Completely rework fringe::Context and fringe::arch.

The new design concerns itself with one thing and exactly one thing:
passing values back and forth with an extern "C" function.
This allows to simplify fringe::arch into a single primitive, swap.

Close #21

Cargo.toml

@@ -15,9 +15,16 @@ optional = true
 git = "https://github.com/edef1c/libvalgrind"
 rev = "9ef793e9549aabfd2d969615180b69d29ce28d88"
 
-[dependencies.void]
-default-features = false
-version = "1"
+[dev-dependencies]
+simd = "0.1"
 
 [features]
 default = ["valgrind"]
+
+# These apply only to tests within this library; assembly at -O0 is completely
+# unreadable, so use -O1.
+[profile.dev]
+opt-level = 1
+
+[profile.test]
+opt-level = 1

README.md

@@ -44,17 +44,10 @@ git = "https://github.com/edef1c/libfringe.git"
 ### Feature flags
 
   [Cargo's feature flags]: http://doc.crates.io/manifest.html#the-[features]-section
-  libfringe provides several optional features through [Cargo's feature flags].
+  libfringe provides some optional features through [Cargo's feature flags].
   Currently, all of them are enabled by default.
 
 #### `valgrind`
 
   [Valgrind]: http://valgrind.org
   [Valgrind] integration. libfringe will register context stacks with Valgrind.
-
-#### `os`
-
-  [Built-in stack allocator]: https://edef1c.github.io/libfringe/fringe/struct.OsStack.html
-  [Built-in stack allocator] using your your operating system's anonymous memory mapping facility.
-  Currently only available for Unix.
-

benches/context_new.rs

@@ -1,41 +0,0 @@
-// This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
-// See the LICENSE file included in this distribution.
-#![feature(test)]
-extern crate test;
-extern crate fringe;
-use fringe::Context;
-
-static mut ctx_slot: *mut Context<'static, SliceStack<'static>> = 0 as *mut Context<_>;
-static mut stack_buf: [u8; 1024] = [0; 1024];
-
-#[bench]
-fn context_new(b: &mut test::Bencher) {
-  b.iter(|| unsafe {
-    let stack = SliceStack(&mut stack_buf);
-
-    let mut ctx = Context::new(stack, move || {
-      let ctx_ptr = ctx_slot;
-      loop {
-        Context::swap(ctx_ptr, ctx_ptr);
-      }
-    });
-
-    ctx_slot = &mut ctx;
-
-    Context::swap(ctx_slot, ctx_slot);
-  })
-}
-
-struct SliceStack<'a>(&'a mut [u8]);
-impl<'a> fringe::Stack for SliceStack<'a> {
-  fn top(&mut self) -> *mut u8 {
-    unsafe {
-      self.0.as_mut_ptr().offset(self.0.len() as isize)
-    }
-  }
-
-  fn limit(&self) -> *const u8 {
-    self.0.as_ptr()
-  }
-}

benches/swap.rs

@@ -1,31 +1,30 @@
 // This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
+// Copyright (c) edef <edef@edef.eu>,
+//               whitequark <whitequark@whitequark.org>
 // See the LICENSE file included in this distribution.
 #![feature(test)]
-#![cfg(feature = "os")]
 extern crate test;
 extern crate fringe;
+
 use fringe::Context;
 
-static mut ctx_slot: *mut Context<'static, fringe::OsStack> = 0 as *mut Context<_>;
+static mut ctx_slot: *mut Context<fringe::OsStack> = 0 as *mut Context<_>;
 
 #[bench]
 fn swap(b: &mut test::Bencher) {
+  unsafe extern "C" fn loopback(mut arg: usize) -> ! {
+    // This deliberately does not ignore arg, to measure the time it takes
+    // to move the return value between registers.
+    let ctx_ptr = ctx_slot;
+    loop { arg = Context::swap(ctx_ptr, ctx_ptr, arg) }
+  }
+
   unsafe {
     let stack = fringe::OsStack::new(4 << 20).unwrap();
-
-    let mut ctx = Context::new(stack, move || {
-      let ctx_ptr = ctx_slot;
-      loop {
-        Context::swap(ctx_ptr, ctx_ptr);
-      }
-    });
+    let mut ctx = Context::new(stack, loopback);
+    ctx_slot = &mut ctx;
 
     let ctx_ptr = &mut ctx;
-    ctx_slot = ctx_ptr;
-
-    Context::swap(ctx_ptr, ctx_ptr);
-
-    b.iter(|| Context::swap(ctx_ptr, ctx_ptr));
+    b.iter(|| Context::swap(ctx_ptr, ctx_ptr, 0));
   }
 }

benches/syscall.rs

@@ -4,11 +4,10 @@
 #![cfg(target_os = "linux")]
 #![feature(asm, test)]
 extern crate test;
-use test::Bencher;
 
 #[cfg(target_arch = "x86_64")]
 #[bench]
-fn kernel_swap(b: &mut Bencher) {
+fn syscall(b: &mut test::Bencher) {
   b.iter(|| unsafe {
     asm!("movq $$102, %rax\n\
           syscall"
@@ -21,7 +20,7 @@ fn kernel_swap(b: &mut Bencher) {
 
 #[cfg(target_arch = "x86")]
 #[bench]
-fn kernel_swap(b: &mut Bencher) {
+fn syscall(b: &mut test::Bencher) {
   b.iter(|| unsafe {
     asm!("mov $$24, %eax\n\
           int $$0x80"

src/arch/common.rs

@@ -1,34 +0,0 @@
-// This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
-// See the LICENSE file included in this distribution.
-use core::mem::{size_of, align_of};
-use core::cmp::max;
-use core::ptr;
-
-use void::{self, Void};
-
-use super::imp::STACK_ALIGN;
-
-pub unsafe extern "C" fn rust_trampoline<F>(f: *const F) -> !
-  where F: FnOnce() -> Void {
-  void::unreachable(ptr::read(f)())
-}
-
-pub unsafe fn push<T>(spp: &mut *mut usize, value: T) -> *mut T {
-  let mut sp = *spp as *mut T;
-  sp = offset_mut(sp, -1);
-  sp = align_down_mut(sp, max(align_of::<T>(), STACK_ALIGN));
-  ptr::write(sp, value); // does not attempt to drop old value
-  *spp = sp as *mut usize;
-  sp
-}
-
-pub fn align_down_mut<T>(sp: *mut T, n: usize) -> *mut T {
-  let sp = (sp as usize) & !(n - 1);
-  sp as *mut T
-}
-
-// ptr::offset_mut is positive ints only
-pub fn offset_mut<T>(ptr: *mut T, count: isize) -> *mut T {
-  (ptr as isize + count * (size_of::<T>() as isize)) as *mut T
-}

src/arch/mod.rs

@@ -1,16 +1,18 @@
 // This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
+// Copyright (c) edef <edef@edef.eu>,
+//               whitequark <whitequark@whitequark.org>
 // See the LICENSE file included in this distribution.
-pub use self::imp::Registers;
+pub use self::imp::*;
 
-unsafe impl Send for Registers {}
-
-mod common;
-
-#[cfg(target_arch = "x86_64")]
-#[path = "x86_64/mod.rs"]
-mod imp;
+// rust-lang/rust#25544
+// #[cfg_attr(target_arch = "x86",    path = "x86.rs")]
+// #[cfg_attr(target_arch = "x86_64", path = "x86_64.rs")]
+// mod imp;
 
 #[cfg(target_arch = "x86")]
-#[path = "x86/mod.rs"]
+#[path = "x86.rs"]
+mod imp;
+
+#[cfg(target_arch = "x86_64")]
+#[path = "x86_64.rs"]
 mod imp;

src/arch/x86.rs

@@ -0,0 +1,105 @@
+// This file is part of libfringe, a low-level green threading library.
+// Copyright (c) edef <edef@edef.eu>,
+//               whitequark <whitequark@whitequark.org>
+// See the LICENSE file included in this distribution.
+
+//! To understand the code in this file, keep in mind this fact:
+//! * i686 SysV C ABI requires the stack to be aligned at function entry,
+//!   so that `%esp+4` is a multiple of 16. Aligned operands are a requirement
+//!   of SIMD instructions, and making this the responsibility of the caller
+//!   avoids having to maintain a frame pointer, which is necessary when
+//!   a function has to realign the stack from an unknown state.
+//! * i686 SysV C ABI passes the first argument on the stack. This is
+//!   unfortunate, because unlike every other architecture we can't reuse
+//!   `swap` for the initial call, and so we use a trampoline.
+use stack::Stack;
+
+#[derive(Debug)]
+pub struct StackPointer(*mut usize);
+
+impl StackPointer {
+  unsafe fn new(stack: &Stack) -> StackPointer {
+    StackPointer(stack.top() as *mut usize)
+  }
+
+  unsafe fn push(&mut self, val: usize) {
+    self.0 = self.0.offset(-1);
+    *self.0 = val
+  }
+}
+
+pub unsafe fn init(stack: &Stack, f: unsafe extern "C" fn(usize) -> !) -> StackPointer {
+  let g: usize;
+  asm!(
+    r#"
+      # Push address of the trampoline.
+      call    1f
+
+      # Pop function.
+      popl    %ebx
+      # Push argument.
+      pushl   %eax
+      # Call it.
+      call    *%ebx
+
+    1:
+      # Pop address of the trampoline.
+      popl    %eax
+    "#
+    : "={eax}" (g)
+    :
+    : "memory"
+    : "volatile"
+  );
+
+  let mut sp = StackPointer::new(stack);
+  sp.push(0); // alignment
+  sp.push(0); // alignment
+  sp.push(0); // alignment
+  sp.push(f as usize); // function
+  sp.push(g as usize); // trampoline
+  sp
+}
+
+#[inline(always)]
+pub unsafe fn swap(arg: usize, old_sp: &mut StackPointer, new_sp: &StackPointer) -> usize {
+  let ret: usize;
+  asm!(
+    r#"
+      # Save frame pointer explicitly; LLVM doesn't spill it even if it is
+      # marked as clobbered.
+      pushl   %ebp
+      # Push instruction pointer of the old context and switch to
+      # the new context.
+      call    1f
+      # Restore frame pointer.
+      popl    %ebp
+      # Continue executing old context.
+      jmp     2f
+
+    1:
+      # Remember stack pointer of the old context, in case %rdx==%rsi.
+      movl    %esp, %ebx
+      # Load stack pointer of the new context.
+      movl    (%edi), %esp
+      # Save stack pointer of the old context.
+      movl    %ebx, (%esi)
+
+      # Pop instruction pointer of the new context (placed onto stack by
+      # the call above) and jump there; don't use `ret` to avoid return
+      # address mispredictions (~8ns on Ivy Bridge).
+      popl    %ebx
+      jmpl    *%ebx
+    2:
+    "#
+    : "={eax}" (ret)
+    : "{eax}" (arg)
+      "{esi}" (old_sp)
+      "{edi}" (new_sp)
+    : "eax",  "ebx",  "ecx",  "edx",  "esi",  "edi", //"ebp",  "esp",
+      "mmx0", "mmx1", "mmx2", "mmx3", "mmx4", "mmx5", "mmx6", "mmx7",
+      "xmm0", "xmm1", "xmm2", "xmm3", "xmm4", "xmm5", "xmm6", "xmm7",
+      "cc", "fpsr", "flags", "memory"
+    : "volatile");
+  ret
+}

src/arch/x86/.syntastic_asm_config

@@ -1 +0,0 @@
---32

src/arch/x86/init.s

@@ -1,40 +0,0 @@
-// This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
-// See the LICENSE file included in this distribution.
-
-//! initialise a new context
-//! arguments:
-//!  * eax: stack pointer
-//!  * ebx: function pointer
-//!  * ecx: data pointer
-//!
-//! return values:
-//!  * eax: new stack pointer
-
-// switch to the fresh stack
-xchg %esp, %eax
-
-// save the data pointer and the function pointer, respectively
-pushl %ecx
-pushl %ebx
-
-// save the return address, control flow continues at label 1
-call 1f
-// we arrive here once this context is reactivated (see swap.s)
-
-// restore the function pointer (the data pointer is the first argument, which lives at the top of the stack)
-popl %eax
-
-// initialise the frame pointer
-movl $$0, %ebp
-
-// call the function pointer with the data pointer (top of the stack is the first argument)
-call *%eax
-
-// crash if it ever returns
-ud2
-
-1:
-  // save our neatly-setup new stack
-  xchg %esp, %eax
-  // back into Rust-land we go

src/arch/x86/mod.rs

@@ -1,33 +0,0 @@
-// This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
-// See the LICENSE file included in this distribution.
-pub use self::common::*;
-
-macro_rules! init {
-  ($sp:expr, $f_ptr:expr, $tramp:expr) => {
-    asm!(include_str!("x86/init.s")
-         : "={eax}"($sp)
-         : "{eax}" ($sp),
-           "{ebx}" ($tramp),
-           "{ecx}" ($f_ptr)
-         :
-         : "volatile")
-  };
-}
-
-macro_rules! swap {
-  ($out_spp:expr, $in_spp:expr) => {
-    asm!(include_str!("x86/swap.s")
-         :
-         : "{eax}" ($out_spp),
-           "{ebx}" ($in_spp)
-         : "eax",  "ebx",  "ecx",  "edx",  "esi",  "edi", //"ebp",  "esp",
-           "mmx0", "mmx1", "mmx2", "mmx3", "mmx4", "mmx5", "mmx6", "mmx7",
-           "xmm0", "xmm1", "xmm2", "xmm3", "xmm4", "xmm5", "xmm6", "xmm7",
-           "cc", "fpsr", "eflags"
-         : "volatile")
-  };
-}
-
-#[path = "../x86_common.rs"]
-mod common;

src/arch/x86/swap.s

@@ -1,37 +0,0 @@
-// This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
-// See the LICENSE file included in this distribution.
-
-//! switch to a new context
-//! arguments:
-//!  * eax: stack pointer out pointer
-//!  * ebx: stack pointer in pointer
-
-// save the frame pointer
-pushl %ebp
-
-// save the return address to the stack, control flow continues at label 1
-call 1f
-// we arrive here once this context is reactivated
-
-// restore the frame pointer
-popl %ebp
-
-// and we merrily go on our way, back into Rust-land
-jmp 2f
-
-1:
-  // retrieve the new stack pointer
-  movl (%eax), %edx
-  // save the old stack pointer
-  movl %esp, (%ebx)
-  // switch to the new stack pointer
-  movl %edx, %esp
-
-  // jump into the new context (return to the call point)
-  // doing this instead of a straight `ret` is 8ns slower,
-  // presumably because the branch predictor tries to be clever about it
-  popl %eax
-  jmpl *%eax
-
-2:

src/arch/x86_64.rs

@@ -0,0 +1,92 @@
+// This file is part of libfringe, a low-level green threading library.
+// Copyright (c) edef <edef@edef.eu>,
+//               whitequark <whitequark@whitequark.org>
+// See the LICENSE file included in this distribution.
+
+//! To understand the code in this file, keep in mind these two facts:
+//! * x86_64 SysV C ABI has a "red zone": 128 bytes under the top of the stack
+//!   that is defined to be unmolested by signal handlers, interrupts, etc.
+//!   Leaf functions can use the red zone without adjusting rsp or rbp.
+//! * x86_64 SysV C ABI requires the stack to be aligned at function entry,
+//!   so that (%rsp+8) is a multiple of 16. Aligned operands are a requirement
+//!   of SIMD instructions, and making this the responsibility of the caller
+//!   avoids having to maintain a frame pointer, which is necessary when
+//!   a function has to realign the stack from an unknown state.
+//! * x86_64 SysV C ABI passes the first argument in %rdi. We also use %rdi
+//!   to pass a value while swapping context; this is an arbitrary choice
+//!   (we clobber all registers and could use any of them) but this allows us
+//!   to reuse the swap function to perform the initial call.
+
+use stack::Stack;
+
+#[derive(Debug)]
+pub struct StackPointer(*mut usize);
+
+impl StackPointer {
+  unsafe fn new(stack: &Stack) -> StackPointer {
+    StackPointer(stack.top() as *mut usize)
+  }
+
+  unsafe fn push(&mut self, val: usize) {
+    self.0 = self.0.offset(-1);
+    *self.0 = val
+  }
+}
+
+pub unsafe fn init(stack: &Stack, f: unsafe extern "C" fn(usize) -> !) -> StackPointer {
+  let mut sp = StackPointer::new(stack);
+  sp.push(0); // alignment
+  sp.push(f as usize);
+  sp
+}
+
+#[inline(always)]
+pub unsafe fn swap(arg: usize, old_sp: &mut StackPointer, new_sp: &StackPointer) -> usize {
+  let ret: usize;
+  asm!(
+    r#"
+      # Save frame pointer explicitly; LLVM doesn't spill it even if it is
+      # marked as clobbered.
+      pushq   %rbp
+      # Push instruction pointer of the old context and switch to
+      # the new context.
+      call    1f
+      # Restore frame pointer.
+      popq    %rbp
+      # Continue executing old context.
+      jmp     2f
+
+    1:
+      # Remember stack pointer of the old context, in case %rdx==%rsi.
+      movq    %rsp, %rax
+      # Load stack pointer of the new context.
+      movq    (%rdx), %rsp
+      # Save stack pointer of the old context.
+      movq    %rax, (%rsi)
+
+      # Pop instruction pointer of the new context (placed onto stack by
+      # the call above) and jump there; don't use `ret` to avoid return
+      # address mispredictions (~8ns on Ivy Bridge).
+      popq    %rax
+      jmpq    *%rax
+    2:
+    "#
+    : "={rdi}" (ret)
+    : "{rdi}" (arg)
+      "{rsi}" (old_sp)
+      "{rdx}" (new_sp)
+    : "rax",   "rbx",   "rcx",   "rdx",   "rsi",   "rdi", //"rbp",   "rsp",
+      "r8",    "r9",    "r10",   "r11",   "r12",   "r13",   "r14",   "r15",
+      "xmm0",  "xmm1",  "xmm2",  "xmm3",  "xmm4",  "xmm5",  "xmm6",  "xmm7",
+      "xmm8",  "xmm9",  "xmm10", "xmm11", "xmm12", "xmm13", "xmm14", "xmm15",
+      "xmm16", "xmm17", "xmm18", "xmm19", "xmm20", "xmm21", "xmm22", "xmm23",
+      "xmm24", "xmm25", "xmm26", "xmm27", "xmm28", "xmm29", "xmm30", "xmm31"
+      "cc", "fpsr", "flags", "memory"
+      // Ideally, we would set the LLVM "noredzone" attribute on this function
+      // (and it would be propagated to the call site). Unfortunately, rustc
+      // provides no such functionality. Fortunately, by a lucky coincidence,
+      // the "alignstack" LLVM inline assembly option does exactly the same
+      // thing on x86_64.
+    : "volatile", "alignstack");
+  ret
+}

src/arch/x86_64/.syntastic_asm_config

@@ -1 +0,0 @@
---64

src/arch/x86_64/init.s

@@ -1,41 +0,0 @@
-// This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
-// See the LICENSE file included in this distribution.
-
-//! initialise a new context
-//! arguments:
-//!  * rdi: stack pointer
-//!  * rsi: function pointer
-//!  * rdx: data pointer
-//!
-//! return values:
-//!  * rdi: new stack pointer
-
-// switch to the fresh stack
-xchg %rsp, %rdi
-
-// save the function pointer the data pointer, respectively
-pushq %rsi
-pushq %rdx
-
-// save the return address, control flow continues at label 1
-call 1f
-// we arrive here once this context is reactivated (see swap.s)
-
-// restore the data pointer and the function pointer, respectively
-popq %rdi
-popq %rax
-
-// initialise the frame pointer
-movq $$0, %rbp
-
-// call the function pointer with the data pointer (rdi is the first argument)
-call *%rax
-
-// crash if it ever returns
-ud2
-
-1:
-  // save our neatly-setup new stack
-  xchg %rsp, %rdi
-  // back into Rust-land we go

src/arch/x86_64/mod.rs

@@ -1,36 +0,0 @@
-// This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
-// See the LICENSE file included in this distribution.
-pub use self::common::*;
-
-macro_rules! init {
-  ($sp:expr, $f_ptr:expr, $tramp:expr) => {
-    asm!(include_str!("x86_64/init.s")
-         : "={rdi}"($sp)
-         : "{rdi}" ($sp),
-           "{rsi}" ($tramp),
-           "{rdx}" ($f_ptr)
-         :
-         : "volatile");
-  }
-}
-
-macro_rules! swap {
-  ($out_spp:expr, $in_spp:expr) => {
-    asm!(include_str!("x86_64/swap.s")
-         :
-         : "{rdi}" ($out_spp)
-           "{rsi}" ($in_spp)
-         : "rax",   "rbx",   "rcx",   "rdx",   "rsi",   "rdi", //"rbp",   "rsp",
-           "r8",    "r9",    "r10",   "r11",   "r12",   "r13",   "r14",   "r15",
-           "xmm0",  "xmm1",  "xmm2",  "xmm3",  "xmm4",  "xmm5",  "xmm6",  "xmm7",
-           "xmm8",  "xmm9",  "xmm10", "xmm11", "xmm12", "xmm13", "xmm14", "xmm15",
-           "xmm16", "xmm17", "xmm18", "xmm19", "xmm20", "xmm21", "xmm22", "xmm23",
-           "xmm24", "xmm25", "xmm26", "xmm27", "xmm28", "xmm29", "xmm30", "xmm31"
-           "cc", "fpsr", "eflags"
-         : "volatile");
-  }
-}
-
-#[path = "../x86_common.rs"]
-mod common;

src/arch/x86_64/swap.s

@@ -1,44 +0,0 @@
-// This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
-// See the LICENSE file included in this distribution.
-
-//! switch to a new context
-//! arguments:
-//!  * rdi: stack pointer out pointer
-//!  * rsi: stack pointer in pointer
-
-// make sure we leave the red zone alone
-sub $$128, %rsp
-
-// save the frame pointer
-pushq %rbp
-
-// save the return address to the stack, control flow continues at label 1
-call 1f
-// we arrive here once this context is reactivated
-
-// restore the frame pointer
-popq %rbp
-
-// give back the red zone
-add $$128, %rsp
-
-// and we merrily go on our way, back into Rust-land
-jmp 2f
-
-1:
-  // retrieve the new stack pointer
-  movq (%rsi), %rax
-  // save the old stack pointer
-  movq %rsp, (%rdi)
-  // switch to the new stack pointer
-  movq %rax, %rsp
-
-  // jump into the new context (return to the call point)
-  // doing this instead of a straight `ret` is 8ns faster,
-  // presumably because the branch predictor tries
-  // to be clever about it otherwise
-  popq %rax
-  jmpq *%rax
-
-2:

src/arch/x86_common.rs

@@ -1,35 +0,0 @@
-// This file is part of libfringe, a low-level green threading library.
-// Copyright (c) 2015, edef <edef@edef.eu>
-// See the LICENSE file included in this distribution.
-use void::Void;
-
-use stack::Stack;
-use arch::common::{push, rust_trampoline};
-
-pub const STACK_ALIGN: usize = 16;
-
-#[derive(Debug)]
-pub struct Registers {
-  stack_pointer: *mut usize
-}
-
-impl Registers {
-  #[inline]
-  pub unsafe fn new<S, F>(stack: &mut S, f: F) -> Registers
-    where S: Stack, F: FnOnce() -> Void
-  {
-    let mut sp = stack.top() as *mut usize;
-    let f_ptr = push(&mut sp, f);
-
-    init!(sp, f_ptr, rust_trampoline::<F> as unsafe extern "C" fn(*const F) -> !);
-
-    Registers {
-      stack_pointer: sp,
-    }
-  }
-
-  #[inline(always)]
-  pub unsafe fn swap(out_regs: *mut Registers, in_regs: *const Registers) {
-    swap!(&mut (*out_regs).stack_pointer, &(*in_regs).stack_pointer);
-  }
-}

src/context.rs

@@ -1,13 +1,10 @@
 // This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
+// Copyright (c) edef <edef@edef.eu>,
+//               whitequark <whitequark@whitequark.org>
 // See the LICENSE file included in this distribution.
-use core::marker::PhantomData;
-
-use void::Void;
-
-use arch::Registers;
 use stack;
-use debug::StackId;
+use debug;
+use arch;
 
 /// Context is the heart of libfringe.
 /// A context represents a saved thread of execution, along with a stack.
@@ -17,44 +14,41 @@ use debug::StackId;
 /// Every operation is unsafe, because libfringe can't make any guarantees
 /// about the state of the context.
 #[derive(Debug)]
-pub struct Context<'a, Stack: stack::Stack> {
-  regs: Registers,
-  _stack_id: StackId,
+pub struct Context<Stack: stack::Stack> {
   stack:     Stack,
-  _ref: PhantomData<&'a ()>
+  stack_id:  debug::StackId,
+  stack_ptr: arch::StackPointer
 }
 
-unsafe impl<'a, Stack> Send for Context<'a, Stack>
+unsafe impl<Stack> Send for Context<Stack>
   where Stack: stack::Stack + Send {}
 
-impl<'a, Stack> Context<'a, Stack> where Stack: stack::Stack {
-  /// Create a new Context. When it is swapped into,
-  /// it will call the passed closure.
-  #[inline]
-  pub unsafe fn new<F>(mut stack: Stack, f: F) -> Context<'a, Stack>
-    where F: FnOnce() -> Void + Send + 'a {
-    let stack_id = StackId::register(&mut stack);
-    let regs = Registers::new(&mut stack, f);
+impl<Stack> Context<Stack> where Stack: stack::Stack {
+  /// Create a new Context. When it is swapped into, it will call
+  /// `f(arg)`, where `arg` is the argument passed to `swap`.
+  pub unsafe fn new(stack: Stack, f: unsafe extern "C" fn(usize) -> !) -> Context<Stack> {
+    let stack_id  = debug::StackId::register(&stack);
+    let stack_ptr = arch::init(&stack, f);
     Context {
-      regs: regs,
-      _stack_id: stack_id,
       stack:     stack,
-      _ref: PhantomData
+      stack_id:  stack_id,
+      stack_ptr: stack_ptr
     }
   }
 
   /// Unwrap the context, returning the stack it contained.
-  #[inline]
   pub unsafe fn unwrap(self) -> Stack {
     self.stack
   }
 }
 
-impl<'i, InStack> Context<'i, InStack> where InStack: stack::Stack {
+impl<OldStack> Context<OldStack> where OldStack: stack::Stack {
   /// Switch to in_ctx, saving the current thread of execution to out_ctx.
   #[inline(always)]
-  pub unsafe fn swap<'o, OutStack>(out_ctx: *mut Context<'o, OutStack>, in_ctx: *const Context<'i, InStack>)
-    where OutStack: stack::Stack {
-    Registers::swap(&mut (*out_ctx).regs, &(*in_ctx).regs)
+  pub unsafe fn swap<NewStack>(old_ctx: *mut Context<OldStack>,
+                               new_ctx: *const Context<NewStack>,
+                               arg: usize) -> usize
+      where NewStack: stack::Stack {
+    arch::swap(arg, &mut (*old_ctx).stack_ptr, &(*new_ctx).stack_ptr)
   }
 }

src/debug/mod.rs

@@ -14,7 +14,7 @@ mod imp {
   pub struct StackId;
   /// No-op since no valgrind
   impl StackId {
-    pub fn register<Stack: stack::Stack>(_stack: &mut Stack) -> StackId {
+    pub fn register<Stack: stack::Stack>(_stack: &Stack) -> StackId {
       StackId
     }
   }

src/debug/valgrind.rs

@@ -11,7 +11,7 @@ pub struct StackId(self::valgrind::Value);
 
 impl StackId {
   #[inline(always)]
-  pub fn register<Stack: stack::Stack>(stack: &mut Stack) -> StackId {
+  pub fn register<Stack: stack::Stack>(stack: &Stack) -> StackId {
     StackId(stack_register(stack.limit(), stack.top()))
   }
 }

src/lib.rs

@@ -7,26 +7,17 @@
 //! libfringe is a low-level green threading library.
 //! It provides only a context-swapping mechanism.
 
-#[cfg(test)]
-#[macro_use]
-extern crate std;
-
-extern crate void;
-
 pub use context::Context;
 pub use stack::Stack;
 
-#[cfg(feature = "os")]
+#[cfg(any(unix, windows))]
 pub use os::Stack as OsStack;
 
 mod context;
 mod stack;
 
-#[cfg(feature = "os")]
+#[cfg(any(unix, windows))]
 mod os;
 
 mod arch;
 mod debug;
-
-#[cfg(not(test))]
-mod std { pub use core::*; }

src/os/mod.rs

@@ -47,13 +47,13 @@ impl Stack {
 }
 
 impl stack::Stack for Stack {
-  fn top(&mut self) -> *mut u8 {
+  fn top(&self) -> *mut u8 {
     unsafe {
       self.ptr.offset(self.len as isize)
     }
   }
 
-  fn limit(&self) -> *const u8 {
+  fn limit(&self) -> *mut u8 {
     unsafe {
       self.ptr.offset(sys::page_size() as isize)
     }

src/stack.rs

@@ -8,9 +8,9 @@ pub trait Stack {
   /// Returns the top of the stack.
   /// On all modern architectures, the stack grows downwards,
   /// so this is the highest address.
-  fn top(&mut self) -> *mut u8;
+  fn top(&self) -> *mut u8;
   /// Returns the bottom of the stack.
   /// On all modern architectures, the stack grows downwards,
   /// so this is the lowest address.
-  fn limit(&self) -> *const u8;
+  fn limit(&self) -> *mut u8;
 }

tests/basic.rs

@@ -1,26 +0,0 @@
-// This file is part of libfringe, a low-level green threading library.
-// Copyright (c) edef <edef@edef.eu>
-// See the LICENSE file included in this distribution.
-#![feature(thread_local)]
-extern crate fringe;
-use fringe::Context;
-
-#[thread_local]
-static mut ctx_slot: *mut Context<'static, fringe::OsStack> = 0 as *mut Context<_>;
-
-#[test]
-fn main() {
-  unsafe {
-    let stack = fringe::OsStack::new(4 << 20).unwrap();
-
-    let mut ctx = Context::new(stack, move || {
-      println!("it's alive!");
-      Context::swap(ctx_slot, ctx_slot);
-      panic!("Do not come back!")
-    });
-
-    ctx_slot = &mut ctx;
-
-    Context::swap(ctx_slot, ctx_slot);
-  }
-}

tests/context.rs

@@ -0,0 +1,60 @@
+// This file is part of libfringe, a low-level green threading library.
+// Copyright (c) edef <edef@edef.eu>,
+//               whitequark <whitequark@whitequark.org>
+// See the LICENSE file included in this distribution.
+#![feature(thread_local)]
+extern crate simd;
+extern crate fringe;
+
+use fringe::Context;
+
+#[thread_local]
+static mut ctx_slot: *mut Context<fringe::OsStack> = 0 as *mut Context<_>;
+
+#[test]
+fn context() {
+  unsafe extern "C" fn adder(arg: usize) -> ! {
+    println!("it's alive! arg: {}", arg);
+    let arg = Context::swap(ctx_slot, ctx_slot, arg + 1);
+    println!("still alive! arg: {}", arg);
+    Context::swap(ctx_slot, ctx_slot, arg + 1);
+    panic!("i should be dead");
+  }
+
+  unsafe {
+    let stack = fringe::OsStack::new(4 << 20).unwrap();
+    let mut ctx = Context::new(stack, adder);
+    ctx_slot = &mut ctx;
+
+    let ret = Context::swap(ctx_slot, ctx_slot, 10);
+    assert_eq!(ret, 11);
+    let ret = Context::swap(ctx_slot, ctx_slot, 50);
+    assert_eq!(ret, 51);
+  }
+}
+
+#[test]
+fn simd() {
+  unsafe extern "C" fn permuter(arg: usize) -> ! {
+    // This will crash if the stack is not aligned properly.
+    let x = simd::i32x4::splat(arg as i32);
+    let y = x * x;
+    println!("simd result: {:?}", y);
+    Context::swap(ctx_slot, ctx_slot, 0);
+    // And try again after a context switch.
+    let x = simd::i32x4::splat(arg as i32);
+    let y = x * x;
+    println!("simd result: {:?}", y);
+    Context::swap(ctx_slot, ctx_slot, 0);
+    panic!("i should be dead");
+  }
+
+  unsafe {
+    let stack = fringe::OsStack::new(4 << 20).unwrap();
+    let mut ctx = Context::new(stack, permuter);
+    ctx_slot = &mut ctx;
+
+    Context::swap(ctx_slot, ctx_slot, 10);
+    Context::swap(ctx_slot, ctx_slot, 20);
+  }
+}

tests/fpe.rs

@@ -12,7 +12,7 @@ use fringe::Context;
 use test::black_box;
 
 #[thread_local]
-static mut ctx_slot: *mut Context<'static, fringe::OsStack> = 0 as *mut Context<_>;
+static mut ctx_slot: *mut Context<fringe::OsStack> = 0 as *mut Context<_>;
 
 const FE_DIVBYZERO: i32 = 0x4;
 extern {
@@ -22,21 +22,20 @@ extern {
 #[test]
 #[ignore]
 fn fpe() {
-  unsafe {
-    let stack = fringe::OsStack::new(4 << 20).unwrap();
-
-    let mut ctx = Context::new(stack, move || {
-        println!("it's alive!");
+  unsafe extern "C" fn universe_destroyer(_arg: usize) -> ! {
     loop {
         println!("{:?}", 1.0/black_box(0.0));
-            Context::swap(ctx_slot, ctx_slot);
+        Context::swap(ctx_slot, ctx_slot, 0);
+    }
   }
-    });
 
+  unsafe {
+    let stack = fringe::OsStack::new(4 << 20).unwrap();
+    let mut ctx = Context::new(stack, universe_destroyer);
     ctx_slot = &mut ctx;
 
-    Context::swap(ctx_slot, ctx_slot);
+    Context::swap(ctx_slot, ctx_slot, 0);
     feenableexcept(FE_DIVBYZERO);
-    Context::swap(ctx_slot, ctx_slot);
+    Context::swap(ctx_slot, ctx_slot, 0);
   }
 }