Many new wasm features are enabled if compile `wasm32v1-none` on LLVM 20+

[StackOverflowExcept1on]

Code

@alexcrichton

Code is minimized as much as possible and here is 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 new wasm features like reference-types, bulk-memory)
• wasm-program - this is smart contract that just allocates vector
• 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
cargo clean
./check.sh

   Compiling wasm-program v0.1.0 (/mnt/tmpfs/wasm-builder-regression/wasm-program)
   Compiling wasm-project v0.1.0 (/mnt/tmpfs/wasm-builder-regression/wasm-project)
    Finished `release` profile [optimized] target(s) in 0.27s
   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 1.67s
     Running `/mnt/tmpfs/wasm-builder-regression/wasm-checker/target/release/wasm-checker ./target/wasm32v1-none/release/wasm_program.wasm`
Error: UnknownOpcode(252)

opcode 252 is memory.fill (bulk memory operations)

wasm-dis ./target/wasm32v1-none/release/wasm_program.wasm

(module $wasm_program.wasm
 ...
 ;; custom section "producers", size 75
 ;; features section: mutable-globals, nontrapping-float-to-int, bulk-memory, sign-ext, reference-types, multivalue
)

target was wasm32v1-none, however here we see bunch of wasm features that shouldn't be here.

I've also added LLVM IR output so we can report this bug to LLVM as soon as possible:

ls ./target/wasm32v1-none/release/deps/*.ll

If I remove flag -C linker-plugin-lto, it works as expected

I expected to see this happen: I can use -C linker-plugin-lto to optimize my .wasm programs and it results in generating the correct code for the wasm32v1-none target

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

Version it worked on

Problems started after #135763. I don't have time to bisect exact version right now.

Version with regression

rustc +nightly-2025-04-22 --version --verbose:

rustc 1.88.0-nightly (d6c1e454a 2025-04-21)
binary: rustc
commit-hash: d6c1e454aa8af5e7e59fbf5c4e7d3128d2f99582
commit-date: 2025-04-21
host: x86_64-unknown-linux-gnu
release: 1.88.0-nightly
LLVM version: 20.1.2

[alexcrichton]

Given that you suspect this is an LLD issue due to the usage of linker-plugin-lto, could you minimize this to an invocation of wasm-ld and report to upstream LLVM?

[StackOverflowExcept1on]

@alexcrichton I'm having trouble reproducing this in LLVM:

llvm-as --version
wasm-tools --version

LLVM (http://llvm.org/):
  LLVM version 20.1.2
  Optimized build.
wasm-tools 1.229.0 (351f15374 2025-04-17)

llvm-as ./target/wasm32v1-none/release/deps/wasm_program.ll
wasm-ld ./target/wasm32v1-none/release/deps/wasm_program.bc -o ./target/wasm32v1-none/release/deps/wasm_program.wasm --no-entry --import-undefined --export init
wasm-tools validate -f=-bulk-memory ./target/wasm32v1-none/release/deps/wasm_program.wasm # ok
wasm-tools print ./target/wasm32v1-none/release/deps/wasm_program.wasm # prints wrong features

(module $wasm_program.wasm
  ...
  (@custom "target_features" (after code) "\08+\0bbulk-memory+\0fbulk-memory-opt+\16call-indirect-overlong+\0amultivalue+\0fmutable-globals+\13nontrapping-fptoint+\0freference-types+\08sign-ext")
)

[StackOverflowExcept1on]

It looks like there is some __wasm_init_memory symbol in the strat section:

  (start $__wasm_init_memory)
  (func $__wasm_init_memory (;1;) (type 1)
    i32.const 1048576
    i32.const 0
    i32.const 1
    memory.fill
  )

[StackOverflowExcept1on]

@alexcrichton situation has improved somewhat, but this does not completely resolve the issue.

git clone https://github.com/StackOverflowExcept1on/wasm-builder-regression.git
cd wasm-builder-regression/wasm-project
cargo clean
./check.sh # it works!
wasm-dis ./target/wasm32v1-none/release/wasm_program.wasm # but...

wasm-dis shows that LLVM still enables new features

 ;; custom section "producers", size 75
 ;; features section: mutable-globals, nontrapping-float-to-int, bulk-memory, sign-ext, reference-types, multivalue

Perhaps it would be beneficial to add assert to LLVM fork to ensure that the initial features mvp and mutable-globals have not been modified at end?

[alexcrichton]

Do you have reason to believe that this bug is something other than llvm/llvm-project#109443?