Change:
The AVR-Rust post continues to track AVR-LLVM, which is tracking upstream LLVM. That means we are running into changes from the future LLVM 4.0. I figured we could open up this issue now to track the changes required to stay compatible. This is the current list of upgrade hazards. Note that some of the text may be nonsensical as I don't truly grok all the internals of LLVM so some changes are wild stabs in the dark. It's also possible that some failed fix for earlier problems actually caused later problems: [x] DIDescriptorFlags became a real C++ enum and not a bitset () [x] An EH personality is required for every function that can unwind () [x] pass changed header and constructor name () [x] changed API () [x] Bitcode/ReaderWriter.h has been renamed / API changed () () [x] changed API () [x] changed API () [x] prefers over () [x] string type changes () [x] is not guaranteed to be null terminated () [x] changed return types () [x] Archive support changed error handling types () [x] Teach Rust about an LLVM 4.0 API change for creating debug info for global variables () [x] Check all errors in LLVMRustArchiveIterator API () [x] Upgrade emscripten (kripken/emscripten-fastcomp, kripken/emscripten-fastcomp-clang) [x] Alignment now represented with 32 bits instead of 64 () [x] API changed again () [x] now takes an instead of a and () [x] Symbol lookup error when linking dylibs () [x] Undefined behavior in tests () [x] Unoptimised builds of compilerbuiltins on ARM have references to () A WIP PR that performs the upgrade! Some issues whose resolution is believed to be blocked on LLVM 4.0: [ ]
Next time we do this upgrade we'll need emscripten to do it to. It would be good if we could pull in a working llvm wasm backend in the same upgrade, but that may not be ready before the end of the year.
For the record, I am also working with a fork of LLVM that is tracking upstream (not AVR-LLVM but similar in spirit) and am starting to work on this now. I'm looking through the AVR-Rust commits and I'd love to coordinate --- feel free to ping me on IRC () or via mail!
Note that there is a regression reported against llvm 4.0 regarding the powi intrinsic on armhf targets: I'm explicitly mentioning this here, because there were previously problems with it, see and related issues. Also cc rust-lang-nursery/compiler-builtins, an issue about the same problem in the compiler-rt rust port.
To clarify what I think the is referring to (correct me if I'm wrong) In LLVM 3.9 and before, the calling convention LLVM used with the powidf2 and powisf2 intrinsics was basically the C calling convention In LLVM 4.0, the backend was corrected to expect these intrinsics to have the aapcs calling convention One person that aapcs is expected for powis2f and powid2f, while another a claiming that the normal C calling convention should be used. So it seems that if the LLVM change is not reverted (expected powisf2 to be aapcs) then we need to update our definition. This is going to be a huge PITA for supporting multiple LLVM versions as well. We need to select the calling convention depending on the LLVM version as well...
Any objections to doing that coordination here on GitHub, or on one of our forks?
I don't have strong preferences for the communication channel.
should address what is listed as API changes" above (the core of the change is in how attributes are represented).
I would prefer to upstream LLVM 4.0 compatibility patches sooner rather than later. That includes my own work obviously, but I'm also looking at the commits I cherry-picked from AVR-Rust. In particular, looks like a reasonable simplification even independent of LLVM 4.0 compatibility, and looks like a nice little self-contained fix. Could you create PRs for those? (If you don't have the time but are otherwise fine with upstreaming, I'd be happy to manage that, giving proper credit of course.)
Absolutely! I wasn't really sure how much we could expect LLVM 4 to change as it goes towards stable / how much churn the Rust maintainers would want to put up with. I'll get those pulled out and submitted soon. I think I'm also starting to understand some of the silly error handling that the new LLVM does.
Awesome, thanks in advance!
BTW the PR reference for "llvm::AttrBuilder changed API" is wrong, it points at this issue instead of
Does anyone have ETA? I'd like to know when I can use AVR. :)
You should follow along at avr-rust/rust for the AVR-specific issues. Upgrading to LLVM 4 will not magically yield AVR support.
Ok, thank you!
I've created for the API change.
I've also created for another debug info API change.
After putting all of those patches on top of master, was successfully built. I got several undefined references, most likely due to my local LLVM setup.
I think the next step after all those patches land is to allow LLVM 4.0 in the configure/rustbuild scripts and then actually update the submodule.
We'll also need to fix that AAPCS bug first, I just noticed it
Don't forget : I think that means that the Rust fork of LLVM is following the Emscripten fork of LLVM, thus Emscripten needs to upgrade to LLVM 4.0 / master before Rust can.
And I'm hoping to supersede it with
I just ran into which changed the alignment from u64 to u32. Will think about a proper fix later, unless someone beats me to it (but should merge first to avoid further conflicts).
And it says So, that will be "exciting".
Is there much left blocking an upgrade?
This: Has to be done too but I don't know if it's currently being worked on. Any info on that ^?
No nobody is actively working on an emscripten upgrade. Since even when that is done it will probably take a lot of work to land an LLVM upgrade, there's probably more we can do to prepare. Once we decide we want to do it, somebody can prepare a patch to throw at the bots. It seems likely stuff will not work and it will be a slog to fix it all, which will give us time. We don't need emcc to generate wasm stds, just a fairly small patch on our LLVM branch that will hopefully port without much difficulty. So if somebody feels motivated, it's not too soon to start going after it. As to the emscripten upgrade, we should at least let know that we're starting to think seriously about doing the upgrade, and need emscripten to upgrade LLVM too. It seems like that could be a big effort. Another alternative is to use the LLVM wasm backend, but I still have not heard that it is generally usable yet. cc
I can look into the effort needed to update emscripten's fastcomp LLVM version, but I need to know a commit to aim for. Sounds like the goal here is 4.0, which hasn't released yet, so I guess I have to wait on that?
So far as AVR is concerned, any commit within the last month will do. There will likely be a few more months until 4.0 is actually tagged (every ~6 months a new release is made). It is quite common for projects to track LLVM master, which I'm personally a fan of.
But is it common to release snapshots from LLVM master? When LLVM itself only releases every 6 months, it seems incongruous for Rust to pick arbitrary snapshots in its 6-week release cycle.
LLVM 4.0 will branch in a week and the final release will happen in late feburary (schedule says 21st for final tag, but this is flexible IIRC).
From the llvm-dev mailing list:
branch has happened
An update on the "powidf2 / powisf2 calling convention changed" situation: The regression has been fixed on llvm master () however from what I can tell the fixes are not yet in the 4.0 branch, although the fix may be backported ().
I've started working on updating emscripten kripken/emscripten-fastcomp kripken/emscripten-fastcomp-clang I've also created a new bug requesting that the regression fix be merged into 4.0 .
says the emcc LLVM upgrade is ready to go. or are we prepared to begin the Rust LLVM upgrade? I think what needs to happen is to submit the Rust PR and start throwing it against the bots. Once it looks like that is close to landing then we'll have to coordinate both project's upgrades to minimize the breakage window where rustc and emcc have different backends. I'm not sure how best to do that - we might just try to upgrade as simultaneously as possible and accept up to a few days of breakage, or we might ask emscripten to stage their build such that they can swap their incoming branch right after we land to master. needs to know the exact LLVM commit we're moving to as well, and that will become clear once the PR starts working through the queue. The stars are aligning. Let's make this happen. Thanks for doing the fastcomp upgrade.
We are not fully compatible with LLVM 4.0. I have heard from at least one person (on IRC) that building against stock LLVM 4.0 (RC) does not work. I haven't personally inspected all failures, but there's at least two things still missing: (and possibly ). It shouldn't be a conceptually difficult patch to apply the equivalent changes to rustc, but possibly a big diff. I haven't digested the implications yet, but it might be a relatively simple change localized to the function in that currently calls .
The fix has been merged into the 4.0 release (). I'm going to try and build Rust against stock LLVM 4.0 and figure out what needs modifying.
On top of what mentioned: now takes an instead of a and ()
I've got a half-baked patch to use the new signature for I'm not familiar enough with Rust internals to finish it off. I ran into a problem in as it is given a but in order to use we need a . We need to call in order to build an instance of .
I've opened for the change that mentioned. I've also opened for the 32-bit alignment change. I believe that is the only thing we need to update aside from these two PRs in order to get the compiler to successfully be built with LLVM 4.0.
So to summarize where we are with LLVM 4 (correct me if I'm wrong): 4.0 will be released in about 1 week (2/21). are no known issues with supporting LLVM 4.0, but there are probably issues that will be discovered once we try to use it in nightlies. runs on in-tree LLVM + LLVM 3.7 (so PRs haven't actually been tested on LLVM 4.0 yet). support LLVM back to ~3.6(?)~ 3.7 and will continue to support it until either: a. It's so old that it can be removed without bothering package maintainers b. We need at least version X in order to fix an important bug c. The API is so different from version Y that it's a huge pain to support will open a PR to update the submodule shortly after release but it will take a month to land due to: a. Waiting for emscripten ( -) b. Bugs in upstream c. Missed LLVM API changes d. Making bors happy e. All of the above
Thanks for the summary The only correction I'd make is that in your point (4) you can s/3.6/3.7/, but otherwise it's accurate :) If you'd like to start preparing a PR to update to LLVM 4.0 I don't think we need to block waiting for LLVM itself to release 4.0. Currently only one Travis builder runs on each PR but we could temporarily allow more builders running on an LLVM 4.0 PR to start weeding out bugs before it hits
I gave it a go but I don't think my git-fu (or patience) is strong enough to handle a big merge like this. What I can do is try to run rustc with upstream LLVM and file/fix issues as I find them. There is at least one issue remaining as of (details to come).
Whoever ends up doing the LLVM upgrade, please also upgrade the compiler-rt submodule so that the sanitizer related LLVM passes don't diverge from what the sanitizer runtimes expect.
In fact, if you upgrade before the release, they usually mention your project in the release notes. :)
So whats the next issue(s) to subscribe to in the race-to-AVR? :)
As says on , we can integrate the latest Rust master into the avr-rust compiler. After that, we can spend some time getting compiling for AVR. Once that is working, we could then start looking into upstreaming the AVR target to Rust.
AVR-specific issues can be raised / tracked in For example, there are two that I'm aware of right now:
has been closed, so that can be checked off in the top post.

Discussion:
# 32/64-bit MinGW builds. # <del> # The MinGW builds unfortunately have to both download a custom toolchain and # avoid the one installed by AppVeyor by default. Interestingly, though, for # different reasons! </del> <ins> # We are using MinGW with posix threads since LLVM does not compile with # the win32 threads version due to missing support for C++'s std::thread. </ins> # <del> # For 32-bit the installed gcc toolchain on AppVeyor uses the pthread # threading model. This is unfortunately not what we want, and if we compile # with it then there's lots of link errors in the standard library (undefined # references to pthread symbols). # # For 64-bit the installed gcc toolchain is currently 5.3.0 which # unfortunately segfaults on Windows with --enable-llvm-assertions (segfaults # in LLVM). See rust-lang/rust#28445 for more information, but to work around # this we go back in time to 4.9.2 specifically. </del> <ins> # Instead of relying on the MinGW version installed on appveryor we download # and install one ourselves so we won't be surprised by changes to appveyor's # build image. </ins> # # Finally, note that the downloads below are all in the `rust-lang-ci` S3 # bucket, but they cleraly didn't originate there! The downloads originally # came from the mingw-w64 SourceForge download site. Unfortunately # SourceForge is notoriously flaky, so we mirror it on our own infrastructure. <del> # # And as a final point of note, the 32-bit MinGW build using the makefiles do # *not* use debug assertions and llvm assertions. This is because they take # too long on appveyor and this is tested by rustbuild below. </del> - MSYS_BITS: 32 RUST_CONFIGURE_ARGS: --build=i686-pc-windows-gnu --enable-ninja SCRIPT: python x.py test MINGW_URL: https://s3.amazonaws.com/rust-lang-ci/rust-ci-mirror <del> MINGW_ARCHIVE: i686-6.2.0-release-win32-dwarf-rt_v5-rev1.7z </del> <ins> MINGW_ARCHIVE: i686-6.2.0-release-posix-dwarf-rt_v5-rev1.7z </ins> MINGW_DIR: mingw32 - MSYS_BITS: 64 SCRIPT: python x.py test RUST_CONFIGURE_ARGS: --build=x86_64-pc-windows-gnu --enable-ninja MINGW_URL: https://s3.amazonaws.com/rust-lang-ci/rust-ci-mirror <del> MINGW_ARCHIVE: x86_64-6.2.0-release-win32-seh-rt_v5-rev1.7z </del> <ins> MINGW_ARCHIVE: x86_64-6.2.0-release-posix-seh-rt_v5-rev1.7z </ins> MINGW_DIR: mingw64 # 32/64 bit MSVC and GNU deployment

RUST_CONFIGURE_ARGS: --build=i686-pc-windows-gnu --enable-extended --enable-ninja SCRIPT: python x.py dist MINGW_URL: https://s3.amazonaws.com/rust-lang-ci/rust-ci-mirror <del> MINGW_ARCHIVE: i686-6.2.0-release-win32-dwarf-rt_v5-rev1.7z </del> <ins> MINGW_ARCHIVE: i686-6.2.0-release-posix-dwarf-rt_v5-rev1.7z </ins> MINGW_DIR: mingw32 DEPLOY: 1 - MSYS_BITS: 64 SCRIPT: python x.py dist RUST_CONFIGURE_ARGS: --build=x86_64-pc-windows-gnu --enable-extended --enable-ninja MINGW_URL: https://s3.amazonaws.com/rust-lang-ci/rust-ci-mirror <del> MINGW_ARCHIVE: x86_64-6.2.0-release-win32-seh-rt_v5-rev1.7z </del> <ins> MINGW_ARCHIVE: x86_64-6.2.0-release-posix-seh-rt_v5-rev1.7z </ins> MINGW_DIR: mingw64 DEPLOY: 1

COPY build-emscripten.sh /tmp/ RUN ./build-emscripten.sh ENV PATH=$PATH:/tmp/emsdk_portable <del> ENV PATH=$PATH:/tmp/emsdk_portable/clang/tag-e1.37.1/build_tag-e1.37.1_32/bin </del> <ins> ENV PATH=$PATH:/tmp/emsdk_portable/clang/tag-e1.37.10/build_tag-e1.37.10_32/bin </ins> ENV PATH=$PATH:/tmp/emsdk_portable/node/4.1.1_32bit/bin <del> ENV PATH=$PATH:/tmp/emsdk_portable/emscripten/tag-1.37.1 ENV EMSCRIPTEN=/tmp/emsdk_portable/emscripten/tag-1.37.1 </del> <ins> ENV PATH=$PATH:/tmp/emsdk_portable/emscripten/tag-1.37.10 ENV EMSCRIPTEN=/tmp/emsdk_portable/emscripten/tag-1.37.10 </ins> ENV RUST_CONFIGURE_ARGS --target=asmjs-unknown-emscripten

source emsdk_portable/emsdk_env.sh hide_output emsdk update <del> hide_output emsdk install --build=Release sdk-tag-1.37.1-32bit hide_output emsdk activate --build=Release sdk-tag-1.37.1-32bit </del> <ins> hide_output emsdk install --build=Release sdk-tag-1.37.10-32bit hide_output emsdk activate --build=Release sdk-tag-1.37.10-32bit </ins>

<del> Subproject commit d30da544a8afc5d78391dee270bdf40e74a215d3 </del> <ins> Subproject commit c8a8767c56ad3d3f4eb45c87b95026936fb9aa35 </ins>

} if target.contains("arm") && !target.contains("ios") { <ins> // (At least) udivsi3.S is broken for Thumb 1 which our gcc uses by // default, we don't want Thumb 2 since it isn't supported on some // devices, so disable thumb entirely. // Upstream bug: https://bugs.llvm.org/show_bug.cgi?id=32492 cfg.define("__ARM_ARCH_ISA_THUMB", Some("0")); </ins> sources.extend(&["arm/aeabi_cdcmp.S", "arm/aeabi_cdcmpeq_check_nan.c", "arm/aeabi_cfcmp.S",

<del> Subproject commit 2e951c3ae354bcbd2e50b30798e232949a926b75 </del> <ins> Subproject commit a884d21cc5f0b23a1693d1e872fd8998a4fdd17f </ins>

// write_volatile causes an LLVM assert with composite types <ins> // ignore-emscripten See #41299: probably a bad optimization </ins> #![feature(volatile)] use std::ptr::{read_volatile, write_volatile};

exit_success_if_unwind::bar(do_panic); } } <del> let s = Command::new(env::args_os().next().unwrap()).arg("foo").status(); </del> <ins> let mut cmd = Command::new(env::args_os().next().unwrap()); cmd.arg("foo"); // ARMv6 hanges while printing the backtrace, see #41004 if cfg!(target_arch = "arm") && cfg!(target_env = "gnu") { cmd.env("RUST_BACKTRACE", "0"); } let s = cmd.status(); </ins> assert!(s.unwrap().code() != Some(0)); }

panic!("try to catch me"); } } <del> let s = Command::new(env::args_os().next().unwrap()).arg("foo").status(); </del> <ins> let mut cmd = Command::new(env::args_os().next().unwrap()); cmd.arg("foo"); // ARMv6 hanges while printing the backtrace, see #41004 if cfg!(target_arch = "arm") && cfg!(target_env = "gnu") { cmd.env("RUST_BACKTRACE", "0"); } let s = cmd.status(); </ins> assert!(s.unwrap().code() != Some(0)); }