Can not disable reference-types feature for wasm32 target with -C linker-plugin-lto flag

[StackOverflowExcept1on]

Code

@alexcrichton

Code is minimized as much as possible and here is a demo repository: https://github.com/StackOverflowExcept1on/wasm-builder-regression/

• wasm-checker - simple CLI tool that passes wasm to parity-wasm parser (it does not support reference-types)
• wasm-program - this is smart contract that panics and terminates with an error
• wasm-project - some intermediate directory that is generated by our utility
• check.sh source code

git clone https://github.com/StackOverflowExcept1on/wasm-builder-regression.git
cd wasm-builder-regression/wasm-project
./check.sh

    Finished `release` profile [optimized] target(s) in 8.30s

   Compiling gear-wasm v0.45.1
   Compiling wasm-checker v0.1.0 (/mnt/tmpfs/wasm-builder-regression/wasm-checker)
    Finished `release` profile [optimized] target(s) in 1.68s
     Running `/mnt/tmpfs/wasm-builder-regression/wasm-checker/target/release/wasm-checker ./target/wasm32-unknown-unknown/release/wasm_program.wasm`

Error: InvalidTableReference(128)

If I remove flag -C linker-plugin-lto, it works as described in #128511

I expected to see this happen: I can disable reference-types via -Ctarget-cpu=mvp and -Zbuild-std

Instead, this happened: there is some kind of conflict between compiler flags?

Version it worked on

It most recently worked on: nightly-2024-07-31

Version with regression

rustc +nightly-2024-08-01 --version --verbose:

rustc 1.82.0-nightly (28a58f2fa 2024-07-31)
binary: rustc
commit-hash: 28a58f2fa7f0c46b8fab8237c02471a915924fe5
commit-date: 2024-07-31
host: x86_64-unknown-linux-gnu
release: 1.82.0-nightly
LLVM version: 19.1.0

[alexcrichton]

Thanks for the report! I'm not actually sure what's going on here. My best guess though is that wasm-ld is performing codegen on behalf of -Clinker-plugin-lto and it's not configured the same way as rustc. For example -Ctarget-cpu is a Rust compiler flag which it translates to LLVM, but this isn't passed to wasm-ld. (AFAIK there's no way to pass this flag to wasm-ld).

The LLVM IR going into wasm-ld looks like it's correctly annotated with "target-cpu"="mvp" on functions which also perplexes me...

Put another way, you're doing everything right here, and the bug lies somewhere in the interaction of codegen in wasm-ld and configuring LLVM with features disabled. It might be a bug in wasm-ld itself or it might be a bug in rustc. A reduction of this issue is:

target triple = "wasm32-unknown-unknown"
target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-n32:64-S128-ni:1:10:20"

define void @foo(ptr %a) #0 {
  call void %a()
  ret void
}

attributes #0 = { nounwind "target-cpu"="mvp" }

Locally I see:

$ llvm-as wat.ll
$ wasm-ld wat.bc -o foo.wasm --no-entry --export foo 
$ wasm-tools validate -f=-reference-types foo.wasm
error: func 0 failed to validate

Caused by:
    0: zero byte expected (at offset 0x4b)

I've opened llvm/llvm-project#109443 to see if folks have thoughts there.

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-medium

[StackOverflowExcept1on]

@alexcrichton this bug is also reproduced on the new target wasm32v1-none.

[alexcrichton]

Can you provide reproduction steps necessary? Just saying "also reproduced on the new target" isn't too helpful at indicating what you're doing to reproduce this or what is even being reproduced.

[StackOverflowExcept1on]

@alexcrichton Of course, same example, but with different branch: https://github.com/StackOverflowExcept1on/wasm-builder-regression/tree/wasm32v1-none

git clone https://github.com/StackOverflowExcept1on/wasm-builder-regression.git --branch wasm32v1-none
cd wasm-builder-regression/wasm-project
./check.sh

[alexcrichton]

Oh, that's still the same bug at llvm/llvm-project#109443, which still hasn't been fixed.