Xous build failure due to naked_asm changes

[xobs]

Code

I tried this code:

$ RUST_COMPILER_RT_ROOT="$(pwd)/src/llvm-project/compiler-rt" RUSTFLAGS="-Zforce-unstable-if-unmarked=yes" cargo +nightly build --target riscv32imac-unknown-xous-elf -Zbinary-dep-depinfo --release --features "panic-unwind" --manifest-path "library/sysroot/Cargo.toml"

I expected to see this happen: Rust should build libstd for Xous

Instead, this happened: Rust errored out with could not compile 'unwinding':

   Compiling unwinding v0.2.4
   Compiling unwind v0.0.0 (/opt/Xous/rust-nightly/rust/library/unwind)
   Compiling panic_unwind v0.0.0 (/opt/Xous/rust-nightly/rust/library/panic_unwind)
error: <inline asm>:11:1: this directive must appear between .cfi_startproc and .cfi_endproc directives
.cfi_def_cfa_offset 0x90
^

error: could not compile `unwinding` (lib)

Version it worked on

It most recently worked on: Rust nightly 2024-12-11

Version with regression

rustc --version --verbose:

rustc 1.85.0-nightly (6d9f6ae36 2024-12-16)
binary: rustc
commit-hash: 6d9f6ae36ae1299d6126ba40c15191f7aa3b79d8
commit-date: 2024-12-16
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.5

More information

I have filed an issue in unwinding. This error likely appeared as a result of #128004. However, I am unable to merge PR 41 because CI is failing due to issue #80608.

@rustbot modify labels: +regression-from-stable-to-nightly -regression-untriaged

[xobs]

I've created this Issue because Xous is now unable to build. There are several factors at play:

• unwinding now fails on nightly due to codegen #[naked] functions using global asm #128004 requiring .cfi_startproc and .cfi_endproc on all functions
• unwinding depends on #[cfg(target_feature)] which doesn't work in --release mode on RISC-V
• It's unclear whether codegen #[naked] functions using global asm #128004 is a regression or working as-designed

[workingjubilee]

unwinding depends on #[cfg(target_feature)] which doesn't work in --release mode on RISC-V

hm. that should not be the case, to my knowledge? can you elaborate?

[xobs]

Sure.

#![feature(naked_functions)]

#[naked]
pub extern "C-unwind" fn example() {
    #[cfg(target_feature = "d")]
    unsafe {
        core::arch::naked_asm!("fsd fs0, 0x140(sp)");
    }
}

If you build this with cargo +nightly build --target riscv64gc-unknown-linux-gnu --release it fails with the following error:

error: <inline asm>:6:1: instruction requires the following: 'D' (Double-Precision Floating-Point)
fsd fs0, 0x140(sp)
^

Even though it's gated by the d flag that should only be active when the d target feature is present.