save and restore errno

Author: hanna-kruppe

.github/workflows/test.yaml

@@ -119,6 +119,7 @@ jobs:
           cd signal-hook-registry
           sed -i -e '/signal-hook =/d' Cargo.toml
           sed -i -e 's/libc = "^0.2"/libc = "=0.2.156"/' Cargo.toml
+          sed -i -e 's/errno = ">=0.2, <0.4"/errno = "0.2"/' Cargo.toml
           cargo check
 
   ancient:
@@ -144,6 +145,7 @@ jobs:
         run: |
           rm Cargo.lock
           sed -i -e 's/libc = "^0.2"/libc = "=0.2.156"/' Cargo.toml
+          sed -i -e 's/errno = ">=0.2, <0.4"/errno = "0.2"/' signal-hook-registry/Cargo.toml
           cargo update
           cargo check --no-default-features
 

Cargo.lock

@@ -12,6 +12,7 @@ rm -f Cargo.lock
 if [ "$RUST_VERSION" = 1.36.0 ] || [ "$RUST_VERSION" = 1.40.0 ] ; then
 	sed -i -e 's/libc = "^0.2"/libc = "=0.2.156"/' Cargo.toml
 	sed -i -e 's/cc = { version = "^1"/cc = { version = "=1.0.79"/' Cargo.toml
+	sed -i -e 's/errno = ">=0.2, <0.4"/errno = "0.2"/' signal-hook-registry/Cargo.toml
 fi
 
 cargo build --all --exclude signal-hook-async-std --exclude signal-hook-tokio

ci-check.sh

@@ -20,6 +20,7 @@ maintenance = { status = "actively-developed" }
 
 [dependencies]
 libc = "^0.2"
+errno = ">=0.2, <0.4"
 
 [dev-dependencies]
 signal-hook = { version = "~0.3", path = ".." }

signal-hook-registry/Cargo.toml

@@ -62,6 +62,7 @@
 //! [signal-hook]: https://docs.rs/signal-hook
 //! [async-signal-safe]: http://www.man7.org/linux/man-pages/man7/signal-safety.7.html
 
+extern crate errno;
 extern crate libc;
 
 mod half_lock;
@@ -78,6 +79,7 @@ use std::sync::atomic::{AtomicPtr, Ordering};
 use std::sync::ONCE_INIT;
 use std::sync::{Arc, Once};
 
+use errno::Errno;
 #[cfg(not(windows))]
 use libc::{c_int, c_void, sigaction, siginfo_t};
 #[cfg(windows)]
@@ -338,6 +340,8 @@ impl GlobalData {
 
 #[cfg(windows)]
 extern "C" fn handler(sig: c_int) {
+    let _errno = ErrnoGuard::new();
+
     if sig != SIGFPE {
         // Windows CRT `signal` resets handler every time, unless for SIGFPE.
         // Reregister the handler to retain maximal compatibility.
@@ -385,6 +389,8 @@ extern "C" fn handler(sig: c_int) {
 // cfg_attr is needed because the `allow(clippy::lint)` syntax was added in Rust 1.31
 #[cfg_attr(clippy, allow(clippy::incompatible_msrv))]
 extern "C" fn handler(sig: c_int, info: *mut siginfo_t, data: *mut c_void) {
+    let _errno = ErrnoGuard::new();
+
     let globals = GlobalData::get();
     let fallback = globals.race_fallback.read();
     let sigdata = globals.data.read();
@@ -422,6 +428,20 @@ extern "C" fn handler(sig: c_int, info: *mut siginfo_t, data: *mut c_void) {
     }
 }
 
+struct ErrnoGuard(Errno);
+
+impl ErrnoGuard {
+    fn new() -> Self {
+        ErrnoGuard(errno::errno())
+    }
+}
+
+impl Drop for ErrnoGuard {
+    fn drop(&mut self) {
+        errno::set_errno(self.0);
+    }
+}
+
 /// List of forbidden signals.
 ///
 /// Some signals are impossible to replace according to POSIX and some are so special that this
@@ -834,4 +854,20 @@ mod tests {
         // The next time unregistering does nothing and tells us so.
         assert!(!unregister(signal));
     }
+
+    /// Check that errno is not clobbered by the signal handler.
+    #[test]
+    fn save_restore_errno() {
+        const MAGIC_ERRNO: i32 = 123456;
+        let action = move || {
+            errno::set_errno(Errno(MAGIC_ERRNO));
+        };
+        unsafe {
+            register(SIGUSR1, action).unwrap();
+            libc::raise(SIGUSR1);
+        }
+        // NB: raise() might clobber errno on some platforms, so this test isn't waterproof. But it
+        // fails at least sometimes on some platforms if the errno save/restore is removed.
+        assert!(errno::errno().0 != MAGIC_ERRNO);
+    }
 }