Made the package compile in termux on android

[arrkiin]

To compile the package in the termux app on android you have to compile the sources with the compiler flag "-fPIC". I added this in an special condition branch. The compiled package is working properly within the following constellation ijavascript -> jp-kernel -> jmp -> zeromq.js

[n-riesco]

@rolftimmermans Would it make sense to move the -fPIC in this PR into the zmq_external case you introduced recently?

[rolftimmermans]

Shouldn't node-gyp add -fPIC already? I don't think it should be necessary to add it explicitly.

[n-riesco]

@arrkiin, would you be able to check whether your PR works without -fPIC?

In fact, you may be able to remove -lzmq as well, if you install zeromq with npm install zeromq --zmq-external.

[arrkiin]

@n-riesco, that what you described was my first attemp to resolve the problem. I cloned the ijavacript repository and did an npm install --zmq-external. The effect was as expected:

Requested to use external libzmq. Skipping download of prebuilt binaries.
Requested to use external libzmq. Skipping libzmq build

But during the linking of the libzmq library it produced the following errror message:

/data/data/com.termux/files/usr/bin/ld: Release/obj.target/zmq/binding.o: relocation R_AARCH64_ADR_PREL_PG_HI21 against symbol `_ZN3zmq7Context3NewERKN3Nan20FunctionCallbackInfoIN2v85ValueEEE' which may bind externally can not be used when making a shared object; recompile with -fPIC

So I digged a lot deeper, cloned the zeromq.js project and did some sole experiments with the zeromq build process. In the end I came up with the changes bundled in this PR. To verify the whole build process I cloned the whole dependency chain ijavascript -> jp-kernel -> jmp -> zeromq.js with modified dependenies. In the end I had a nice ijavascript-kernel on my android device termux-app.

[rolftimmermans]

Well, node-gyp already adds -fPIC in some situations, see https://github.com/nodejs/node-gyp/blob/master/addon.gypi#L140. Maybe a new scenario should be added there?

Deciding which flags need to be added for certain platforms to correctly compile Node.js modules (in general) should be added in the node-gyp project, not in each project separately.

There is nothing specific in ZeroMQ.js which would require -fPIC.

I recommend opening a pull request with node-gyp.

[arrkiin]

Great investigation. Thanks for the hint. I will look into it later this week and do some tests.

[arrkiin]

Looked into https://github.com/nodejs/node-gyp/blob/master/addon.gypi#L140 and did the needed modifications (https://github.com/arrkiin/node-gyp/blob/termux_on_android/addon.gypi#L142).
Now using npm install --zmq-external is giving the proper results. Will create a pull-request for node-gyp, so I close this PR. Thank you for your support.

[arrkiin]

Fyi. Here is my PR for node-gyp (nodejs/node-gyp#1340). So ijavascript and jp-babel were installed without any problems. I like my new possibility to use jupyter on my android device as a scratchpad and idea-lab for python and now also for javascript stuff. @n-riesco, thanks for that. @rolftimmermans thanks for your help, just learned more about npm and node-gyp now.