All interrupt ABIs should enforce either `()` or `!` as return types

[workingjubilee]

I tried this code: Godbolt

I expected to see this happen: ...interrupts don't really return things, they're side effects, that's kind of in the definition, so these shouldn't return anything, and the ABI should enforce that, or during lowering..?

Instead, this happened:

rustc-LLVM ERROR: ISRs cannot return any value
rustc-LLVM ERROR: Functions with the interrupt attribute must have void return type!
rustc-LLVM ERROR: X86 interrupts may not return any value

msp430

#![feature(abi_msp430_interrupt)]

pub extern "msp430-interrupt" fn msp430_isr() -> u64 {
    9001u64
}

pub fn call() {
    let _ = msp430_isr();
}

riscv

#![feature(abi_riscv_interrupt)]
pub extern "riscv-interrupt-m" fn interrupt_machine() -> u64 {
    9001u64
}

pub extern "riscv-interrupt-s" fn interrupt_supervisor() -> u64 {
    9002u64
}

pub fn main() {
    let a = interrupt_machine();
    let b = interrupt_supervisor();
    println!("{}", a + b);
}

x86

#![feature(abi_x86_interrupt)]
pub extern "x86-interrupt" fn interrupt_machine() -> u64 {
    9001u64
}


pub fn main() {
    let a = interrupt_machine();
    println!("{}", a);
}

Meta

rustc --version --verbose:

rustc 1.84.0-nightly (a0d98ff0e 2024-10-31)
binary: rustc
commit-hash: a0d98ff0e5b6e1f2c63fd26f68484792621b235c
commit-date: 2024-10-31
host: x86_64-unknown-linux-gnu
release: 1.84.0-nightly
LLVM version: 19.1.1

@rustbot label: +A-ABI +A-hardware-interrupts +A-LLVM +F-abi_x86_interrupt +O-x86_64 +O-x86_32 +O-riscv +O-msp430 +T-compiler

Related Issues

• Tracking issue for the msp430-interrupt calling convention/ABI #38487
• Tracking issue for the x86-interrupt calling convention #40180
• Tracking Issue for riscv-interrupt-{m,s} ABIs #111889
• extern "x86-interrupt" fn allows absurd signatures #132835
• Directly calling extern "riscv-interrupt-{m,s}" fn... compiles? #132836
• Most extern "*-interrupt-*" fn should enforce 0-sized signatures #132837
• Directly calling "msp430-interrupt" fn should also be invalid #132839