# Linux Kernel compiler argment parameter

Some example https://godbolt.org/z/KKzhe8n38

define dso_local noundef i32 @f() 

local_unnamed_addr #0 {
  ret i32 42
}

define dso_local void @f(ptr dead_on_unwind noalias nocapture writable writeonly sret(%struct.S) align 4 %0) 

local_unnamed_addr #0 {
  store i32 42, ptr %0, align 4
  ret void
}

----

### rustc PRs for compiler flags:
- https://github.com/rust-lang/rust/pull/116892/files
- https://github.com/rust-lang/rust/pull/105812
- https://github.com/rust-lang/rust/pull/124655

### Good feeture to have (macros)

#### completed by https://rust-lang.zulipchat.com/#narrow/stream/404510-wg-macros/topic/May.20we.20need.20a.20.60c_stringify!.60.20and.20.60c_concat!.60.20macros.3F

- https://lore.kernel.org/rust-for-linux/CANiq72nbbtNp4vGGHkXVSgSW+WU=[e-mail]

# Rust4Linux issue [#355](https://github.com/Rust-for-Linux/linux/issues/355)

### Support for `-Zregparm=3` and `-Zreg-struct-return`.

These are two different feature, one is for the `-Zregparm` and the other one if for the `-Zreg-struct-return`.

There was already some initial exploration from Miguel for `-Zregparm`, and the tracking issue is https://github.com/rust-lang/rust/issues/116972

## (`-mregparm=3`) Rustc issue #[116972](https://github.com/rust-lang/rust/issues/116972) exploration

Looks like that there is a reference to the linux kernel that is https://github.com/intel-lab-lkp/linux/commit/366c4bda8d5890a8f44ec23a07664e1d77c5cada where they are explain the problem and a use case for this parameter.

TL;DR: The equivalent of Clang's/GCC's `-mregparm=3`. The kernel needs it to support the x86 32-bit architecture, together with `-Zreg-struct-return`.

Clang reference implementation: https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CodeGenModule.cpp#L451

## Rustc issue #[116973](https://github.com/rust-lang/rust/issues/116973) exploration

Still need to be done.