runtime: M-targeted signals for Linux

We'll add a test once all of the POSIX platforms are done.

For #10958, #24543.

Change-Id: If7e3f14e8391791364877629bf415d9f8e788b0a
Reviewed-on: https://go-review.googlesource.com/c/go/+/201401
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/src/runtime/os_linux.go b/src/runtime/os_linux.go
index b1ddf53dd1..20b947f250 100644
--- a/src/runtime/os_linux.go
+++ b/src/runtime/os_linux.go
@@ -332,7 +332,9 @@ func gettid() uint32
 func minit() {
 	minitSignals()
 
-	// for debuggers, in case cgo created the thread
+	// Cgo-created threads and the bootstrap m are missing a
+	// procid. We need this for asynchronous preemption and its
+	// useful in debuggers.
 	getg().m.procid = uint64(gettid())
 }
 
@@ -454,3 +456,11 @@ func sysSigaction(sig uint32, new, old *sigactiont) {
 // rt_sigaction is implemented in assembly.
 //go:noescape
 func rt_sigaction(sig uintptr, new, old *sigactiont, size uintptr) int32
+
+func getpid() int
+func tgkill(tgid, tid, sig int)
+
+// signalM sends a signal to mp.
+func signalM(mp *m, sig int) {
+	tgkill(getpid(), int(mp.procid), sig)
+}