I ran into something similar once. Don't use the -neon switch for AARCH64 because it's built in.
On 2/27/19, Steve McIntyre <[email protected]> wrote: > On Wed, Feb 27, 2019 at 06:30:36PM -0500, Jeffrey Walton wrote: >>On Wed, Feb 27, 2019 at 5:46 PM Steve McIntyre <[email protected]> wrote: >>> >>> So, I've got to ask - what hardware are you likely targeting here >>> where it matters to build stuff for armel yet also use NEON if it's >>> available? Most people with hardware that *can* do NEON should be >>> using armhf, surely? >> >>Yeah, I know what you are saying. >> >>The problem in practice with mainstream compilers is (1) ARM and the >>ACLE defines are a mess, (2) -march=native does not work like on i686 >>or x86_64, and (3) RTFM does not work. >> >>For a regular user who wants to use Debian on ARM we need to figure >>out how to build to the least capable machine (like ARMv5 or ARMv6) >>while making more capable features (like NEON) available. > > So this is a place where the world is just *different* compared to x86 > - the different versions of the ARM architectures have signficantly > different capabilities. If you're looking to build something that > performs well on a modern v7 CPU, compilling for v5 is a > mistake. You'll be using the wrong locking primitives, barriers, > etc. Equally, the features you're going to be looking for (like SMP, > NEON) just don't make sense / don't exist on v5 CPUs. > >>User's don't want to RTFM to figure out what compiler switches to use. >>They just want things to work. The compilers don't make it any easier >>because -march=native does not work on ARM. > > It's a much wider world out there. :-/ > >>So the use case we target is, user want the most from their hardware >>without reading the manual to configure properly. That means we have >>to go through extra gyrations when building. >> >>(I know we bring it on ourselves. We could easily say fuck it - the >>user did not bother to read a man page so its the user's problem. But >>I'm in the camp that common cases should just work for folks. Folks >>should not need to read a manual to make the common case work). > > Agreed. But it might not actually be *possible* to do some of the > optimisation stuff you're looking at, depending on the CPUs > involved. This is basically one of the reasons we started the armhf > port - it's a higher baseline that makes more sense for modern ARMv7 > CPUs, while still making it possible for people to use the older ARMv5 > cores out there. > > -- > Steve McIntyre, Cambridge, UK. > [email protected] > "Yes, of course duct tape works in a near-vacuum. Duct tape works > anywhere. Duct tape is magic and should be worshipped." > -― Andy Weir, "The Martian" > > -- ------------- No, I won't call it "climate change", do you have a "reality problem"? - AB1JX Cities are cages built to contain excess people and keep them from cluttering up nature. Impeach Impeach Impeach Impeach Impeach Impeach Impeach Impeach
