Compile rustc+LLVM to wasm #6

oligamiq · 2024-09-08T18:46:06Z

LLVM backend is now available.
It works by changing config.llvm.toml to config.toml.
This allows rustc to compile against wasm32-wasip1-threads.
https://github.com/YoWASP/clang was used as a reference.

Since wasm-ld can also be used on wasi by that project, All that remains is for browser_wasi_shim to support threading, and it should be possible to compile on the browser.

cargo is going to create a project that wraps this project like the project above, which together with rustc will generate one wasm as a driver like YoWASP/clang project.

Problem is that llvm is not patched by rust and the version of llvm is higher than rust. compiler/rustc_target/src/target_features.rs has been changed because of that.
Also, the cc library has been raised to a version that supports building to wasi.
In addition, I upgraded the wasi-sdk version.

wasm and sysroot are available at https://github.com/oligamiq/rust_wasm/
so please use them if you want to try them.

Please forgive the messy commit.

bjorn3 · 2024-09-08T19:46:27Z

Thanks a lot for this PR! I'm currently at a conference, so I probably won't get to reviewing for a couple of days. If I don't review it within a week or so feel free to ping me.

bjorn3

Sorry for the late reply. I've rebased the wasm changes and created the new compile_rustc_for_wasm16 branch for this. Would you mind rebasing and changing the target of this PR to that branch? You can use the same edit button that allows changing the PR title and then clicking on the button next to "oligamiq wants to merge 86 commits into". Also squashing your commits into either a single commit or a logical division of commits would be appreciated.

bjorn3 · 2024-09-21T15:51:16Z

walker.py

Where is this file used?

It searches for symbols to identify .c files and other files that use symbols that cannot be used in WASM. It was useful for debugging, but can be eliminated.

wrapper_linker_clang.sh

bjorn3 · 2024-09-21T15:54:11Z

src/bootstrap/src/core/build_steps/llvm.rs

+            .define("CMAKE_CXX_COMPILER_TARGET", &wasi_target_llvm)
+            .define("CMAKE_C_FLAGS", format!("{wasi_sysroot} {wasi_cflags_llvm}"))
+            .define("CMAKE_CXX_FLAGS", format!("{wasi_sysroot} {wasi_cflags_llvm}"))
+            .define("CMAKE_EXE_LINKER_FLAGS", wasi_ldflags_llvm)


Isn't there a cmake toolchain file in the wasi-sdk that sets all these flags as necessary?

compiler/rustc_target/src/target_features.rs

compiler/rustc_llvm/build.rs

compiler/rustc_fs_util/src/lib.rs

comment.txt

wrapper_linker_clang.sh

bjorn3 · 2024-09-21T16:26:55Z

wrapper_linker_clang.sh

+    shift 2
+    continue
+  fi
+  if [[ $1 == "-Wl,--max-memory=1073741824" ]]; then


Should this just remove the -Wl, prefix? I was genuinely running out of memory without this argument. Wasm shared memories need to declare a maximum size and lld gives a very small size by default.

oligamiq · 2024-09-22T17:21:42Z

Since I was assuming version 15, there was a conflict.
rustc is quite lax in that area, so I'll modify it to directly add -lwasi-emulated-mman.

bjorn3 · 2024-09-22T17:25:51Z

You can drop the first three commits that are currently in this PR when rebasing on top of compile_rustc_for_wasm16.

oligamiq · 2024-09-22T17:29:03Z

I've shut down the work server, so I'll do it tomorrow. I'll give it a try.

bjorn3 · 2024-09-23T14:01:39Z

Looks like the first commit is still there. If you want I could do the rebase for you and if you enable the github option for this have me push it directly to your PR branch.

oligamiq · 2024-09-23T14:06:28Z

What is the 'first commit'?

bjorn3 · 2024-09-23T14:31:07Z

I'm referring to 295aca5. This commit originates from the compile_rustc_for_wasm15 branch of mine despite this PR now targetting the compile_rustc_for_wasm16 branch.

oligamiq · 2024-09-23T14:38:00Z

If we lose it, won't it cause the build to possibly fail or fail to compile on the cranelift backend?
Or are you talking about integrating commits?

oligamiq · 2024-09-23T14:44:11Z

Sorry. It makes me crazy because it already exists. I'll turn it off.

Add Message
I'm currently adding -lwasi-emulated-mman and trying to build from scratch, so I can't rebase right now. If it succeeds, I'll do it with the new commit. wrapper_linker_clang.sh should be gone.

oligamiq · 2024-09-23T15:47:17Z

I believe the work is complete.

compiler/rustc_target/src/spec/targets/wasm32_wasip1_threads.rs

bjorn3 · 2024-09-23T17:13:03Z

It seems like it still isn't rebased on top of the compile_rustc_for_wasm16 branch. I've got it rebased locally and am currently building it to try it out. If you enable the option "Allow edits and access to secrets by maintainers" as explained by https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/allowing-changes-to-a-pull-request-branch-created-from-a-fork I can push my rebased version to this PR.

oligamiq · 2024-09-23T17:20:21Z

ok, understand. You want to create a new branch from wasm16 and cherry-pick it. I've given you the permissions for now, so please take care of it this time.

I thought github would do it automatically...

bjorn3 · 2024-09-23T17:38:36Z

Pushed

I thought github would do it automatically...

I think github preserves your choice, so if you ever disabled it, it will be kept disabled for all future PR's by default.

oligamiq · 2024-09-23T17:45:14Z

No, I thought I could just apply the changes to the commit in a nice way regardless of the top of branch.

bjorn3 · 2024-09-23T17:50:23Z

There were some conflicts between the top of the branch and your commits, so it wouldn't have been possible to merge until those conflicts were resolved. I resolved them for you while rebasing.

bjorn3 · 2024-09-23T18:41:27Z

I'm getting the following locally when building LLVM:

/home/bjorn/Projects/rust/src/llvm-project/llvm/include/llvm/ADT/bit.h:52:10: fatal error: 'machine/endian.h' file not found
   52 | #include <machine/endian.h>
      |          ^~~~~~~~~~~~~~~~~~

Edit: Messed up the llvm-project submodule while I did the rebase.

oligamiq · 2024-09-23T18:52:10Z

I believe there was a .define("HAVE_DLOPEN", ""); followed by a .define to turn it OFF.

I'll go look for it.

I have restored it, though,
https://github.com/oligamiq/rust/blob/compile_rustc_for_wasm15_dev_keep/src/bootstrap/src/core/build_steps/llvm.rs
Am I misremembering?

I understand, as I also had trouble with submodule changes.

oligamiq · 2024-09-24T14:18:03Z

about [Fix linking stdc++ on wasi]

config.llvm.toml:
It should work by simply setting up the wasi-sysroot, but it may not have worked correctly due to using version 24.

src/bootstrap/src/core/build_steps/compile.rs:
By upgrading the version of cc, linking for the WASI target should also function properly, and by setting the WASI_SYSROOT environment variable, linking to libc++.a should automatically occur. However, this might also be influenced by the use of version 24.
rust-lang/cc-rs#1114

bjorn3 · 2024-09-24T14:32:53Z

In this case the LLVM_STATIC_STDCPP env var ended up with just libstdc++.a instead of the full path, causing the rustc_llvm build script to produce an empty search path to find libstdc++.a in, which then results in rustc giving an error about the empty search path argument. I already have WASI_SYSROOT set.

This is really slow when producing a 156MB rustc.wasm output.

bjorn3 · 2024-09-24T16:16:46Z

I finally managed to get it to work locally. It does deadlock most of the time when running in wasmtime however unless I use RUST_LOG=trace. Maybe setting this slows down something just enough to avoid a deadlock even though it doesn't cause any additional output from wasmtime?

oligamiq · 2024-09-24T16:22:04Z

really?
This is what I copied during this pull request:
#7

It should have worked without any issues, but I will also test it with the copied version to ensure it works.
https://github.com/oligamiq/rust_wasm/tree/main/rustc_llvm

Add:
copy on rust_wasm is normal operation.
I will clone the repository, compile it, and check if it works correctly on this branch.

bjorn3 · 2024-09-24T17:11:35Z

Updating Wasmtime seems to have fixed the deadlocks.

oligamiq · 2024-09-24T17:12:39Z

oh...

bjorn3 · 2024-09-24T17:44:06Z

Checked that this PR doesn't break compiling cg_clif for single threaded wasm32-wasip1. I've spent enough time on this for today. I'm going to take another look at the changes tomorrow to see if anything is unnecessary or can be improved. After that I will merge this PR. Thanks again for working on this!

bjorn3 · 2024-09-24T18:43:47Z

This should be updated to use the https://github.com/YoWASP/llvm-project/releases/tag/rustc-2024-09-24-do-not-remove tag for the llvm-project submodule to ensure that it remains possible to build in the future.

…threads

oligamiq · 2024-09-25T13:39:50Z

I think LLVM_ENABLE_THREADS=OFF was broken

bjorn3 · 2024-09-25T13:42:58Z

Indeed. That commit was just a couple of changes that are necessary anyway to compile for wasm32-wasip1 once LLVM_ENABLE_THREADS=OFF gets fixed.

oligamiq · 2024-09-25T13:44:18Z

Also, RustCompiler have code to check if LLVM has multithreaded.

https://llvm.org/doxygen/group__LLVMCCoreThreading.html

bjorn3 requested changes Sep 21, 2024

View reviewed changes

oligamiq force-pushed the compile_rustc_for_wasm15_dev branch 4 times, most recently from 73bc239 to 881d67f Compare September 22, 2024 17:12

oligamiq changed the base branch from compile_rustc_for_wasm15 to compile_rustc_for_wasm16 September 22, 2024 17:13

oligamiq force-pushed the compile_rustc_for_wasm15_dev branch from 881d67f to 3fe3834 Compare September 23, 2024 05:32

oligamiq force-pushed the compile_rustc_for_wasm15_dev branch 2 times, most recently from d67fd0c to 1e6418a Compare September 23, 2024 15:41

bjorn3 reviewed Sep 23, 2024

View reviewed changes

compiler/rustc_target/src/spec/targets/wasm32_wasip1_threads.rs Outdated Show resolved Hide resolved

Compile rustc for wasm15 with llvm

d77d78b

bjorn3 force-pushed the compile_rustc_for_wasm15_dev branch from 578bd85 to d77d78b Compare September 23, 2024 17:38

Some fixes

6273b05

Fix llvm-project submodule

2e09141

Another fix

22ceada

bjorn3 force-pushed the compile_rustc_for_wasm15_dev branch from 3ab3533 to ed82c66 Compare September 24, 2024 14:33

Fix linking libc++ on wasi

ee85060

bjorn3 force-pushed the compile_rustc_for_wasm15_dev branch from ed82c66 to ee85060 Compare September 24, 2024 14:39

Disable linker optimizations for wasm

b05a1af

This is really slow when producing a 156MB rustc.wasm output.

bjorn3 changed the title ~~Compile rustc for wasm15 with llvm~~ Compile rustc+LLVM to wasm Sep 24, 2024

bjorn3 added 5 commits September 25, 2024 14:00

Better linking of libc++

094d63c

Faster LLVM compiles

51031c0

Remove some unnecessary configs

34b540e

Some preparation for once LLVM can compile for wasm32-wasip1 without …

b049100

…threads

Rustfmt

a2b402d

Simplify LLVM build code a bit

a3d0b4f

bjorn3 merged commit e19cccd into bjorn3:compile_rustc_for_wasm16 Sep 25, 2024
2 of 5 checks passed

This was referenced Sep 25, 2024

Compilation to WASM? rust-lang/miri#722

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Compile rustc+LLVM to wasm #6

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Compile rustc+LLVM to wasm #6

Compile rustc+LLVM to wasm #6

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