runtime: use a pipe to wake up signal_recv on Darwin

The implementation of semaphores, and therefore notes, used on Darwin
is not async-signal-safe. The runtime has one case where a note needs
to be woken up from a signal handler: the call to notewakeup in sigsend.
That notewakeup call is only called on a single note, and it doesn't
need the full functionality of notes: nothing ever does a timed wait on it.
So change that one note to use a different implementation on Darwin,
based on a pipe. This lets the wakeup code use the write call, which is
async-signal-safe.

Fixes #31264

Change-Id: If705072d7a961dd908ea9d639c8d12b222c64806
Reviewed-on: https://go-review.googlesource.com/c/go/+/184169
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/runtime/sys_darwin.go b/src/runtime/sys_darwin.go
index b50d441d92..376f76dbc5 100644
--- a/src/runtime/sys_darwin.go
+++ b/src/runtime/sys_darwin.go
@@ -197,6 +197,13 @@ func read(fd int32, p unsafe.Pointer, n int32) int32 {
 }
 func read_trampoline()
 
+func pipe() (r, w int32, errno int32) {
+	var p [2]int32
+	errno = libcCall(unsafe.Pointer(funcPC(pipe_trampoline)), noescape(unsafe.Pointer(&p)))
+	return p[0], p[1], errno
+}
+func pipe_trampoline()
+
 //go:nosplit
 //go:cgo_unsafe_args
 func closefd(fd int32) int32 {
@@ -395,6 +402,12 @@ func closeonexec(fd int32) {
 	fcntl(fd, _F_SETFD, _FD_CLOEXEC)
 }
 
+//go:nosplit
+func setNonblock(fd int32) {
+	flags := fcntl(fd, _F_GETFL, 0)
+	fcntl(fd, _F_SETFL, flags|_O_NONBLOCK)
+}
+
 // Tell the linker that the libc_* functions are to be found
 // in a system library, with the libc_ prefix missing.
 
@@ -409,6 +422,7 @@ func closeonexec(fd int32) {
 //go:cgo_import_dynamic libc_close close "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_read read "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_write write "/usr/lib/libSystem.B.dylib"
+//go:cgo_import_dynamic libc_pipe pipe "/usr/lib/libSystem.B.dylib"
 
 //go:cgo_import_dynamic libc_mmap mmap "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_munmap munmap "/usr/lib/libSystem.B.dylib"