[Debian-med-packaging] Bug#828209: Bug#828209: libssw: FTBFS on non-SSE architectures

[Sascha Steinbiss]

Dear Aaron,

thanks for your report and for caring about the non-x86 archs!

> Builds for libssw failed on the vast majority architectures due to lack
> of support for x86 SSE instructions.  AFAICT, libssw specifically makes a
> point of using these instructions, so support for non-x86 architectures
> is presumably a lost cause.  

Indeed, since regular SW implementations are pretty trivial; this library explicitly uses SSE.

> However, you might still be able to save
> *i386 by explicitly building with -msse or -msse2.  I normally recommend
> *against* using these flags, but the alternative is losing support for
> these architectures altogether.

I would be curious to hear why setting these flags on i386 might salvage the build. I just tried them on a Jessie i386 Vagrant box and the build indeed succeeded for -msse2, but the resulting binaries obviously(?) segfaulted when trying to run them. When you suggested these flags, did you expect me to do anything else than that — I can’t see why code containing SSE instructions would run on i386?

> (All the same, if you do go this route,
> please declare a dependency on sse-support [i386] once that package is
> available, as discussed in #823672.)

Sure, will do that.

> Please update the Architecture: field in debian/control to reflect
> whatever you wind up doing, remembering to account for non-Linux kernels:
> 
>  Architecture: any-amd64 any-i386 any-x32
> 
> or
> 
>  Architecture: any-amd64 any-x32

AFAICS at the moment, I would have to go with the latter. For my purposes (libssw as a dependency for spades) this wouldn’t make much of a difference, as the current SPAdes also only runs on SSE enabled archs (maybe due to the code copy of libssw inside?).

I would be glad if you could briefly comment on why -msse would be able to make i386 work. If you can confirm there’s nothing more I can do (short of implementing a non-SIMD fallback) I would just change the architectures and re-upload.

Thanks
Sascha