Re: sse{2,3,4.2}, altivec, neon, ...

[Ian Campbell <ijc@hellion.org.uk>]

On Sun, 2017-08-06 at 17:27 +0200, Adam Borowski wrote:
> On Sun, Aug 06, 2017 at 09:16:48AM +0100, Ian Campbell wrote:
> > What is the expected interaction with the hwcaps based library
> > installed paths? (/usr/lib/i386-linux-gnu/i686/{sse2,cmov}).
> > Presumably
> > libraries would still be expected to use those as appropriate?
> 
> hwcaps implies runtime detection, ie, your code runs on all CPUs, both those
> with or without the extension in question. No need to say "sorry I can't
> support the baseline" if you can.

I was asking about e.g. a library which only supports, say, sse2 would
not run without that extension, so no baseline support is present.

In that case should the library package both depend on your new
metapackage _and_ also install to the sse2 hwcap directory, or are you
were suggesting that if you depend on the metapackage then installing
the main base library dir is ok.

The practical difference would be between a library-not-found from the
dynamic linker vs an undef-instruction at runtime (assuming no further
runtime check is present) in the case where a user has chosen to
override the metapackage somehow and is running on an unsupported
platform.

Ian.