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std: Introduce an unstable::stack module

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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)
This commit is contained in:
Alex Crichton 2013-12-12 17:20:03 -08:00
parent cab44fb076
commit 1815aea368
2 changed files with 276 additions and 2 deletions
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4
src/libstd/rt/thread.rs
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@ -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)

274
src/libstd/unstable/stack.rs Normal file
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@ -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;
}
}
}