fix ABI incompatibility problem of some JS direct-connected API

[aydinkim]

As you know, there is a issue when connect rust to c(++) between another ABIs.
So I added some glue code to use JS API normally regardless of ABI difference.

I had also modified the module : rust-mozjs
actual commit is on my local github.
aydinkim/rust-mozjs@35c7752

and the source code diff is attached below.
https://gist.github.com/aydinkim/5450506

[jdm]

I'm willing to commit this for now (after a rebase that clears up the new places that also use JS_GetReservedSlot), but these adhoc changes worry me. We need to sit down and figure out whether we need to wrap all of the relevant JSAPI calls or find some other solution.

[metajack]

Ping? Is this going to get rebased, or is it no longer needed?

[jdm]

We discussed this today, and we believe that a much less intrusive fix is possible. If we define JSVal as a struct containing a u64 in jsapi.rs, that should cause rustc to use the correct calling convention on ARM. Could you try that fix instead?

[ILyoan]

@jdm What a clever and neat idea!!!
I'll try with this idea.

[yichoi]

We have been thinking 2 transitional ideas: one is wrapping with struct like jdm mentioned and the other is a kind of unsafe enum. I agree to struct approach for this issue but I want to know whether there is really general solution on rust side or not.

[ILyoan]

I'm working on this on my rust-mozjs branch and servo branch.
Looks working on x86 linux, but not tested on android yet.
@jdm @yichoi Could you confirm if this is right direction?
If right, I'll rebase it and open PR after huge change from pcwalton landed.

[jdm]

Yes, that looks right to me.

[yichoi]

+1

[ILyoan]

@jdm thinks you for your comments.
I have a patch for this issue but couldn't test it on android device yet.
Close this PR. I'll open another PR after test it on android.