Auto merge of rust-lang#74006 - euclio:sys-unix-static-mut, r=oli-obk

libstd: remove some mutable statics in sys::unix

My understanding is that this achieves the same behavior and performance with safe code.

Author: bors

src/libstd/sys/unix/args.rs

@@ -78,19 +78,20 @@ mod imp {
     use crate::marker::PhantomData;
     use crate::os::unix::prelude::*;
     use crate::ptr;
+    use crate::sync::atomic::{AtomicIsize, AtomicPtr, Ordering};
 
     use crate::sys_common::mutex::Mutex;
 
-    static mut ARGC: isize = 0;
-    static mut ARGV: *const *const u8 = ptr::null();
+    static ARGC: AtomicIsize = AtomicIsize::new(0);
+    static ARGV: AtomicPtr<*const u8> = AtomicPtr::new(ptr::null_mut());
     // We never call `ENV_LOCK.init()`, so it is UB to attempt to
     // acquire this mutex reentrantly!
     static LOCK: Mutex = Mutex::new();
 
     unsafe fn really_init(argc: isize, argv: *const *const u8) {
         let _guard = LOCK.lock();
-        ARGC = argc;
-        ARGV = argv;
+        ARGC.store(argc, Ordering::Relaxed);
+        ARGV.store(argv as *mut _, Ordering::Relaxed);
     }
 
     #[inline(always)]
@@ -126,8 +127,8 @@ mod imp {
 
     pub unsafe fn cleanup() {
         let _guard = LOCK.lock();
-        ARGC = 0;
-        ARGV = ptr::null();
+        ARGC.store(0, Ordering::Relaxed);
+        ARGV.store(ptr::null_mut(), Ordering::Relaxed);
     }
 
     pub fn args() -> Args {
@@ -137,9 +138,11 @@ mod imp {
     fn clone() -> Vec<OsString> {
         unsafe {
             let _guard = LOCK.lock();
-            (0..ARGC)
+            let argc = ARGC.load(Ordering::Relaxed);
+            let argv = ARGV.load(Ordering::Relaxed);
+            (0..argc)
                 .map(|i| {
-                    let cstr = CStr::from_ptr(*ARGV.offset(i) as *const libc::c_char);
+                    let cstr = CStr::from_ptr(*argv.offset(i) as *const libc::c_char);
                     OsStringExt::from_vec(cstr.to_bytes().to_vec())
                 })
                 .collect()

src/libstd/sys/unix/stack_overflow.rs

@@ -48,6 +48,7 @@ mod imp {
     use libc::{sigaltstack, SIGSTKSZ, SS_DISABLE};
     use libc::{MAP_ANON, MAP_PRIVATE, PROT_NONE, PROT_READ, PROT_WRITE, SIGSEGV};
 
+    use crate::sync::atomic::{AtomicBool, AtomicPtr, Ordering};
     use crate::sys::unix::os::page_size;
     use crate::sys_common::thread_info;
 
@@ -113,8 +114,8 @@ mod imp {
         }
     }
 
-    static mut MAIN_ALTSTACK: *mut libc::c_void = ptr::null_mut();
-    static mut NEED_ALTSTACK: bool = false;
+    static MAIN_ALTSTACK: AtomicPtr<libc::c_void> = AtomicPtr::new(ptr::null_mut());
+    static NEED_ALTSTACK: AtomicBool = AtomicBool::new(false);
 
     pub unsafe fn init() {
         let mut action: sigaction = mem::zeroed();
@@ -125,17 +126,17 @@ mod imp {
                 action.sa_flags = SA_SIGINFO | SA_ONSTACK;
                 action.sa_sigaction = signal_handler as sighandler_t;
                 sigaction(signal, &action, ptr::null_mut());
-                NEED_ALTSTACK = true;
+                NEED_ALTSTACK.store(true, Ordering::Relaxed);
             }
         }
 
         let handler = make_handler();
-        MAIN_ALTSTACK = handler._data;
+        MAIN_ALTSTACK.store(handler._data, Ordering::Relaxed);
         mem::forget(handler);
     }
 
     pub unsafe fn cleanup() {
-        Handler { _data: MAIN_ALTSTACK };
+        Handler { _data: MAIN_ALTSTACK.load(Ordering::Relaxed) };
     }
 
     unsafe fn get_stackp() -> *mut libc::c_void {
@@ -176,7 +177,7 @@ mod imp {
     }
 
     pub unsafe fn make_handler() -> Handler {
-        if !NEED_ALTSTACK {
+        if !NEED_ALTSTACK.load(Ordering::Relaxed) {
             return Handler::null();
         }
         let mut stack = mem::zeroed();

src/libstd/sys/unix/thread.rs

@@ -246,10 +246,11 @@ pub mod guard {
     use libc::{MAP_ANON, MAP_FAILED, MAP_FIXED, MAP_PRIVATE, PROT_NONE, PROT_READ, PROT_WRITE};
 
     use crate::ops::Range;
+    use crate::sync::atomic::{AtomicUsize, Ordering};
     use crate::sys::os;
 
     // This is initialized in init() and only read from after
-    static mut PAGE_SIZE: usize = 0;
+    static PAGE_SIZE: AtomicUsize = AtomicUsize::new(0);
 
     pub type Guard = Range<usize>;
 
@@ -275,7 +276,7 @@ pub mod guard {
 
         let stackaddr = if libc::pthread_main_np() == 1 {
             // main thread
-            current_stack.ss_sp as usize - current_stack.ss_size + PAGE_SIZE
+            current_stack.ss_sp as usize - current_stack.ss_size + PAGE_SIZE.load(Ordering::Relaxed)
         } else {
             // new thread
             current_stack.ss_sp as usize - current_stack.ss_size
@@ -310,7 +311,8 @@ pub mod guard {
 
     // Precondition: PAGE_SIZE is initialized.
     unsafe fn get_stack_start_aligned() -> Option<*mut libc::c_void> {
-        assert!(PAGE_SIZE != 0);
+        let page_size = PAGE_SIZE.load(Ordering::Relaxed);
+        assert!(page_size != 0);
         let stackaddr = get_stack_start()?;
 
         // Ensure stackaddr is page aligned! A parent process might
@@ -319,16 +321,17 @@ pub mod guard {
         // stackaddr < stackaddr + stacksize, so if stackaddr is not
         // page-aligned, calculate the fix such that stackaddr <
         // new_page_aligned_stackaddr < stackaddr + stacksize
-        let remainder = (stackaddr as usize) % PAGE_SIZE;
+        let remainder = (stackaddr as usize) % page_size;
         Some(if remainder == 0 {
             stackaddr
         } else {
-            ((stackaddr as usize) + PAGE_SIZE - remainder) as *mut libc::c_void
+            ((stackaddr as usize) + page_size - remainder) as *mut libc::c_void
         })
     }
 
     pub unsafe fn init() -> Option<Guard> {
-        PAGE_SIZE = os::page_size();
+        let page_size = os::page_size();
+        PAGE_SIZE.store(page_size, Ordering::Relaxed);
 
         let stackaddr = get_stack_start_aligned()?;
 
@@ -344,7 +347,7 @@ pub mod guard {
             // faulting, so our handler can report "stack overflow", and
             // trust that the kernel's own stack guard will work.
             let stackaddr = stackaddr as usize;
-            Some(stackaddr - PAGE_SIZE..stackaddr)
+            Some(stackaddr - page_size..stackaddr)
         } else {
             // Reallocate the last page of the stack.
             // This ensures SIGBUS will be raised on
@@ -356,7 +359,7 @@ pub mod guard {
             // no permissions at all. See issue #50313.
             let result = mmap(
                 stackaddr,
-                PAGE_SIZE,
+                page_size,
                 PROT_READ | PROT_WRITE,
                 MAP_PRIVATE | MAP_ANON | MAP_FIXED,
                 -1,
@@ -366,22 +369,22 @@ pub mod guard {
                 panic!("failed to allocate a guard page");
             }
 
-            let result = mprotect(stackaddr, PAGE_SIZE, PROT_NONE);
+            let result = mprotect(stackaddr, page_size, PROT_NONE);
             if result != 0 {
                 panic!("failed to protect the guard page");
             }
 
             let guardaddr = stackaddr as usize;
             let offset = if cfg!(target_os = "freebsd") { 2 } else { 1 };
 
-            Some(guardaddr..guardaddr + offset * PAGE_SIZE)
+            Some(guardaddr..guardaddr + offset * page_size)
         }
     }
 
     #[cfg(any(target_os = "macos", target_os = "openbsd", target_os = "solaris"))]
     pub unsafe fn current() -> Option<Guard> {
         let stackaddr = get_stack_start()? as usize;
-        Some(stackaddr - PAGE_SIZE..stackaddr)
+        Some(stackaddr - PAGE_SIZE.load(Ordering::Relaxed)..stackaddr)
     }
 
     #[cfg(any(
@@ -413,7 +416,7 @@ pub mod guard {
             ret = if cfg!(target_os = "freebsd") {
                 // FIXME does freebsd really fault *below* the guard addr?
                 let guardaddr = stackaddr - guardsize;
-                Some(guardaddr - PAGE_SIZE..guardaddr)
+                Some(guardaddr - PAGE_SIZE.load(Ordering::Relaxed)..guardaddr)
             } else if cfg!(target_os = "netbsd") {
                 Some(stackaddr - guardsize..stackaddr)
             } else if cfg!(all(target_os = "linux", target_env = "gnu")) {