std: Introduce an unstable::stack module

This module will be used to manage the OS-specific TLS registers used to specify
the bounds of the current rust stack (useful in 1:1 and M:N)

src/libstd/rt/thread.rs

@@ -41,9 +41,9 @@ static DEFAULT_STACK_SIZE: libc::size_t = 1024 * 1024;
 // and invoke it.
 #[no_split_stack]
 extern fn thread_start(main: *libc::c_void) -> imp::rust_thread_return {
-    use rt::context;
+    use unstable::stack;
     unsafe {
-        context::record_stack_bounds(0, uint::max_value);
+        stack::record_stack_bounds(0, uint::max_value);
         let f: ~proc() = cast::transmute(main);
         (*f)();
         cast::transmute(0 as imp::rust_thread_return)

src/libstd/unstable/stack.rs

@@ -0,0 +1,274 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Rust stack-limit management
+//!
+//! Currently Rust uses a segmented-stack-like scheme in order to detect stack
+//! overflow for rust tasks. In this scheme, the prologue of all functions are
+//! preceded with a check to see whether the current stack limits are being
+//! exceeded.
+//!
+//! This module provides the functionality necessary in order to manage these
+//! stack limits (which are stored in platform-specific locations). The
+//! functions here are used at the borders of the task lifetime in order to
+//! manage these limits.
+//!
+//! This function is an unstable module because this scheme for stack overflow
+//! detection is not guaranteed to continue in the future. Usage of this module
+//! is discouraged unless absolutely necessary.
+
+use rt::task::Task;
+use option::None;
+use rt::local::Local;
+use unstable::intrinsics;
+
+static RED_ZONE: uint = 20 * 1024;
+
+/// This function is invoked from rust's current __morestack function. Segmented
+/// stacks are currently not enabled as segmented stacks, but rather one giant
+/// stack segment. This means that whenever we run out of stack, we want to
+/// truly consider it to be stack overflow rather than allocating a new stack.
+#[no_mangle]      // - this is called from C code
+#[no_split_stack] // - it would be sad for this function to trigger __morestack
+#[doc(hidden)]    // - Function must be `pub` to get exported, but it's
+                  //   irrelevant for documentation purposes.
+#[cfg(not(test))] // in testing, use the original libstd's version
+pub extern "C" fn rust_stack_exhausted() {
+
+    unsafe {
+        // We're calling this function because the stack just ran out. We need
+        // to call some other rust functions, but if we invoke the functions
+        // right now it'll just trigger this handler being called again. In
+        // order to alleviate this, we move the stack limit to be inside of the
+        // red zone that was allocated for exactly this reason.
+        let limit = get_sp_limit();
+        record_sp_limit(limit - RED_ZONE / 2);
+
+        // This probably isn't the best course of action. Ideally one would want
+        // to unwind the stack here instead of just aborting the entire process.
+        // This is a tricky problem, however. There's a few things which need to
+        // be considered:
+        //
+        //  1. We're here because of a stack overflow, yet unwinding will run
+        //     destructors and hence arbitrary code. What if that code overflows
+        //     the stack? One possibility is to use the above allocation of an
+        //     extra 10k to hope that we don't hit the limit, and if we do then
+        //     abort the whole program. Not the best, but kind of hard to deal
+        //     with unless we want to switch stacks.
+        //
+        //  2. LLVM will optimize functions based on whether they can unwind or
+        //     not. It will flag functions with 'nounwind' if it believes that
+        //     the function cannot trigger unwinding, but if we do unwind on
+        //     stack overflow then it means that we could unwind in any function
+        //     anywhere. We would have to make sure that LLVM only places the
+        //     nounwind flag on functions which don't call any other functions.
+        //
+        //  3. The function that overflowed may have owned arguments. These
+        //     arguments need to have their destructors run, but we haven't even
+        //     begun executing the function yet, so unwinding will not run the
+        //     any landing pads for these functions. If this is ignored, then
+        //     the arguments will just be leaked.
+        //
+        // Exactly what to do here is a very delicate topic, and is possibly
+        // still up in the air for what exactly to do. Some relevant issues:
+        //
+        //  #3555 - out-of-stack failure leaks arguments
+        //  #3695 - should there be a stack limit?
+        //  #9855 - possible strategies which could be taken
+        //  #9854 - unwinding on windows through __morestack has never worked
+        //  #2361 - possible implementation of not using landing pads
+
+        let mut task = Local::borrow(None::<Task>);
+        let n = task.get().name.as_ref()
+                    .map(|n| n.as_slice()).unwrap_or("<unnamed>");
+
+        // See the message below for why this is not emitted to the
+        // task's logger. This has the additional conundrum of the
+        // logger may not be initialized just yet, meaning that an FFI
+        // call would happen to initialized it (calling out to libuv),
+        // and the FFI call needs 2MB of stack when we just ran out.
+        println!("task '{}' has overflowed its stack", n);
+
+        intrinsics::abort();
+    }
+}
+
+#[inline(always)]
+pub unsafe fn record_stack_bounds(stack_lo: uint, stack_hi: uint) {
+    // When the old runtime had segmented stacks, it used a calculation that was
+    // "limit + RED_ZONE + FUDGE". The red zone was for things like dynamic
+    // symbol resolution, llvm function calls, etc. In theory this red zone
+    // value is 0, but it matters far less when we have gigantic stacks because
+    // we don't need to be so exact about our stack budget. The "fudge factor"
+    // was because LLVM doesn't emit a stack check for functions < 256 bytes in
+    // size. Again though, we have giant stacks, so we round all these
+    // calculations up to the nice round number of 20k.
+    record_sp_limit(stack_lo + RED_ZONE);
+
+    return target_record_stack_bounds(stack_lo, stack_hi);
+
+    #[cfg(not(windows))] #[cfg(not(target_arch = "x86_64"))] #[inline(always)]
+    unsafe fn target_record_stack_bounds(_stack_lo: uint, _stack_hi: uint) {}
+    #[cfg(windows, target_arch = "x86_64")] #[inline(always)]
+    unsafe fn target_record_stack_bounds(stack_lo: uint, stack_hi: uint) {
+        // Windows compiles C functions which may check the stack bounds. This
+        // means that if we want to perform valid FFI on windows, then we need
+        // to ensure that the stack bounds are what they truly are for this
+        // task. More info can be found at:
+        //   https://github.com/mozilla/rust/issues/3445#issuecomment-26114839
+        //
+        // stack range is at TIB: %gs:0x08 (top) and %gs:0x10 (bottom)
+        asm!("mov $0, %gs:0x08" :: "r"(stack_hi) :: "volatile");
+        asm!("mov $0, %gs:0x10" :: "r"(stack_lo) :: "volatile");
+    }
+}
+
+/// Records the current limit of the stack as specified by `end`.
+///
+/// This is stored in an OS-dependent location, likely inside of the thread
+/// local storage. The location that the limit is stored is a pre-ordained
+/// location because it's where LLVM has emitted code to check.
+///
+/// Note that this cannot be called under normal circumstances. This function is
+/// changing the stack limit, so upon returning any further function calls will
+/// possibly be triggering the morestack logic if you're not careful.
+///
+/// Also note that this and all of the inside functions are all flagged as
+/// "inline(always)" because they're messing around with the stack limits.  This
+/// would be unfortunate for the functions themselves to trigger a morestack
+/// invocation (if they were an actual function call).
+#[inline(always)]
+pub unsafe fn record_sp_limit(limit: uint) {
+    return target_record_sp_limit(limit);
+
+    // x86-64
+    #[cfg(target_arch = "x86_64", target_os = "macos")] #[inline(always)]
+    unsafe fn target_record_sp_limit(limit: uint) {
+        asm!("movq $$0x60+90*8, %rsi
+              movq $0, %gs:(%rsi)" :: "r"(limit) : "rsi" : "volatile")
+    }
+    #[cfg(target_arch = "x86_64", target_os = "linux")] #[inline(always)]
+    unsafe fn target_record_sp_limit(limit: uint) {
+        asm!("movq $0, %fs:112" :: "r"(limit) :: "volatile")
+    }
+    #[cfg(target_arch = "x86_64", target_os = "win32")] #[inline(always)]
+    unsafe fn target_record_sp_limit(limit: uint) {
+        // see: http://en.wikipedia.org/wiki/Win32_Thread_Information_Block
+        // store this inside of the "arbitrary data slot", but double the size
+        // because this is 64 bit instead of 32 bit
+        asm!("movq $0, %gs:0x28" :: "r"(limit) :: "volatile")
+    }
+    #[cfg(target_arch = "x86_64", target_os = "freebsd")] #[inline(always)]
+    unsafe fn target_record_sp_limit(limit: uint) {
+        asm!("movq $0, %fs:24" :: "r"(limit) :: "volatile")
+    }
+
+    // x86
+    #[cfg(target_arch = "x86", target_os = "macos")] #[inline(always)]
+    unsafe fn target_record_sp_limit(limit: uint) {
+        asm!("movl $$0x48+90*4, %eax
+              movl $0, %gs:(%eax)" :: "r"(limit) : "eax" : "volatile")
+    }
+    #[cfg(target_arch = "x86", target_os = "linux")]
+    #[cfg(target_arch = "x86", target_os = "freebsd")] #[inline(always)]
+    unsafe fn target_record_sp_limit(limit: uint) {
+        asm!("movl $0, %gs:48" :: "r"(limit) :: "volatile")
+    }
+    #[cfg(target_arch = "x86", target_os = "win32")] #[inline(always)]
+    unsafe fn target_record_sp_limit(limit: uint) {
+        // see: http://en.wikipedia.org/wiki/Win32_Thread_Information_Block
+        // store this inside of the "arbitrary data slot"
+        asm!("movl $0, %fs:0x14" :: "r"(limit) :: "volatile")
+    }
+
+    // mips, arm - Some brave soul can port these to inline asm, but it's over
+    //             my head personally
+    #[cfg(target_arch = "mips")]
+    #[cfg(target_arch = "arm")] #[inline(always)]
+    unsafe fn target_record_sp_limit(limit: uint) {
+        return record_sp_limit(limit as *c_void);
+        extern {
+            fn record_sp_limit(limit: *c_void);
+        }
+    }
+}
+
+/// The counterpart of the function above, this function will fetch the current
+/// stack limit stored in TLS.
+///
+/// Note that all of these functions are meant to be exact counterparts of their
+/// brethren above, except that the operands are reversed.
+///
+/// As with the setter, this function does not have a __morestack header and can
+/// therefore be called in a "we're out of stack" situation.
+#[inline(always)]
+pub unsafe fn get_sp_limit() -> uint {
+    return target_get_sp_limit();
+
+    // x86-64
+    #[cfg(target_arch = "x86_64", target_os = "macos")] #[inline(always)]
+    unsafe fn target_get_sp_limit() -> uint {
+        let limit;
+        asm!("movq $$0x60+90*8, %rsi
+              movq %gs:(%rsi), $0" : "=r"(limit) :: "rsi" : "volatile");
+        return limit;
+    }
+    #[cfg(target_arch = "x86_64", target_os = "linux")] #[inline(always)]
+    unsafe fn target_get_sp_limit() -> uint {
+        let limit;
+        asm!("movq %fs:112, $0" : "=r"(limit) ::: "volatile");
+        return limit;
+    }
+    #[cfg(target_arch = "x86_64", target_os = "win32")] #[inline(always)]
+    unsafe fn target_get_sp_limit() -> uint {
+        let limit;
+        asm!("movq %gs:0x28, $0" : "=r"(limit) ::: "volatile");
+        return limit;
+    }
+    #[cfg(target_arch = "x86_64", target_os = "freebsd")] #[inline(always)]
+    unsafe fn target_get_sp_limit() -> uint {
+        let limit;
+        asm!("movq %fs:24, $0" : "=r"(limit) ::: "volatile");
+        return limit;
+    }
+
+    // x86
+    #[cfg(target_arch = "x86", target_os = "macos")] #[inline(always)]
+    unsafe fn target_get_sp_limit() -> uint {
+        let limit;
+        asm!("movl $$0x48+90*4, %eax
+              movl %gs:(%eax), $0" : "=r"(limit) :: "eax" : "volatile");
+        return limit;
+    }
+    #[cfg(target_arch = "x86", target_os = "linux")]
+    #[cfg(target_arch = "x86", target_os = "freebsd")] #[inline(always)]
+    unsafe fn target_get_sp_limit() -> uint {
+        let limit;
+        asm!("movl %gs:48, $0" : "=r"(limit) ::: "volatile");
+        return limit;
+    }
+    #[cfg(target_arch = "x86", target_os = "win32")] #[inline(always)]
+    unsafe fn target_get_sp_limit() -> uint {
+        let limit;
+        asm!("movl %fs:0x14, $0" : "=r"(limit) ::: "volatile");
+        return limit;
+    }
+
+    // mips, arm - Some brave soul can port these to inline asm, but it's over
+    //             my head personally
+    #[cfg(target_arch = "mips")]
+    #[cfg(target_arch = "arm")] #[inline(always)]
+    unsafe fn target_get_sp_limit() -> uint {
+        return get_sp_limit() as uint;
+        extern {
+            fn get_sp_limit() -> *c_void;
+        }
+    }
+}