Attribute Macro naked

#[naked]

An attribute to define a function written entirely in assembly.

A naked function must contain only a single asm! statement: the contents of this asm! becomes the body of the function, with no prologue or epilogue. This means that the assembly code is responsible for including the necessary instructions to return from a function.

The primary use of naked function is to implement functions that use a custom calling convention that is not directly supported by rustc. Examples include hardware exception handlers, functions called from assembly code and customizing unwinding metadata.

Example

// The SYSV64 calling convention used on x86_64 Linux passes the first
// 2 integer arguments in EDI/ESI.
#[naked_function::naked]
pub unsafe extern "C" fn add(a: i32, b: i32) -> i32 {
    asm!(
        "lea eax, [edi + esi]",
        "ret",
    );
}

#[test]
fn main() {
    let ret = unsafe { add(1, 2) };
    assert_eq!(ret, 3);
}

asm! restrictions

The asm! is further restricted in that:

• Only sym and const operands are allowed.
• clobber_abi cannot be used.
• Only the raw and att_syntax options can be used.

These are the same set of operands accepted by global_asm!, which this attribute lowers the functions into.

Accessing function arguments.

The function signature is indicative only: it is merely there to allow Rust code to reference and call the naked function.

Function arguments cannot be referenced from the function body directly, instead you should access these from the expected register/stack slot as per the function ABI.

Similarly, you are responsible for placing function return values in the appropriate registers or stack slot for the calling convention used.

ABI and attributes

Naked functions must be marked as unsafe.

The function must have one of the following whitelisted ABIs:

• "C"
• "C-unwind"

Only the following attributes are supported on naked functions:

• #[export_name]
• #[no_mangle]
• #[link_section]
• #[cfg]
• #[doc] or /// doc comments