Re: [Xen-devel] [PATCH 2/3] build: allow picking the env values for compiler variables

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Jan Beulich writes ("Re: [PATCH 2/3] build: allow picking the env values for 
compiler variables"):
> On 20.08.2019 09:58, Roger Pau Monné  wrote:
> > I don't have things 'left' in the environment, neither have most build
> > systems AFAIK. I do have things set that I want the build to
> > acknowledge, instead of fight against it.
> 
> My view is this: XEN_* things coming from the environment are fine.
> Generic (i.e. project agnostic) variables (like CC) otoh would
> better be ignored, as it's not clear for what purpose they've been
> set. (Istr a case where some FORTIFY option was set by RPM build
> environments, breaking our build.) They may well have been meant
> for some other project.

CC is set *specifically to cause build systems's like Xen's to use
that compiler*.  That is its purpose.  It should be honoured, not
ignored.

Likewise FORTIFY, even though it broke something.  FORTIFY_SOURCE was
set specifically to cause the changes it did.  The people who set it
didn't see all the implications, but that change *was* their design
intent and the bugs were real bugs in what they were trying to do.

> Question is whether to take the above just for the hypervisor part
> of the build, or also the tool stack etc ones.

*Definitely* for the toolstack build, we should honour CC et al.

The hypervisor is a more subtle question because people who set these
variables often forget to think about kernel code, embedded code,
etc.  That's what happened with FORTIFY_SOURCE.  However, I would
argue that it is better, in such a situation, to honour the variable
and break the build, than it is to simply ignore it.

Ian.

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