Re: [PATCH v2 02/10] Add Aarch64 SVE Linux headers

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 2018-06-12 11:11, Pedro Alves wrote:
> On 06/12/2018 04:06 PM, Simon Marchi wrote:
> > I think that would be a good compromise.  By default, building on a 
> > machine with an older kernel would exclude SVE support.  But it would 
> > be possible to add it by pointing to the headers of a recent kernel.  
> > So when building on a machine with an older kernel...
> >
> > - ... without any special flags, you don't get SVE support.
> > - ... with just --enable-sve, you get a configure error.
> > - ... with --enable-sve and CFLAGS/CXXFLAGS pointing to headers of a 
> > kernel w/ SVE macros, you get SVE support.
> >
> > Does that make sense?
> Yes.  Not sure an --enable-sve switch is necessary (compared to just 
> having
> headers vs not having headers), but I'd be fine with having one.

I think it is useful if you want to make sure your build will have the 
support:

- auto/not specified: include the support if the prerequisites are 
available
- enable: include the support, error at configure if prerequisites are 
missing
- disable: don't include the support

Otherwise, just a typo in your include path can result in a build 
without the feature you want, and you only discover it later, that's 
annoying.

Simon