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