326 lines
14 KiB
Rust
326 lines
14 KiB
Rust
// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Rust stack-limit management
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//!
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//! Currently Rust uses a segmented-stack-like scheme in order to detect stack
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//! overflow for rust tasks. In this scheme, the prologue of all functions are
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//! preceded with a check to see whether the current stack limits are being
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//! exceeded.
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//!
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//! This module provides the functionality necessary in order to manage these
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//! stack limits (which are stored in platform-specific locations). The
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//! functions here are used at the borders of the task lifetime in order to
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//! manage these limits.
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//!
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//! This function is an unstable module because this scheme for stack overflow
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//! detection is not guaranteed to continue in the future. Usage of this module
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//! is discouraged unless absolutely necessary.
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// iOS related notes
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//
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// It is possible to implement it using idea from
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// http://www.opensource.apple.com/source/Libc/Libc-825.40.1/pthreads/pthread_machdep.h
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//
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// In short: _pthread_{get,set}_specific_direct allows extremely fast
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// access, exactly what is required for segmented stack
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// There is a pool of reserved slots for Apple internal use (0..119)
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// First dynamic allocated pthread key starts with 257 (on iOS7)
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// So using slot 149 should be pretty safe ASSUMING space is reserved
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// for every key < first dynamic key
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//
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// There is also an opportunity to steal keys reserved for Garbage Collection
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// ranges 80..89 and 110..119, especially considering the fact Garbage Collection
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// never supposed to work on iOS. But as everybody knows it - there is a chance
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// that those slots will be re-used, like it happened with key 95 (moved from
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// JavaScriptCore to CoreText)
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//
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// Unfortunately Apple rejected patch to LLVM which generated
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// corresponding prolog, decision was taken to disable segmented
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// stack support on iOS.
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pub const RED_ZONE: uint = 20 * 1024;
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/// This function is invoked from rust's current __morestack function. Segmented
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/// stacks are currently not enabled as segmented stacks, but rather one giant
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/// stack segment. This means that whenever we run out of stack, we want to
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/// truly consider it to be stack overflow rather than allocating a new stack.
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#[cfg(not(test))] // in testing, use the original libstd's version
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#[lang = "stack_exhausted"]
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extern fn stack_exhausted() {
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use core::intrinsics;
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unsafe {
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// We're calling this function because the stack just ran out. We need
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// to call some other rust functions, but if we invoke the functions
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// right now it'll just trigger this handler being called again. In
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// order to alleviate this, we move the stack limit to be inside of the
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// red zone that was allocated for exactly this reason.
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let limit = get_sp_limit();
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record_sp_limit(limit - RED_ZONE / 2);
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// This probably isn't the best course of action. Ideally one would want
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// to unwind the stack here instead of just aborting the entire process.
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// This is a tricky problem, however. There's a few things which need to
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// be considered:
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//
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// 1. We're here because of a stack overflow, yet unwinding will run
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// destructors and hence arbitrary code. What if that code overflows
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// the stack? One possibility is to use the above allocation of an
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// extra 10k to hope that we don't hit the limit, and if we do then
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// abort the whole program. Not the best, but kind of hard to deal
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// with unless we want to switch stacks.
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//
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// 2. LLVM will optimize functions based on whether they can unwind or
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// not. It will flag functions with 'nounwind' if it believes that
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// the function cannot trigger unwinding, but if we do unwind on
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// stack overflow then it means that we could unwind in any function
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// anywhere. We would have to make sure that LLVM only places the
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// nounwind flag on functions which don't call any other functions.
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//
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// 3. The function that overflowed may have owned arguments. These
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// arguments need to have their destructors run, but we haven't even
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// begun executing the function yet, so unwinding will not run the
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// any landing pads for these functions. If this is ignored, then
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// the arguments will just be leaked.
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//
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// Exactly what to do here is a very delicate topic, and is possibly
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// still up in the air for what exactly to do. Some relevant issues:
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//
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// #3555 - out-of-stack failure leaks arguments
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// #3695 - should there be a stack limit?
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// #9855 - possible strategies which could be taken
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// #9854 - unwinding on windows through __morestack has never worked
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// #2361 - possible implementation of not using landing pads
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::stack_overflow::report();
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intrinsics::abort();
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}
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}
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// Windows maintains a record of upper and lower stack bounds in the Thread Information
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// Block (TIB), and some syscalls do check that addresses which are supposed to be in
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// the stack, indeed lie between these two values.
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// (See https://github.com/rust-lang/rust/issues/3445#issuecomment-26114839)
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//
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// When using Rust-managed stacks (libgreen), we must maintain these values accordingly.
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// For OS-managed stacks (libnative), we let the OS manage them for us.
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//
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// On all other platforms both variants behave identically.
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#[inline(always)]
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pub unsafe fn record_os_managed_stack_bounds(stack_lo: uint, _stack_hi: uint) {
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record_sp_limit(stack_lo + RED_ZONE);
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}
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#[inline(always)]
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pub unsafe fn record_rust_managed_stack_bounds(stack_lo: uint, stack_hi: uint) {
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// When the old runtime had segmented stacks, it used a calculation that was
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// "limit + RED_ZONE + FUDGE". The red zone was for things like dynamic
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// symbol resolution, llvm function calls, etc. In theory this red zone
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// value is 0, but it matters far less when we have gigantic stacks because
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// we don't need to be so exact about our stack budget. The "fudge factor"
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// was because LLVM doesn't emit a stack check for functions < 256 bytes in
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// size. Again though, we have giant stacks, so we round all these
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// calculations up to the nice round number of 20k.
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record_sp_limit(stack_lo + RED_ZONE);
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return target_record_stack_bounds(stack_lo, stack_hi);
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#[cfg(not(windows))] #[inline(always)]
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unsafe fn target_record_stack_bounds(_stack_lo: uint, _stack_hi: uint) {}
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#[cfg(all(windows, target_arch = "x86"))] #[inline(always)]
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unsafe fn target_record_stack_bounds(stack_lo: uint, stack_hi: uint) {
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// stack range is at TIB: %fs:0x04 (top) and %fs:0x08 (bottom)
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asm!("mov $0, %fs:0x04" :: "r"(stack_hi) :: "volatile");
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asm!("mov $0, %fs:0x08" :: "r"(stack_lo) :: "volatile");
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}
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#[cfg(all(windows, target_arch = "x86_64"))] #[inline(always)]
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unsafe fn target_record_stack_bounds(stack_lo: uint, stack_hi: uint) {
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// stack range is at TIB: %gs:0x08 (top) and %gs:0x10 (bottom)
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asm!("mov $0, %gs:0x08" :: "r"(stack_hi) :: "volatile");
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asm!("mov $0, %gs:0x10" :: "r"(stack_lo) :: "volatile");
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}
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}
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/// Records the current limit of the stack as specified by `end`.
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///
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/// This is stored in an OS-dependent location, likely inside of the thread
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/// local storage. The location that the limit is stored is a pre-ordained
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/// location because it's where LLVM has emitted code to check.
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///
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/// Note that this cannot be called under normal circumstances. This function is
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/// changing the stack limit, so upon returning any further function calls will
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/// possibly be triggering the morestack logic if you're not careful.
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///
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/// Also note that this and all of the inside functions are all flagged as
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/// "inline(always)" because they're messing around with the stack limits. This
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/// would be unfortunate for the functions themselves to trigger a morestack
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/// invocation (if they were an actual function call).
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#[inline(always)]
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pub unsafe fn record_sp_limit(limit: uint) {
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return target_record_sp_limit(limit);
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// x86-64
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#[cfg(all(target_arch = "x86_64",
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any(target_os = "macos", target_os = "ios")))]
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#[inline(always)]
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unsafe fn target_record_sp_limit(limit: uint) {
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asm!("movq $$0x60+90*8, %rsi
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movq $0, %gs:(%rsi)" :: "r"(limit) : "rsi" : "volatile")
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}
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#[cfg(all(target_arch = "x86_64", target_os = "linux"))] #[inline(always)]
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unsafe fn target_record_sp_limit(limit: uint) {
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asm!("movq $0, %fs:112" :: "r"(limit) :: "volatile")
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}
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#[cfg(all(target_arch = "x86_64", target_os = "windows"))] #[inline(always)]
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unsafe fn target_record_sp_limit(_: uint) {
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}
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#[cfg(all(target_arch = "x86_64", target_os = "freebsd"))] #[inline(always)]
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unsafe fn target_record_sp_limit(limit: uint) {
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asm!("movq $0, %fs:24" :: "r"(limit) :: "volatile")
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}
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#[cfg(all(target_arch = "x86_64", target_os = "dragonfly"))] #[inline(always)]
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unsafe fn target_record_sp_limit(limit: uint) {
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asm!("movq $0, %fs:32" :: "r"(limit) :: "volatile")
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}
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// x86
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#[cfg(all(target_arch = "x86",
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any(target_os = "macos", target_os = "ios")))]
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#[inline(always)]
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unsafe fn target_record_sp_limit(limit: uint) {
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asm!("movl $$0x48+90*4, %eax
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movl $0, %gs:(%eax)" :: "r"(limit) : "eax" : "volatile")
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}
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#[cfg(all(target_arch = "x86",
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any(target_os = "linux", target_os = "freebsd")))]
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#[inline(always)]
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unsafe fn target_record_sp_limit(limit: uint) {
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asm!("movl $0, %gs:48" :: "r"(limit) :: "volatile")
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}
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#[cfg(all(target_arch = "x86", target_os = "windows"))] #[inline(always)]
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unsafe fn target_record_sp_limit(_: uint) {
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}
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// mips, arm - Some brave soul can port these to inline asm, but it's over
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// my head personally
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#[cfg(any(target_arch = "mips",
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target_arch = "mipsel",
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all(target_arch = "arm", not(target_os = "ios"))))]
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#[inline(always)]
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unsafe fn target_record_sp_limit(limit: uint) {
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use libc::c_void;
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return record_sp_limit(limit as *const c_void);
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extern {
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fn record_sp_limit(limit: *const c_void);
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}
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}
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// iOS segmented stack is disabled for now, see related notes
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#[cfg(all(target_arch = "arm", target_os = "ios"))] #[inline(always)]
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unsafe fn target_record_sp_limit(_: uint) {
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}
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}
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/// The counterpart of the function above, this function will fetch the current
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/// stack limit stored in TLS.
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///
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/// Note that all of these functions are meant to be exact counterparts of their
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/// brethren above, except that the operands are reversed.
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///
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/// As with the setter, this function does not have a __morestack header and can
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/// therefore be called in a "we're out of stack" situation.
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#[inline(always)]
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pub unsafe fn get_sp_limit() -> uint {
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return target_get_sp_limit();
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// x86-64
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#[cfg(all(target_arch = "x86_64",
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any(target_os = "macos", target_os = "ios")))]
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#[inline(always)]
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unsafe fn target_get_sp_limit() -> uint {
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let limit;
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asm!("movq $$0x60+90*8, %rsi
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movq %gs:(%rsi), $0" : "=r"(limit) :: "rsi" : "volatile");
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return limit;
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}
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#[cfg(all(target_arch = "x86_64", target_os = "linux"))] #[inline(always)]
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unsafe fn target_get_sp_limit() -> uint {
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let limit;
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asm!("movq %fs:112, $0" : "=r"(limit) ::: "volatile");
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return limit;
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}
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#[cfg(all(target_arch = "x86_64", target_os = "windows"))] #[inline(always)]
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unsafe fn target_get_sp_limit() -> uint {
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return 1024;
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}
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#[cfg(all(target_arch = "x86_64", target_os = "freebsd"))] #[inline(always)]
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unsafe fn target_get_sp_limit() -> uint {
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let limit;
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asm!("movq %fs:24, $0" : "=r"(limit) ::: "volatile");
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return limit;
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}
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#[cfg(all(target_arch = "x86_64", target_os = "dragonfly"))] #[inline(always)]
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unsafe fn target_get_sp_limit() -> uint {
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let limit;
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asm!("movq %fs:32, $0" : "=r"(limit) ::: "volatile");
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return limit;
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}
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// x86
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#[cfg(all(target_arch = "x86",
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any(target_os = "macos", target_os = "ios")))]
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#[inline(always)]
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unsafe fn target_get_sp_limit() -> uint {
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let limit;
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asm!("movl $$0x48+90*4, %eax
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movl %gs:(%eax), $0" : "=r"(limit) :: "eax" : "volatile");
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return limit;
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}
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#[cfg(all(target_arch = "x86",
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any(target_os = "linux", target_os = "freebsd")))]
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#[inline(always)]
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unsafe fn target_get_sp_limit() -> uint {
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let limit;
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asm!("movl %gs:48, $0" : "=r"(limit) ::: "volatile");
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return limit;
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}
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#[cfg(all(target_arch = "x86", target_os = "windows"))] #[inline(always)]
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unsafe fn target_get_sp_limit() -> uint {
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return 1024;
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}
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// mips, arm - Some brave soul can port these to inline asm, but it's over
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// my head personally
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#[cfg(any(target_arch = "mips",
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target_arch = "mipsel",
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all(target_arch = "arm", not(target_os = "ios"))))]
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#[inline(always)]
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unsafe fn target_get_sp_limit() -> uint {
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use libc::c_void;
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return get_sp_limit() as uint;
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extern {
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fn get_sp_limit() -> *const c_void;
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}
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}
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// iOS doesn't support segmented stacks yet. This function might
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// be called by runtime though so it is unsafe to mark it as
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// unreachable, let's return a fixed constant.
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#[cfg(all(target_arch = "arm", target_os = "ios"))] #[inline(always)]
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unsafe fn target_get_sp_limit() -> uint {
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1024
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}
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}
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