1 files changed, 69 insertions, 0 deletions
diff --git a/src/runtime/cgo/gcc_util.c b/src/runtime/cgo/gcc_util.c
new file mode 100644
index 0000000..3fcb48c
--- /dev/null
+++ b/src/runtime/cgo/gcc_util.c
@@ -0,0 +1,69 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "libcgo.h"
+
+/* Stub for creating a new thread */
+void
+x_cgo_thread_start(ThreadStart *arg)
+{
+	ThreadStart *ts;
+
+	/* Make our own copy that can persist after we return. */
+	_cgo_tsan_acquire();
+	ts = malloc(sizeof *ts);
+	_cgo_tsan_release();
+	if(ts == nil) {
+		fprintf(stderr, "runtime/cgo: out of memory in thread_start\n");
+		abort();
+	}
+	*ts = *arg;
+
+	_cgo_sys_thread_start(ts);	/* OS-dependent half */
+}
+
+#ifndef CGO_TSAN
+void(* const _cgo_yield)() = NULL;
+#else
+
+#include <string.h>
+
+char x_cgo_yield_strncpy_src = 0;
+char x_cgo_yield_strncpy_dst = 0;
+size_t x_cgo_yield_strncpy_n = 0;
+
+/*
+Stub for allowing libc interceptors to execute.
+
+_cgo_yield is set to NULL if we do not expect libc interceptors to exist.
+*/
+static void
+x_cgo_yield()
+{
+	/*
+	The libc function(s) we call here must form a no-op and include at least one
+	call that triggers TSAN to process pending asynchronous signals.
+
+	sleep(0) would be fine, but it's not portable C (so it would need more header
+	guards).
+	free(NULL) has a fast-path special case in TSAN, so it doesn't
+	trigger signal delivery.
+	free(malloc(0)) would work (triggering the interceptors in malloc), but
+	it also runs a bunch of user-supplied malloc hooks.
+
+	So we choose strncpy(_, _, 0): it requires an extra header,
+	but it's standard and should be very efficient.
+
+	GCC 7 has an unfortunate habit of optimizing out strncpy calls (see
+	https://golang.org/issue/21196), so the arguments here need to be global
+	variables with external linkage in order to ensure that the call traps all the
+	way down into libc.
+	*/
+	strncpy(&x_cgo_yield_strncpy_dst, &x_cgo_yield_strncpy_src,
+	        x_cgo_yield_strncpy_n);
+}
+
+void(* const _cgo_yield)() = &x_cgo_yield;
+
+#endif  /* GO_TSAN */