Consider removing useless -sign-ext flag in substrate-wasm-builder

[StackOverflowExcept1on]

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• This is not a support question.

Motivation

https://github.com/rust-lang/blog.rust-lang.org/blob/4a72d620768932213baf39b03c6f1e61c00cd038/posts/2024-08-26-webassembly-targets-change-in-default-target-features.md

Request

Should be removed here

polkadot-sdk/substrate/utils/wasm-builder/src/wasm_project.rs

Lines 836 to 842 in c8d5e5a

	let mut rustflags = String::new();
	match target {
	RuntimeTarget::Wasm => {
	rustflags.push_str(
	"-C target-cpu=mvp -C target-feature=-sign-ext -C link-arg=--export-table ",
	);
	},

Solution

No response

Are you willing to help with this request?

Maybe (please elaborate above)

[bkchr]

Do you have a little bit more context?

[StackOverflowExcept1on]

@bkchr Rust 1.82 (stable Oct 17) enables multi-value and reference-types by default. I think it makes sense to additionally disable these features.

[nazar-pc]

According to link you have provided -C target-cpu=mvp is already sufficient to disable all of these features, not sure why Substrate also has -C target-feature=-sign-ext given that same document explicitly mentions that it'll be disabled for mvp CPU.

[StackOverflowExcept1on]

Yep, maybe it make sense just leave -C target-cpu=mvp since Rust added more documentation about this stuff

[bkchr]

not sure why Substrate also has -C target-feature=-sign-ext given that same document explicitly mentions that it'll be disabled for mvp CPU.

Apparently it did not worked before: paritytech/substrate#13804 (comment)

AFAIR we also just disabled this feature because there were issues with our wasm parser and not because we didn't wanted this feature.

CC @koute

[StackOverflowExcept1on]

@bkchr @koute We could switch to the new target wasm32v1-none (it will be stabilized starting with Rust 1.84 and no more hacks with RUSTC_BOOTSTRAP=1) instead of wasm32-unknown-unknown.

[bkchr]

Sounds reasonable

[StackOverflowExcept1on]

@bkchr @koute I could do PR that would change the target to wasm32v1-none, but it doesn't have std as wasm32-unknown-unknown. Also, I don't fully understand why every runtime has this line:

polkadot-sdk/templates/minimal/runtime/src/lib.rs

Line 20 in bd2c35f

#![cfg_attr(not(feature = "std"), no_std)]

I.e. does this mean that the runtime requires std? In which cases does it use std and in which cases does it not?

[bkchr]

I.e. does this mean that the runtime requires std? In which cases does it use std and in which cases does it not?

No, the piece of code you have linked means that if std feature is not set, no_std is set to announce to rustc that std is not required.

I could do PR that would change the target to wasm32v1-none, but it doesn't have std as wasm32-unknown-unknown.

This would need to be done in a backwards compatible way, aka only do so if the new target exists.