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// 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 */
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