Don't use core::intrinsics.

The core::intrinsics::unreachable() we used at the end of every naked
function is essentially pointless, as #[naked] implies that intrinsic
at the end of the function. rustc currently does not implement that
behavior (rust-lang/rust#32487), but it is a bug. On top of that,
anything except a single asm!() in naked functions is likely to be
disallowed in the future (rust-lang/rust#32490).

A nice side effect is that we avoid the core_intrinsics feature,
which will be never stabilized, though neither asm nor
naked_functions are likely to be stabilized soon.

Author: whitequark

src/arch/x86.rs

@@ -28,15 +28,14 @@
 //   after. A .cfi_def_* pseudoinstruction changes the CFA value similarly.
 // * Simulating return is as easy as restoring register values from the CFI table
 //   and then setting stack pointer to CFA.
-use core::intrinsics;
 use stack::Stack;
 
 #[derive(Debug)]
 pub struct StackPointer(*mut usize);
 
 pub unsafe fn init(stack: &Stack, f: unsafe extern "C" fn(usize) -> !) -> StackPointer {
   #[naked]
-  unsafe extern "C" fn init_trampoline_1() -> ! {
+  unsafe extern "C" fn init_trampoline_1() {
     asm!(
       r#"
         # gdb has a hardcoded check that rejects backtraces where frame addresses
@@ -60,12 +59,11 @@ pub unsafe fn init(stack: &Stack, f: unsafe extern "C" fn(usize) -> !) -> StackP
       .Lend:
       .size __morestack, .Lend-__morestack
       "#
-      : : "s" (init_trampoline_2 as usize) : "memory" : "volatile");
-    intrinsics::unreachable()
+      : : "s" (init_trampoline_2 as usize) : "memory" : "volatile")
   }
 
   #[naked]
-  unsafe extern "C" fn init_trampoline_2() -> ! {
+  unsafe extern "C" fn init_trampoline_2() {
     asm!(
       r#"
         # Set up the second part of our DWARF CFI.
@@ -78,8 +76,7 @@ pub unsafe fn init(stack: &Stack, f: unsafe extern "C" fn(usize) -> !) -> StackP
         # Call the provided function.
         call    *8(%esp)
       "#
-      : : : "memory" : "volatile");
-    intrinsics::unreachable()
+      : : : "memory" : "volatile")
   }
 
   unsafe fn push(sp: &mut StackPointer, val: usize) {
@@ -102,7 +99,7 @@ pub unsafe fn swap(arg: usize, old_sp: &mut StackPointer, new_sp: &StackPointer,
   let new_cfa = (new_stack.top() as *mut usize).offset(-1);
 
   #[naked]
-  unsafe extern "C" fn swap_trampoline() -> ! {
+  unsafe extern "C" fn swap_trampoline() {
     asm!(
       r#"
         # Save frame pointer explicitly; the unwinder uses it to find CFA of
@@ -125,8 +122,7 @@ pub unsafe fn swap(arg: usize, old_sp: &mut StackPointer, new_sp: &StackPointer,
         popl    %ebx
         jmpl    *%ebx
       "#
-      : : : "memory" : "volatile");
-    intrinsics::unreachable();
+      : : : "memory" : "volatile")
   }
 
   let ret: usize;

src/arch/x86_64.rs

@@ -32,15 +32,14 @@
 //   after. A .cfi_def_* pseudoinstruction changes the CFA value similarly.
 // * Simulating return is as easy as restoring register values from the CFI table
 //   and then setting stack pointer to CFA.
-use core::intrinsics;
 use stack::Stack;
 
 #[derive(Debug)]
 pub struct StackPointer(*mut usize);
 
 pub unsafe fn init(stack: &Stack, f: unsafe extern "C" fn(usize) -> !) -> StackPointer {
   #[naked]
-  unsafe extern "C" fn init_trampoline_1() -> ! {
+  unsafe extern "C" fn init_trampoline_1() {
     asm!(
       r#"
         # gdb has a hardcoded check that rejects backtraces where frame addresses
@@ -64,12 +63,11 @@ pub unsafe fn init(stack: &Stack, f: unsafe extern "C" fn(usize) -> !) -> StackP
       .Lend:
       .size __morestack, .Lend-__morestack
       "#
-      : : "s" (init_trampoline_2 as usize) : "memory" : "volatile");
-    intrinsics::unreachable()
+      : : "s" (init_trampoline_2 as usize) : "memory" : "volatile")
   }
 
   #[naked]
-  unsafe extern "C" fn init_trampoline_2() -> ! {
+  unsafe extern "C" fn init_trampoline_2() {
     asm!(
       r#"
         # Set up the second part of our DWARF CFI.
@@ -79,8 +77,7 @@ pub unsafe fn init(stack: &Stack, f: unsafe extern "C" fn(usize) -> !) -> StackP
         # Call the provided function.
         call    *8(%rsp)
       "#
-      : : : "memory" : "volatile");
-    intrinsics::unreachable()
+      : : : "memory" : "volatile")
   }
 
   unsafe fn push(sp: &mut StackPointer, val: usize) {
@@ -104,7 +101,7 @@ pub unsafe fn swap(arg: usize, old_sp: &mut StackPointer, new_sp: &StackPointer,
   let new_cfa = (new_stack.top() as *mut usize).offset(-1);
 
   #[naked]
-  unsafe extern "C" fn swap_trampoline() -> ! {
+  unsafe extern "C" fn swap_trampoline() {
     asm!(
       r#"
         # Save frame pointer explicitly; the unwinder uses it to find CFA of
@@ -127,8 +124,7 @@ pub unsafe fn swap(arg: usize, old_sp: &mut StackPointer, new_sp: &StackPointer,
         popq    %rbx
         jmpq    *%rbx
       "#
-      : : : "memory" : "volatile");
-    intrinsics::unreachable();
+      : : : "memory" : "volatile")
   }
 
   let ret: usize;

src/lib.rs

@@ -1,10 +1,8 @@
 // This file is part of libfringe, a low-level green threading library.
 // Copyright (c) Nathan Zadoks <[email protected]>
 // See the LICENSE file included in this distribution.
-#![feature(asm)]
+#![feature(asm, naked_functions)]
 #![cfg_attr(test, feature(test, thread_local, const_fn))]
-#![cfg_attr(target_arch = "x86",    feature(naked_functions, core_intrinsics))]
-#![cfg_attr(target_arch = "x86_64", feature(naked_functions, core_intrinsics))]
 #![no_std]
 
 //! libfringe is a library implementing safe, lightweight context switches,