text: // 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 <sys/types.h>
  #include <dlfcn.h>
  #include <errno.h>
  #include <pthread.h>
  #include <signal.h>
  #include <string.h>
  #include "libcgo.h"
  
  static void* threadentry(void*);
  static void (*setg_gcc)(void*);
  
  // TCB_SIZE is sizeof(struct thread_control_block),
  // as defined in /usr/src/lib/librthread/tcb.h
  #define TCB_SIZE (4 * sizeof(void *))
  #define TLS_SIZE (2 * sizeof(void *))
  
  void *__get_tcb(void);
  void __set_tcb(void *);
  
  static int (*sys_pthread_create)(pthread_t *thread, const pthread_attr_t *attr,
  	void *(*start_routine)(void *), void *arg);
  
  struct thread_args {
  	void *(*func)(void *);
  	void *arg;
  };
  
  static void
  tcb_fixup(int mainthread)
  {
  	void *newtcb, *oldtcb;
  
  	// The OpenBSD ld.so(1) does not currently support PT_TLS. As a result,
  	// we need to allocate our own TLS space while preserving the existing
  	// TCB that has been setup via librthread.
  
  	newtcb = malloc(TCB_SIZE + TLS_SIZE);
  	if(newtcb == NULL)
  		abort();
  
  	// The signal trampoline expects the TLS slots to be zeroed.
  	bzero(newtcb, TLS_SIZE);
  
  	oldtcb = __get_tcb();
  	bcopy(oldtcb, newtcb + TLS_SIZE, TCB_SIZE);
  	__set_tcb(newtcb + TLS_SIZE);
  
  	// NOTE(jsing, minux): we can't free oldtcb without causing double-free
  	// problem. so newtcb will be memory leaks. Get rid of this when OpenBSD
  	// has proper support for PT_TLS.
  }
  
  static void *
  thread_start_wrapper(void *arg)
  {
  	struct thread_args args = *(struct thread_args *)arg;
  
  	free(arg);
  	tcb_fixup(0);
  
  	return args.func(args.arg);
  }
  
  int
  pthread_create(pthread_t *thread, const pthread_attr_t *attr,
  	void *(*start_routine)(void *), void *arg)
  {
  	struct thread_args *p;
  
  	p = malloc(sizeof(*p));
  	if(p == NULL) {
  		errno = ENOMEM;
  		return -1;
  	}
  	p->func = start_routine;
  	p->arg = arg;
  
  	return sys_pthread_create(thread, attr, thread_start_wrapper, p);
  }
  
  void
  x_cgo_init(G *g, void (*setg)(void*))
  {
  	pthread_attr_t attr;
  	size_t size;
  	void *handle;
  
  	setg_gcc = setg;
  	pthread_attr_init(&attr);
  	pthread_attr_getstacksize(&attr, &size);
  	g->stacklo = (uintptr)&attr - size + 4096;
  	pthread_attr_destroy(&attr);
  
  	// Locate symbol for the system pthread_create function.
  	handle = dlopen("libpthread.so", RTLD_LAZY);
  	if(handle == NULL) {
  		fprintf(stderr, "dlopen: failed to load libpthread: %s\n", dlerror());
  		abort();
  	}
  	sys_pthread_create = dlsym(handle, "pthread_create");
  	if(sys_pthread_create == NULL) {
  		fprintf(stderr, "dlsym: failed to find pthread_create: %s\n", dlerror());
  		abort();
  	}
  	dlclose(handle);
  
  	tcb_fixup(1);
  }
  
  
  void
  _cgo_sys_thread_start(ThreadStart *ts)
  {
  	pthread_attr_t attr;
  	sigset_t ign, oset;
  	pthread_t p;
  	size_t size;
  	int err;
  
  	sigfillset(&ign);
  	pthread_sigmask(SIG_SETMASK, &ign, &oset);
  
  	pthread_attr_init(&attr);
  	pthread_attr_getstacksize(&attr, &size);
  
  	// Leave stacklo=0 and set stackhi=size; mstack will do the rest.
  	ts->g->stackhi = size;
  	err = sys_pthread_create(&p, &attr, threadentry, ts);
  
  	pthread_sigmask(SIG_SETMASK, &oset, nil);
  
  	if (err != 0) {
  		fprintf(stderr, "runtime/cgo: pthread_create failed: %s\n", strerror(err));
  		abort();
  	}
  }
  
  static void*
  threadentry(void *v)
  {
  	ThreadStart ts;
  
  	tcb_fixup(0);
  
  	ts = *(ThreadStart*)v;
  	free(v);
  
  	/*
  	 * Set specific keys.
  	 */
  	setg_gcc((void*)ts.g);
  
  	crosscall_amd64(ts.fn);
  	return nil;
  }
  