From ff13b738570e3299f075bb14efa63ebe8cb265f2 Mon Sep 17 00:00:00 2001
From: Evan Wies <evan@neomantra.net>
Date: Thu, 27 Aug 2026 17:32:32 -0400
Subject: [PATCH] runtime: block signal_recv on targets without signal delivery

The signal_recv stub returns immediately. After signal.Notify starts
the signal goroutine, os/signal.loop calls the stub continuously.
On cooperative schedulers, this prevents other goroutines from
running. On js/wasm, it also prevents control from returning to
the host.

Call deadlock() to block the signal goroutine permanently. These
targets cannot deliver signals.

Add a regression test that calls signal.Notify and then sleeps.
The test checks that the main goroutine can resume and exit.
Skip this test on Windows, which has no signal implementation.

Fixes #5619

Signed-off-by: Evan Wies <evan@neomantra.net>
---
 main_test.go              | 10 +++++++++-
 src/runtime/signalstub.go |  7 ++++++-
 testdata/signalnotify.go  | 14 ++++++++++++++
 testdata/signalnotify.txt |  1 +
 4 files changed, 30 insertions(+), 2 deletions(-)
 create mode 100644 testdata/signalnotify.go
 create mode 100644 testdata/signalnotify.txt

diff --git a/main_test.go b/main_test.go
index ae4d7406a7..a13d42803c 100644
--- a/main_test.go
+++ b/main_test.go
@@ -81,6 +81,7 @@ func TestBuild(t *testing.T) {
 		"print.go",
 		"reflect.go",
 		"signal.go",
+		"signalnotify.go",
 		"slice.go",
 		"sort.go",
 		"stdlib.go",
@@ -440,7 +441,14 @@ func runPlatTests(options compileopts.Options, tests []string, t *testing.T) {
 				continue
 			}
 		}
-		if isWebAssembly || isBaremetal || options.GOOS == "windows" {
+		if options.GOOS == "windows" {
+			switch name {
+			case "signal.go", "signalnotify.go":
+				// os/signal does not link on Windows.
+				continue
+			}
+		}
+		if isWebAssembly || isBaremetal {
 			switch name {
 			case "signal.go":
 				// Signals only work on POSIX-like systems.
diff --git a/src/runtime/signalstub.go b/src/runtime/signalstub.go
index fd7d2606a9..995255c192 100644
--- a/src/runtime/signalstub.go
+++ b/src/runtime/signalstub.go
@@ -18,4 +18,9 @@ func signal_ignore(uint32) {}
 func signal_waitUntilIdle() {}
 
 //go:linkname signal_recv os/signal.signal_recv
-func signal_recv() uint32 { return ^uint32(0) }
+func signal_recv() uint32 {
+	// Block to prevent os/signal.loop from running continuously.
+	// See https://go.dev/src/os/signal/signal_unix.go.
+	deadlock()
+	return 0
+}
diff --git a/testdata/signalnotify.go b/testdata/signalnotify.go
new file mode 100644
index 0000000000..ae8f7a23fe
--- /dev/null
+++ b/testdata/signalnotify.go
@@ -0,0 +1,14 @@
+package main
+
+import (
+	"os"
+	"os/signal"
+	"time"
+)
+
+func main() {
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt)
+	time.Sleep(10 * time.Millisecond)
+	println("done")
+}
diff --git a/testdata/signalnotify.txt b/testdata/signalnotify.txt
new file mode 100644
index 0000000000..19f86f493a
--- /dev/null
+++ b/testdata/signalnotify.txt
@@ -0,0 +1 @@
+done