Submit llvm patches required to build zinc

[farcaller]

A tracking bug. Zinc couldn't be compiled without modifying rustc first.

Patches

ML Thread

[bharrisau]

Would be worth also submitting a pull request to rust-lang/llvm

[farcaller]

I'll give it a go if there would be no updates in llvm ML in a reasonable time.

[bharrisau]

This was working fine previously from this pull req rust-lang/llvm#4, looks like it was undone when a similar patch was submitted to LLVM.

[farcaller]

I've discussed the issue with acrichto@ over IRC a few days ago and it seems that the actual patch to llvm was modified as part of submission, so that the bug resurfaced. It seems that noone really cares that much, as it breaks a limited number of projects of those who try to run rust code on cortex-m :)

I got a test case to back my change, but I want to get some comments on the 256-bytes padding after the stack, I can't just go and suggest to remove it until I have a better understanding on why it was there in the first place.

[bharrisau]

@farcaller - is this still relevant?

[farcaller]

Yes. There's an RFC on getting rid of morestack, waiting on some resolution in there.

[bgamari]

@farcaller how about now? Also, could you give a reference to the RFC in question?

[farcaller]

This is closed in favour of freestanding support in rust.