Auto merge of #31684 - tmiasko:alternate-stack, r=alexcrichton

Remove alternate stack with sigaltstack before unmaping it.

Also reuse existing signal stack if already set, this is especially
useful when working with sanitizers that configure alternate stack
themselves.

This change depends on SS_DISABLE recently introduced in libc crate and updates
this git submodule accordingly.

src/liblibc

@@ -1 +1 @@
-Subproject commit a64ee24718c0289b82a77d692cf56f8a1226de51
+Subproject commit 403bdc88394919f297bdb365032044cc0481c319

src/libstd/sys/unix/stack_overflow.rs

@@ -46,7 +46,7 @@ mod imp {
     use super::Handler;
     use mem;
     use ptr;
-    use libc::{sigaltstack, SIGSTKSZ};
+    use libc::{sigaltstack, SIGSTKSZ, SS_DISABLE};
     use libc::{sigaction, SIGBUS, SIG_DFL,
                SA_SIGINFO, SA_ONSTACK, sighandler_t};
     use libc;
@@ -169,13 +169,32 @@ mod imp {
     }
 
     pub unsafe fn make_handler() -> Handler {
-        let stack = get_stack();
-        sigaltstack(&stack, ptr::null_mut());
-        Handler { _data: stack.ss_sp as *mut libc::c_void }
+        let mut stack = mem::zeroed();
+        sigaltstack(ptr::null(), &mut stack);
+        // Configure alternate signal stack, if one is not already set.
+        if stack.ss_flags & SS_DISABLE != 0 {
+            stack = get_stack();
+            sigaltstack(&stack, ptr::null_mut());
+            Handler { _data: stack.ss_sp as *mut libc::c_void }
+        } else {
+            Handler { _data: ptr::null_mut() }
+        }
     }
 
     pub unsafe fn drop_handler(handler: &mut Handler) {
-        munmap(handler._data, SIGSTKSZ);
+        if !handler._data.is_null() {
+            let stack =  libc::stack_t {
+                ss_sp: ptr::null_mut(),
+                ss_flags: SS_DISABLE,
+                // Workaround for bug in MacOS implementation of sigaltstack
+                // UNIX2003 which returns ENOMEM when disabling a stack while
+                // passing ss_size smaller than MINSIGSTKSZ. According to POSIX
+                // both ss_sp and ss_size should be ignored in this case.
+                ss_size: SIGSTKSZ,
+            };
+            sigaltstack(&stack, ptr::null_mut());
+            munmap(handler._data, SIGSTKSZ);
+        }
     }
 }
 

src/test/run-pass/signal-alternate-stack-cleanup.rs

@@ -0,0 +1,44 @@
+// Copyright 2016 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.
+
+// Previously memory for alternate signal stack have been unmapped during
+// main thread exit while still being in use by signal handlers. This test
+// triggers this situation by sending signal from atexit handler.
+//
+// ignore-windows
+
+#![feature(libc)]
+extern crate libc;
+
+use libc::*;
+
+unsafe extern fn signal_handler(signum: c_int, _: *mut siginfo_t, _: *mut c_void) {
+    assert_eq!(signum, SIGWINCH);
+}
+
+extern fn send_signal() {
+    unsafe {
+        raise(SIGWINCH);
+    }
+}
+
+fn main() {
+    unsafe {
+        // Install signal hander that runs on alternate signal stack.
+        let mut action: sigaction = std::mem::zeroed();
+        action.sa_flags = SA_SIGINFO | SA_ONSTACK;
+        action.sa_sigaction = signal_handler as sighandler_t;
+        sigaction(SIGWINCH, &action, std::ptr::null_mut());
+
+        // Send SIGWINCH on exit.
+        atexit(send_signal);
+    }
+}
+