Naked functions contain a trailing ret insn

[nagisa]

#[naked]
fn naked(){
    unsafe {
    asm!("ret");
    }
}

results in

; Function Attrs: naked uwtable
define internal void @_ZN5naked20hb8640283bf863d54eaaE() unnamed_addr #0 {
entry-block:
  call void asm "ret", "~{dirflag},~{fpsr},~{flags}"(), !srcloc !0
  ret void
}

    .section    .text._ZN5naked20hb8640283bf863d54eaaE,"ax",@progbits
    .align  16, 0x90
    .type   _ZN5naked20hb8640283bf863d54eaaE,@function
_ZN5naked20hb8640283bf863d54eaaE:
    .cfi_startproc
    #APP
    retq
    #NO_APP
    retq
.Lfunc_end0:
    .size   _ZN5naked20hb8640283bf863d54eaaE, .Lfunc_end0-_ZN5naked20hb8640283bf863d54eaaE
    .cfi_endproc

note the trailing retq instruction that shouldn’t otherwise be here.

An equivalent function compiled by clang looks like this:

; Function Attrs: naked noinline nounwind uwtable
define void @naked() #0 {
  call void asm sideeffect "ret", "~{dirflag},~{fpsr},~{flags}"() #1, !srcloc !1
  unreachable
}

    .globl  naked
    .align  16, 0x90
    .type   naked,@function
naked:                                  # @naked
    .cfi_startproc
# BB#0:
    #APP
    retq
    #NO_APP
.Lfunc_end0:
    .size   naked, .Lfunc_end0-naked
    .cfi_endproc

[nagisa]

cc @ticki

[ticki]

This is weird...

[nagisa]

cc #32408

[npmccallum]

@nagisa This is not a bug. You need to use the noreturn option. See: https://github.com/Amanieu/rfcs/blob/inline-asm/text/0000-inline-asm.md#options-1

@steveklabnik @Mark-Simulacrum This can be closed.

[steveklabnik]

Well, please note that when @nagisa wrote this, there was an entirely different asm implementation.

Checking today's nightly,

#![feature(naked_functions, asm)]

#[naked]
pub fn naked(){
    unsafe {
        asm!("ret");
    }
}

gives

playground::naked: # @playground::naked
# %bb.0:
	#APP
	retq
	#NO_APP
	retq

while

#![feature(naked_functions, asm)]

#[naked]
pub fn naked(){
    unsafe {
        asm!("ret", options(noreturn));
    }
}

gives

playground::naked: # @playground::naked
# %bb.0:
	#APP
	retq
	#NO_APP
	ud2

It does seem like the new impl has these semantics, and so yes, this isn't a bug. Thanks all!