suggest making it a 
separate config option but IIRC you prefer to limit the number of config 
options.
--
Ross Lagerwall

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