runtime: crash if a signal is received with bad G and no extra M
When we receive a signal, if G is nil we call badsignal, which
calls needm. When cgo is not used, there is no extra M, so needm
will just hang. In this situation, even GOTRACEBACK=crash cannot
get a stack trace, as we're in the signal handler and cannot
receive another signal (SIGQUIT).
Instead, just crash.
For #35554.
Updates #34391.
Change-Id: I061ac43fc0ac480435c050083096d126b149d21f
Reviewed-on: https://go-review.googlesource.com/c/go/+/206959
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/runtime/signal_unix.go b/src/runtime/signal_unix.go
index 35e6412..f42de36 100644
--- a/src/runtime/signal_unix.go
+++ b/src/runtime/signal_unix.go
@@ -861,11 +861,22 @@
throw("signal received during fork")
}
+var badginsignalMsg = "fatal: bad g in signal handler\n"
+
// This runs on a foreign stack, without an m or a g. No stack split.
//go:nosplit
//go:norace
//go:nowritebarrierrec
func badsignal(sig uintptr, c *sigctxt) {
+ if !iscgo && !cgoHasExtraM {
+ // There is no extra M. needm will not be able to grab
+ // an M. Instead of hanging, just crash.
+ // Cannot call split-stack function as there is no G.
+ s := stringStructOf(&badginsignalMsg)
+ write(2, s.str, int32(s.len))
+ exit(2)
+ *(*uintptr)(unsafe.Pointer(uintptr(123))) = 2
+ }
needm(0)
if !sigsend(uint32(sig)) {
// A foreign thread received the signal sig, and the
