rustc_driver: get rid of the extra thread

src/librustc_driver/lib.rs

@@ -24,6 +24,7 @@
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(set_stdio)]
+#![feature(rustc_stack_internals)]
 
 extern crate arena;
 extern crate getopts;
@@ -1461,16 +1462,56 @@ pub fn in_rustc_thread<F, R>(f: F) -> Result<R, Box<Any + Send>>
     // Temporarily have stack size set to 16MB to deal with nom-using crates failing
     const STACK_SIZE: usize = 16 * 1024 * 1024; // 16MB
 
-    let mut cfg = thread::Builder::new().name("rustc".to_string());
+    #[cfg(unix)]
+    let spawn_thread = unsafe {
+        // Fetch the current resource limits
+        let mut rlim = libc::rlimit {
+            rlim_cur: 0,
+            rlim_max: 0,
+        };
+        if libc::getrlimit(libc::RLIMIT_STACK, &mut rlim) != 0 {
+            let err = io::Error::last_os_error();
+            error!("in_rustc_thread: error calling getrlimit: {}", err);
+            true
+        } else if rlim.rlim_max < STACK_SIZE as libc::rlim_t {
+            true
+        } else {
+            std::rt::deinit_stack_guard();
+            rlim.rlim_cur = STACK_SIZE as libc::rlim_t;
+            if libc::setrlimit(libc::RLIMIT_STACK, &mut rlim) != 0 {
+                let err = io::Error::last_os_error();
+                // We have already deinited the stack. Further corruption is
+                // not allowed.
+                panic!("in_rustc_thread: error calling setrlimit: {}", err);
+            } else {
+                std::rt::update_stack_guard();
+                false
+            }
+        }
+    };
 
-    // FIXME: Hacks on hacks. If the env is trying to override the stack size
-    // then *don't* set it explicitly.
-    if env::var_os("RUST_MIN_STACK").is_none() {
-        cfg = cfg.stack_size(STACK_SIZE);
-    }
+    // We set the stack size at link time. See src/rustc/rustc.rs.
+    #[cfg(windows)]
+    let spawn_thread = false;
+
+    #[cfg(not(any(windows,unix)))]
+    let spawn_thread = true;
 
-    let thread = cfg.spawn(f);
-    thread.unwrap().join()
+    // The or condition is added from backward compatibility.
+    if spawn_thread || env::var_os("RUST_MIN_STACK").is_some() {
+        let mut cfg = thread::Builder::new().name("rustc".to_string());
+
+        // FIXME: Hacks on hacks. If the env is trying to override the stack size
+        // then *don't* set it explicitly.
+        if env::var_os("RUST_MIN_STACK").is_none() {
+            cfg = cfg.stack_size(STACK_SIZE);
+        }
+
+        let thread = cfg.spawn(f);
+        thread.unwrap().join()
+    } else {
+        Ok(f())
+    }
 }
 
 /// Get a list of extra command-line flags provided by the user, as strings.

src/libstd/rt.rs

@@ -73,3 +73,18 @@ fn lang_start<T: ::process::Termination + 'static>
 {
     lang_start_internal(&move || main().report(), argc, argv)
 }
+
+/// Function used for reverting changes to the main stack before setrlimit().
+/// This is POSIX (non-Linux) specific and unlikely to be directly stabilized.
+#[unstable(feature = "rustc_stack_internals", issue = "0")]
+pub unsafe fn deinit_stack_guard() {
+    ::sys::thread::guard::deinit();
+}
+
+/// Function used for resetting the main stack guard address after setrlimit().
+/// This is POSIX specific and unlikely to be directly stabilized.
+#[unstable(feature = "rustc_stack_internals", issue = "0")]
+pub unsafe fn update_stack_guard() {
+    let main_guard = ::sys::thread::guard::init();
+    ::sys_common::thread_info::reset_guard(main_guard);
+}

src/libstd/sys/unix/thread.rs

@@ -222,7 +222,7 @@ pub mod guard {
 #[cfg_attr(test, allow(dead_code))]
 pub mod guard {
     use libc;
-    use libc::mmap;
+    use libc::{mmap, munmap};
     use libc::{PROT_NONE, MAP_PRIVATE, MAP_ANON, MAP_FAILED, MAP_FIXED};
     use ops::Range;
     use sys::os;
@@ -336,6 +336,24 @@ pub mod guard {
         }
     }
 
+    pub unsafe fn deinit() {
+        if !cfg!(target_os = "linux") {
+            if let Some(mut stackaddr) = get_stack_start() {
+                // Ensure address is aligned. Same as above.
+                let remainder = (stackaddr as usize) % PAGE_SIZE;
+                if remainder != 0 {
+                    stackaddr = ((stackaddr as usize) + PAGE_SIZE - remainder)
+                        as *mut libc::c_void;
+                }
+
+                // Undo the guard page mapping.
+                if munmap(stackaddr, PAGE_SIZE) != 0 {
+                    panic!("unable to deallocate the guard page");
+                }
+            }
+        }
+    }
+
     #[cfg(any(target_os = "macos",
               target_os = "bitrig",
               target_os = "openbsd",

src/libstd/sys_common/thread_info.rs

@@ -50,3 +50,7 @@ pub fn set(stack_guard: Option<Guard>, thread: Thread) {
         thread,
     }));
 }
+
+pub fn reset_guard(stack_guard: Option<Guard>) {
+    THREAD_INFO.with(move |c| c.borrow_mut().as_mut().unwrap().stack_guard = stack_guard);
+}

src/rustc/rustc.rs

@@ -9,6 +9,15 @@
 // except according to those terms.
 
 #![feature(rustc_private)]
+#![feature(link_args)]
+
+// Set the stack size at link time on Windows. See rustc_driver::in_rustc_thread
+// for the rationale.
+#[cfg_attr(all(windows, target_env = "msvc"), link_args = "/STACK:16777216")]
+// We only build for msvc and gnu now, but we use a exhaustive condition here
+// so we can expect either the stack size to be set or the build fails.
+#[cfg_attr(all(windows, not(target_env = "msvc")), link_args = "-Wl,--stack,16777216")]
+extern {}
 
 extern crate rustc_driver;