[Sparc] Account for bias in stack readjustment

[glaubitz]

While working on bootstrapping rustc for sparc64, Michael Karcher discovered that LLVM may generate code where the stack alignment on sparc64 is incorrect which results in rustc segfaulting on sparc64 [1].

Michael created a crude hack which fixed the issue and therefore proved his theory. James Clarke later came up with a proper patch which he has submitted upstream [2].

I have tested both Michael's and James' patch and both fix the segfault of rustc on sparc64. Since Michael's patch does deal with alignment larger than 4k and may also not fix corrupted stack pointers, we chose to use
James' patch.

The patch has already been merged into the llvm-toolchain-4.0 package [3].

Thanks,
Adrian

[1] http://lists.llvm.org/pipermail/llvm-dev/2017-October/118620.html
[2] https://reviews.llvm.org/D39425
[3] https://anonscm.debian.org/viewvc/pkg-llvm?view=revision&revision=2849

[glaubitz]

CC @jrtc27 @karcherm

[alexcrichton]

Thanks for the PR! Is this in upstream LLVM yet?

[glaubitz]

It has been submitted upstream, but not merged yet.

See: https://reviews.llvm.org/D39425

[alexcrichton]

Ok! Let's hold off on merging until this is upstream?

[glaubitz]

That's up to you.

We just won't be able to build a working compiler on sparc64/sparcv9 before this fix has been merged.

[alexcrichton]

Ok yeah it's just standard procedure for us to wait until patches like this are upstream before merging.

[glaubitz]

@alexcrichton It has been merged upstream now, see:

https://reviews.llvm.org/D39425

I have updated the branch to include the changes @jrtc27 made to the testsuite. So the change matches what upstream merged now.

Can you pull the change?

[jrtc27]

Actually it still hasn't been merged, just approved; I've pinged the review again.

[glaubitz]

Since this patch affects sparc64 only and since it unbreaks the Rust compiler on Linux/sparc64, can we maybe get an exception for getting it merged?

It's the only things that keeps us from having a working Rust compiler on Linux/sparc64 at the moment.

[glaubitz]

@alexcrichton It has been merged now upstream. Could we get this merged here now as well?

See: https://reviews.llvm.org/rL323643

[alexcrichton]

Sure thing, thanks for getting this upstreamed!

[glaubitz]

Thanks a lot! I just saw that there is a 6.0 LLVM branch now. Should I open a PR for this branch as well so the patch lands there, too?

[alexcrichton]

Ah no need! I went ahead an put the commit on the branch

[glaubitz]

Wow, you were so fast that it was already there when I just pulled to check whether's it's necessary :D.