Hi,
I spent some time trying to cross-compile NumPy for Linux ARM64 on a
macOS host as part of an OpenWRT compilation [1]. It was not so bad but
certainly not trivial and I was wondering if we could use my experience
to help streamline the process.
I encountered two challenges:
1. Python distutils did not allow me to provide a proper cross-ranlib
program path. I opened an issue for this on the Python bug tracker [2].
2. numpy distutils scripts check sys.platform in many places.
sys.platform returns the platform on which compilation occurs (darwin in
my case) which in case of cross-compilation is not the one on which the
code will be run (linux). This of course results in invalid compiler and
linker flags.
I made a quick'n'dirty fix [3] and got numpy to compile and run
correctly (but I have yet to run the full test suite). Of course this is
not a proper way to solve this so I was hoping to get some feedback on
the preferred/best way. I did not find any info about an official way to
do this with distutils.
One idea (from @commodo on GitHub) would be to just change my hardcoded
string ("Linux") to something like this:
target_platform = os.getenviron(“TARGET_PLATFORM”, sys.platform)
It could also be further refactored by moving it to a single place but
while certainly more elegant and "proper" it may ultimately make it less
readable and harder to follow. I am also unsure where would be the best
place to put it and how to pass it around to other modules.
[1]: https://github.com/openwrt/packages/pull/9797
[2]: https://bugs.python.org/issue37916
[3]:
https://github.com/openwrt/packages/pull/9797/commits/e701e122fb9c78d5cecffb88c1d750178a239083#diff-1ea8d839590bcdc406854d3998a96704
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