1 // Copyright 2009 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 #include "libcgo.h" 6 7 /* Stub for creating a new thread */ 8 void 9 x_cgo_thread_start(ThreadStart *arg) 10 { 11 ThreadStart *ts; 12 13 /* Make our own copy that can persist after we return. */ 14 _cgo_tsan_acquire(); 15 ts = malloc(sizeof *ts); 16 _cgo_tsan_release(); 17 if(ts == nil) { 18 fprintf(stderr, "runtime/cgo: out of memory in thread_start\n"); 19 abort(); 20 } 21 *ts = *arg; 22 23 _cgo_sys_thread_start(ts); /* OS-dependent half */ 24 } 25 26 #ifndef CGO_TSAN 27 void(* const _cgo_yield)() = NULL; 28 #else 29 30 #include <string.h> 31 32 char x_cgo_yield_strncpy_src = 0; 33 char x_cgo_yield_strncpy_dst = 0; 34 size_t x_cgo_yield_strncpy_n = 0; 35 36 /* 37 Stub for allowing libc interceptors to execute. 38 39 _cgo_yield is set to NULL if we do not expect libc interceptors to exist. 40 */ 41 static void 42 x_cgo_yield() 43 { 44 /* 45 The libc function(s) we call here must form a no-op and include at least one 46 call that triggers TSAN to process pending asynchronous signals. 47 48 sleep(0) would be fine, but it's not portable C (so it would need more header 49 guards). 50 free(NULL) has a fast-path special case in TSAN, so it doesn't 51 trigger signal delivery. 52 free(malloc(0)) would work (triggering the interceptors in malloc), but 53 it also runs a bunch of user-supplied malloc hooks. 54 55 So we choose strncpy(_, _, 0): it requires an extra header, 56 but it's standard and should be very efficient. 57 58 GCC 7 has an unfortunate habit of optimizing out strncpy calls (see 59 https://golang.org/issue/21196), so the arguments here need to be global 60 variables with external linkage in order to ensure that the call traps all the 61 way down into libc. 62 */ 63 strncpy(&x_cgo_yield_strncpy_dst, &x_cgo_yield_strncpy_src, 64 x_cgo_yield_strncpy_n); 65 } 66 67 void(* const _cgo_yield)() = &x_cgo_yield; 68 69 #endif /* GO_TSAN */ 70
