sage with 64 bit openblas

[timokau]

By default, openblas compiles with a 32 bit interface (even when the binary is 64 bit). To build with the 64 bit interface, you have to set the INTERFACE64 environment variable. Here is some discussion about the differences.

When just naively enabling 64 bit openblas in sage, we get various segfaults. First during docbuild and then more during testing (see attached logs).
On nix I even get those failures if only flint is compiled with openblas64, even though flint doesn't even really need openblas.

Component: packages: standard

Keywords: openblas

Branch/Commit: public/26000 @ e3ddaf8

Issue created by migration from https://trac.sagemath.org/ticket/26000

[timokau]

Attachment: tests.log

[timokau]

comment:1

Attachment: dochtml.log

[timokau]

Commit: e3ddaf8

[timokau]

Branch: public/26000

[timokau]

New commits:

e3ddaf8

Enable 64 bit interface for openblas

[jdemeyer]

Replying to @timokau:

By default, openblas compiles with a 32 bit interface (even when the binary is 64 bit). To build with the 64 bit interface, you have to set the INTERFACE64 environment variable. Here is some discussion about the differences.

After reading that page, I don't think that we should enable INTERFACE64. An environment variable to change the API? That makes no sense to me...

So why should we do this?

[timokau]

comment:4

Did you maybe misunderstand that? Its a configure-time variable, nothing unusual. Not runtime.

The advantages would be higher precision data types and higher compatibility with system openblas.

[jdemeyer]

comment:5

Replying to @timokau:

higher compatibility with system openblas.

Do distros set INTERFACE64?

[timokau]

comment:6

In nix we have two versions, openblas and openblasCompat. openblas uses INTERFACE64 on 64 bit machines while openblasCompat always uses 32.

Its harder for other distros to have multiple variants of the same library though, so maybe they just use the Compat version all the time. I don't know for sure. Either way, if we figure out where the INTERFACE64 failures are coming from we would keep compatibility for 32 bit anyways. So it would be a win-win.

[jdemeyer]

comment:7

Replying to @timokau:

In nix we have two versions, openblas and openblasCompat. openblas uses INTERFACE64 on 64 bit machines while openblasCompat always uses 32.

So then use openblasCompat.

It's still not clear which bug this ticket is supposed to fix...

[timokau]

comment:8

Replying to @jdemeyer:

It's still not clear which bug this ticket is supposed to fix...

Its an enhancement. Nix specific, using openblasCompat means we also have to build two versions of flint and two versions of all the sage dependencies that depend on flint. Thats a bit annoying.

In general, 64 bit is not only the future, I would argue it is the present. I don't know how long other distros will keep INTERFACET64=0 (if they currently do that). And ignoring distros for the moment, the main reason for 64 bit are 64 bit datatypes of course.