fix: signal.SIGINT and signal() raise NotImplementedError on wasi (#8986)

* fix: signal.SIGINT and signal() raise NotImplementedError on wasi

- Problem: signal.SIGINT and friends don't exist on wasi, and signal.signal()
  is hard-stubbed to raise NotImplementedError there
- Cause: wasi-libc emulates signal()/raise() in a separate opt-in library
  that Rust's own wasm32-wasip1 target distribution doesn't ship
- Fix: vendor wasi-sdk's prebuilt libwasi-emulated-signal.a, link it for
  wasm32-wasip1, and wire SIGINT/SIGABRT/SIGFPE/SIGILL/SIGSEGV/SIGTERM,
  signal()/getsignal()/raise_signal() through it. CPython's own WASI build
  links the same library

Assisted-by: Claude Code:claude-sonnet-5
Signed-off-by: Jiwoo Ahn <ikwydls1314@gmail.com>

* Group WASI signal definitions in mod wasm

Move WASI-only types, constants, FFI, and handlers into
`mod wasm` and re-export them with `#[cfg(target_os = "wasi")]`.

Assisted-by: Grok 4.6

---------

Signed-off-by: Jiwoo Ahn <ikwydls1314@gmail.com>
Co-authored-by: Jeong YunWon <jeong@youknowone.org>

.cargo/config.toml

@@ -10,9 +10,12 @@ rustflags = ["--cfg=getrandom_backend=\"wasm_js\""]
 # Enforce a 1 MB stack limit for WASI targets.
 # (Runaway heap growth is fixed by the smaller DataStack chunk
 # and the size‑optimized wasm‑release profile.)
+
 [target.wasm32-wasip1]
 rustflags = [
     "-C", "link-arg=-zstack-size=1048576",
+    "-L", "crates/host_env/vendor/wasm32-wasip1",
+    "-l", "wasi-emulated-signal",
 ]
 
 [target.wasm32-wasip2]

crates/host_env/src/lib.rs

@@ -74,7 +74,7 @@ pub mod pwd;
 pub mod resource;
 #[cfg(all(unix, not(target_os = "redox"), not(target_os = "android")))]
 pub mod shm;
-#[cfg(any(unix, windows))]
+#[cfg(any(unix, windows, target_os = "wasi"))]
 pub mod signal;
 pub mod time;
 

crates/host_env/src/signal.rs

@@ -1,3 +1,4 @@
+#[cfg(any(unix, windows))]
 use std::io;
 #[cfg(windows)]
 use std::sync::Once;
@@ -13,13 +14,83 @@ pub use libc::sighandler_t;
 #[cfg(unix)]
 pub use libc::{SIG_DFL, SIG_ERR, SIG_IGN};
 
-#[cfg(not(unix))]
+#[cfg(not(any(unix, target_os = "wasi")))]
 pub const SIG_DFL: libc::sighandler_t = 0;
-#[cfg(not(unix))]
+#[cfg(not(any(unix, target_os = "wasi")))]
 pub const SIG_IGN: libc::sighandler_t = 1;
-#[cfg(not(unix))]
+#[cfg(not(any(unix, target_os = "wasi")))]
 pub const SIG_ERR: libc::sighandler_t = -1 as _;
 
+/// wasi-libc's userspace emulation of `signal()`/`raise()`, linked from
+/// `libwasi-emulated-signal` (see `crates/host_env/vendor/wasm32-wasip1`).
+/// WebAssembly has no asynchronous signal delivery, so this is a
+/// synchronous, in-process handler table: a handler only runs when this
+/// process's own code calls `raise()`, never from an outside interrupt.
+/// Numbering matches wasi-libc's `bits/signal.h`, the same values CPython's
+/// WASI build gets by linking the same library.
+#[cfg(target_os = "wasi")]
+mod wasm {
+    use std::io;
+
+    #[allow(non_camel_case_types)]
+    pub type sighandler_t = usize;
+
+    pub const SIG_DFL: sighandler_t = 0;
+    pub const SIG_IGN: sighandler_t = 1;
+    pub const SIG_ERR: sighandler_t = -1isize as usize;
+
+    pub const SIGINT: i32 = 2;
+    pub const SIGILL: i32 = 4;
+    pub const SIGABRT: i32 = 6;
+    pub const SIGFPE: i32 = 8;
+    pub const SIGSEGV: i32 = 11;
+    pub const SIGTERM: i32 = 15;
+
+    unsafe extern "C" {
+        fn signal(signum: i32, handler: sighandler_t) -> sighandler_t;
+        fn raise(signum: i32) -> i32;
+    }
+
+    /// # Safety
+    ///
+    /// The caller must ensure `signalnum` is a valid platform signal number.
+    pub unsafe fn probe_handler(signalnum: i32) -> Option<sighandler_t> {
+        let handler = unsafe { signal(signalnum, SIG_IGN) };
+        if handler == SIG_ERR {
+            None
+        } else {
+            unsafe { signal(signalnum, handler) };
+            Some(handler)
+        }
+    }
+
+    /// # Safety
+    ///
+    /// The caller must ensure `signalnum` is a valid platform signal number and
+    /// `handler` is accepted by the platform signal ABI.
+    pub unsafe fn install_handler(
+        signalnum: i32,
+        handler: sighandler_t,
+    ) -> io::Result<sighandler_t> {
+        let old = unsafe { signal(signalnum, handler) };
+        if old == SIG_ERR {
+            return Err(io::Error::last_os_error());
+        }
+        Ok(old)
+    }
+
+    pub fn raise_signal(signalnum: i32) -> io::Result<()> {
+        if unsafe { raise(signalnum) } == 0 {
+            Ok(())
+        } else {
+            Err(io::Error::last_os_error())
+        }
+    }
+}
+
+#[cfg(target_os = "wasi")]
+pub use wasm::*;
+
 #[cfg(unix)]
 pub use libc::{SIG_BLOCK, SIG_SETMASK, SIG_UNBLOCK};
 
@@ -320,7 +391,7 @@ pub fn notify_signal(
     }
 }
 
-#[cfg(unix)]
+#[cfg(any(unix, target_os = "wasi"))]
 pub fn notify_signal(signum: i32, wakeup_fd: i32) {
     if wakeup_fd == -1 {
         return;

crates/host_env/vendor/wasm32-wasip1/README.md

@@ -0,0 +1,16 @@
+# Vendored wasi-libc emulation library
+
+`libwasi-emulated-signal.a` is a prebuilt static library from
+[wasi-sdk](https://github.com/WebAssembly/wasi-sdk), providing wasi-libc's
+userspace emulation of `signal()`/`raise()` for `wasm32-wasip1` (WebAssembly
+has no asynchronous signal delivery, so this is a synchronous, in-process
+handler table, not a real OS signal mechanism).
+
+CPython's own WASI build links the same library
+(`configure.ac`'s `_WASI_EMULATED_SIGNAL` case).
+
+- Source: https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-34/wasi-sysroot-34.0.tar.gz
+  (path: `lib/wasm32-wasip1/libwasi-emulated-signal.a`)
+- License: Apache-2.0 WITH LLVM-exception (same as wasi-libc)
+- sha256: see below
+becc35b856608fb9282d94c70166796e4d7b21e4e1057e625725306e765eb035  crates/host_env/vendor/wasm32-wasip1/libwasi-emulated-signal.a

crates/vm/src/signal.rs

@@ -233,6 +233,10 @@ impl SignalNum {
     #[allow(dead_code, reason = "Not used on all platforms")]
     pub(crate) const SIGINT: Self = Self(libc::SIGINT);
 
+    #[cfg(all(target_os = "wasi", feature = "host_env"))]
+    #[allow(dead_code, reason = "Not used on all platforms")]
+    pub(crate) const SIGINT: Self = Self(rustpython_host_env::signal::SIGINT);
+
     /// Construct [`Self`] without any validation on the signalnum value.
     ///
     /// # Safety

crates/vm/src/stdlib/_signal.rs

@@ -13,7 +13,7 @@ pub(crate) mod _signal {
     use core::sync::atomic::{self, Ordering};
 
     cfg_select! {
-        any(unix, windows) => {
+        any(unix, windows, target_os = "wasi") => {
             use crate::convert::{IntoPyException, TryFromBorrowedObject};
             use rustpython_host_env::signal as host_signal;
         }
@@ -73,11 +73,11 @@ pub(crate) mod _signal {
         }
     }
 
-    #[cfg(any(unix, windows))]
+    #[cfg(any(unix, windows, target_os = "wasi"))]
     #[allow(unused_imports)]
     pub use host_signal::SIG_ERR;
 
-    #[cfg(any(unix, windows))]
+    #[cfg(any(unix, windows, target_os = "wasi"))]
     #[pyattr]
     pub use host_signal::{SIG_DFL, SIG_IGN};
 
@@ -86,22 +86,22 @@ pub(crate) mod _signal {
     #[pyattr]
     use host_signal::{SIG_BLOCK, SIG_SETMASK, SIG_UNBLOCK};
 
-    #[cfg(not(any(unix, windows)))]
+    #[cfg(not(any(unix, windows, target_os = "wasi")))]
     #[pyattr]
     pub const SIG_DFL: sighandler_t = 0;
 
-    #[cfg(not(any(unix, windows)))]
+    #[cfg(not(any(unix, windows, target_os = "wasi")))]
     #[pyattr]
     pub const SIG_IGN: sighandler_t = 1;
 
-    #[cfg(not(any(unix, windows)))]
+    #[cfg(not(any(unix, windows, target_os = "wasi")))]
     #[allow(dead_code)]
     pub const SIG_ERR: sighandler_t = -1 as _;
 
     #[pyattr]
     use crate::signal::NSIG;
 
-    #[cfg(any(unix, windows))]
+    #[cfg(any(unix, windows, target_os = "wasi"))]
     #[pyattr]
     pub use host_signal::{SIGABRT, SIGFPE, SIGILL, SIGINT, SIGSEGV, SIGTERM};
 
@@ -160,7 +160,7 @@ pub(crate) mod _signal {
     const _: () = assert!(SignalNum::VALID_RANGE.start.is_positive());
     const _: () = assert!(SignalNum::VALID_RANGE.end.is_positive());
 
-    #[cfg(any(unix, windows))]
+    #[cfg(any(unix, windows, target_os = "wasi"))]
     pub(super) fn init_signal_handlers(
         module: &Py<crate::builtins::PyModule>,
         vm: &VirtualMachine,
@@ -199,7 +199,7 @@ pub(crate) mod _signal {
         }
     }
 
-    #[cfg(not(any(unix, windows)))]
+    #[cfg(not(any(unix, windows, target_os = "wasi")))]
     #[pyfunction]
     pub fn signal(
         _signalnum: i32,
@@ -209,7 +209,7 @@ pub(crate) mod _signal {
         Err(vm.new_not_implemented_error("signal is not implemented on this platform"))
     }
 
-    #[cfg(any(unix, windows))]
+    #[cfg(any(unix, windows, target_os = "wasi"))]
     #[pyfunction]
     pub fn signal(
         signalnum: SignalNum,
@@ -401,7 +401,7 @@ pub(crate) mod _signal {
         host_signal::siginterrupt(signalnum.into(), flag).map_err(|_| vm.new_last_errno_error())
     }
 
-    #[cfg(any(unix, windows))]
+    #[cfg(any(unix, windows, target_os = "wasi"))]
     #[pyfunction]
     fn raise_signal(signalnum: i32, vm: &VirtualMachine) -> PyResult<()> {
         let signalnum = SignalNum::try_from(signalnum).map_err(cfg_select! {
@@ -506,7 +506,7 @@ pub(crate) mod _signal {
         sigset_to_pyset(old_mask, vm)
     }
 
-    #[cfg(any(unix, windows))]
+    #[cfg(any(unix, windows, target_os = "wasi"))]
     pub extern "C" fn run_signal(signum: i32) {
         signal::TRIGGERS[signum as usize].store(true, Ordering::Relaxed);
         signal::set_triggered();
@@ -535,7 +535,7 @@ pub(crate) mod _signal {
     ) -> PyResult<()> {
         __module_exec(vm, module);
 
-        #[cfg(any(unix, windows))]
+        #[cfg(any(unix, windows, target_os = "wasi"))]
         init_signal_handlers(module, vm);
 
         Ok(())

extra_tests/snippets/stdlib_signal.py

@@ -21,8 +21,8 @@ assert old_signal is signal.SIG_IGN
 assert signal.getsignal(signal.SIGILL) is signal.SIG_DFL
 
 
-# unix
-if "win" not in sys.platform:
+# unix, and not WASI
+if "win" not in sys.platform and sys.platform != "wasi":
     signal.signal(signal.SIGALRM, handler)
     assert signal.getsignal(signal.SIGALRM) is handler