1 // Copyright 2015 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 //go:build unix
6
7 // When cross-compiling with clang to linux/armv5, atomics are emulated
8 // and cause a compiler warning. This results in a build failure since
9 // cgo uses -Werror. See #65290.
10 #pragma GCC diagnostic ignored "-Wpragmas"
11 #pragma GCC diagnostic ignored "-Wunknown-warning-option"
12 #pragma GCC diagnostic ignored "-Watomic-alignment"
13
14 #include <pthread.h>
15 #include <errno.h>
16 #include <stdio.h>
17 #include <stdlib.h>
18 #include <string.h> // strerror
19 #include <time.h>
20 #include "libcgo.h"
21 #include "libcgo_unix.h"
22
23 static pthread_cond_t runtime_init_cond = PTHREAD_COND_INITIALIZER;
24 static pthread_mutex_t runtime_init_mu = PTHREAD_MUTEX_INITIALIZER;
25 static int runtime_init_done;
26
27 // pthread_g is a pthread specific key, for storing the g that binded to the C thread.
28 // The registered pthread_key_destructor will dropm, when the pthread-specified value g is not NULL,
29 // while a C thread is exiting.
30 static pthread_key_t pthread_g;
31 static void pthread_key_destructor(void* g);
32 uintptr_t x_cgo_pthread_key_created;
33 void (*x_crosscall2_ptr)(void (*fn)(void *), void *, int, size_t);
34
35 // The context function, used when tracing back C calls into Go.
36 static void (*cgo_context_function)(struct context_arg*);
37
38 void
39 x_cgo_sys_thread_create(void* (*func)(void*), void* arg) {
40 pthread_attr_t attr;
41 pthread_t p;
42 int err;
43
44 pthread_attr_init(&attr);
45 pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
46 err = _cgo_try_pthread_create(&p, &attr, func, arg);
47 if (err != 0) {
48 fprintf(stderr, "pthread_create failed: %s", strerror(err));
49 abort();
50 }
51 }
52
53 uintptr_t
54 _cgo_wait_runtime_init_done(void) {
55 void (*pfn)(struct context_arg*);
56 int done;
57
58 pfn = __atomic_load_n(&cgo_context_function, __ATOMIC_CONSUME);
59
60 done = 2;
61 if (__atomic_load_n(&runtime_init_done, __ATOMIC_CONSUME) != done) {
62 pthread_mutex_lock(&runtime_init_mu);
63 while (__atomic_load_n(&runtime_init_done, __ATOMIC_CONSUME) == 0) {
64 pthread_cond_wait(&runtime_init_cond, &runtime_init_mu);
65 }
66
67 // The key and x_cgo_pthread_key_created are for the whole program,
68 // whereas the specific and destructor is per thread.
69 if (x_cgo_pthread_key_created == 0 && pthread_key_create(&pthread_g, pthread_key_destructor) == 0) {
70 x_cgo_pthread_key_created = 1;
71 }
72
73
74 // TODO(iant): For the case of a new C thread calling into Go, such
75 // as when using -buildmode=c-archive, we know that Go runtime
76 // initialization is complete but we do not know that all Go init
77 // functions have been run. We should not fetch cgo_context_function
78 // until they have been, because that is where a call to
79 // SetCgoTraceback is likely to occur. We are going to wait for Go
80 // initialization to be complete anyhow, later, by waiting for
81 // main_init_done to be closed in cgocallbackg1. We should wait here
82 // instead. See also issue #15943.
83 pfn = __atomic_load_n(&cgo_context_function, __ATOMIC_CONSUME);
84
85 __atomic_store_n(&runtime_init_done, done, __ATOMIC_RELEASE);
86 pthread_mutex_unlock(&runtime_init_mu);
87 }
88
89 if (pfn != nil) {
90 struct context_arg arg;
91
92 arg.Context = 0;
93 (*pfn)(&arg);
94 return arg.Context;
95 }
96 return 0;
97 }
98
99 // _cgo_set_stacklo sets g->stacklo based on the stack size.
100 // This is common code called from x_cgo_init, which is itself
101 // called by rt0_go in the runtime package.
102 void _cgo_set_stacklo(G *g, uintptr *pbounds)
103 {
104 uintptr bounds[2];
105
106 // pbounds can be passed in by the caller; see gcc_linux_amd64.c.
107 if (pbounds == NULL) {
108 pbounds = &bounds[0];
109 }
110
111 x_cgo_getstackbound(pbounds);
112
113 g->stacklo = *pbounds;
114
115 // Sanity check the results now, rather than getting a
116 // morestack on g0 crash.
117 if (g->stacklo >= g->stackhi) {
118 fprintf(stderr, "runtime/cgo: bad stack bounds: lo=%p hi=%p\n", (void*)(g->stacklo), (void*)(g->stackhi));
119 abort();
120 }
121 }
122
123 // Store the g into a thread-specific value associated with the pthread key pthread_g.
124 // And pthread_key_destructor will dropm when the thread is exiting.
125 void x_cgo_bindm(void* g) {
126 // We assume this will always succeed, otherwise, there might be extra M leaking,
127 // when a C thread exits after a cgo call.
128 // We only invoke this function once per thread in runtime.needAndBindM,
129 // and the next calls just reuse the bound m.
130 pthread_setspecific(pthread_g, g);
131 }
132
133 void
134 x_cgo_notify_runtime_init_done(void* dummy __attribute__ ((unused))) {
135 pthread_mutex_lock(&runtime_init_mu);
136 __atomic_store_n(&runtime_init_done, 1, __ATOMIC_RELEASE);
137 pthread_cond_broadcast(&runtime_init_cond);
138 pthread_mutex_unlock(&runtime_init_mu);
139 }
140
141 // Sets the context function to call to record the traceback context
142 // when calling a Go function from C code. Called from runtime.SetCgoTraceback.
143 void x_cgo_set_context_function(void (*context)(struct context_arg*)) {
144 __atomic_store_n(&cgo_context_function, context, __ATOMIC_RELEASE);
145 }
146
147 // Gets the context function.
148 void (*(_cgo_get_context_function(void)))(struct context_arg*) {
149 return __atomic_load_n(&cgo_context_function, __ATOMIC_CONSUME);
150 }
151
152 // _cgo_try_pthread_create retries pthread_create if it fails with
153 // EAGAIN.
154 int
155 _cgo_try_pthread_create(pthread_t* thread, const pthread_attr_t* attr, void* (*pfn)(void*), void* arg) {
156 int tries;
157 int err;
158 struct timespec ts;
159
160 for (tries = 0; tries < 20; tries++) {
161 err = pthread_create(thread, attr, pfn, arg);
162 if (err == 0) {
163 return 0;
164 }
165 if (err != EAGAIN) {
166 return err;
167 }
168 ts.tv_sec = 0;
169 ts.tv_nsec = (tries + 1) * 1000 * 1000; // Milliseconds.
170 nanosleep(&ts, nil);
171 }
172 return EAGAIN;
173 }
174
175 static void
176 pthread_key_destructor(void* g) {
177 if (x_crosscall2_ptr != NULL) {
178 // fn == NULL means dropm.
179 // We restore g by using the stored g, before dropm in runtime.cgocallback,
180 // since the g stored in the TLS by Go might be cleared in some platforms,
181 // before this destructor invoked.
182 x_crosscall2_ptr(NULL, g, 0, 0);
183 }
184 }
185
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