move {get,set}_sp_limit into Rust-land

src/arch.rs

@@ -9,10 +9,6 @@ extern "C" {
   pub fn bootstrap();
   #[link_name = "lwt_swapcontext"]
   pub fn swapcontext(save: *mut Registers, restore: *mut Registers);
-  #[link_name = "lwt_get_sp_limit"]
-  pub fn get_sp_limit() -> *const u8;
-  #[link_name = "lwt_set_sp_limit"]
-  pub fn set_sp_limit(limit: *const u8);
   #[link_name = "lwt_abort"]
   pub fn abort() -> !;
 }
@@ -77,6 +73,22 @@ pub fn initialise_call_frame(stack: &mut Stack, init: uintptr_t, args: &[uintptr
   regs
 }
 
+// Rust stores a stack limit at [fs:0x70]. These two functions set and retrieve
+// the limit. They're marked as #[inline(always)] so that they can be used in
+// situations where the stack limit is invalid.
+
+#[inline(always)]
+pub unsafe fn get_sp_limit() -> *const u8 {
+  let limit;
+  asm!("movq %fs:0x70, $0" : "=r"(limit) ::: "volatile");
+  limit
+}
+
+#[inline(always)]
+pub unsafe fn set_sp_limit(limit: *const u8) {
+  asm!("movq $0, %fs:0x70" :: "r"(limit) :: "volatile");
+}
+
 #[inline]
 fn align_down_mut<T>(sp: *mut T, n: uint) -> *mut T {
   let sp = (sp as uint) & !(n - 1);

src/arch.s

@@ -91,22 +91,6 @@ lwt_bootstrap:
   mov r8, r15
   jmp rbx
 
-
-;; Rust stores a stack limit at [fs:0x70]. These two functions set and retrieve
-;; the limit. They could alternatively be implemented as #[inline(always)] Rust
-;; functions, with inline assembly, but I prefer keeping all the assembly-land
-;; stuff in here.
-
-global lwt_set_sp_limit
-lwt_set_sp_limit:
-  mov [fs:0x70], rdi
-  ret
-
-global lwt_get_sp_limit
-lwt_get_sp_limit:
-  mov rax, [fs:0x70]
-  ret
-
 global lwt_abort
 lwt_abort:
 ;; when a context is created for a native thread, it should only be switched

src/lib.rs

@@ -1,4 +1,4 @@
-#![feature(default_type_params, macro_rules, phase, globs)]
+#![feature(default_type_params, macro_rules, phase, globs, asm)]
 #![no_std]
 
 #[phase(plugin, link)]