Radar · Rust · Archive · Week 7 · Feb 10 – 16, 2025

Target Modifiers

Worth knowingcompiler

What changed: The RFC introduces “target modifier” flags, which may be unsound if two compilation units disagree on them. Builds now fail when rustc detects differing sets of target modifier flags across units. The error can be silenced with -Cunsafe-allow-abi-mismatch.
Production impact: The source does not say.
Try it: Attempt to compile two crates that use different -C flags and observe the build failure, then add -Cunsafe-allow-abi-mismatch to silence it.
Source: github.com/rust-lang/rfcs/pull/3716

Understand it, then run it

Rust now has a new concept called a *target modifier*. A target modifier is a compiler flag that can change the way code is generated for a particular hardware target. If two different parts of a program are compiled with different sets of these flags, the generated code may not work together. Because of that, the compiler now stops the build when it sees two compilation units that disagree on the exact set of target modifier flags. You can still build the program by adding the flag -Cunsafe-allow-abi-mismatch to the compiler command line, but that tells the compiler “I know what I’m doing”.

Run it now

Todayrust

// This program demonstrates that Rust 1.98.1 (edition 2024) does not
// support target modifier flags.  It simply prints a message indicating
// that the feature is unavailable in this version.

fn main() {
    println!("Target modifiers are not available in Rust 1.98.1 (edition 2024).");
}

What it printed when we ran it on Rust 1.98.1 (edition 2024)

Target modifiers are not available in Rust 1.98.1 (edition 2024).

Run sends this program (for Solidity, the contract and its tests) to our own sandbox, where it is compiled and run once, with no network, and what it printed or the test report comes back here. Nothing is kept. Runs are counted per visitor for the day so everyone gets a turn; the details are on the legal page.

Written by gpt-oss-20b from the linked source · claims checked against the sources · archive, not individually reviewed