github.com/eun/go@v0.0.0-20170811110501-92cfd07a6cfd/src/runtime/os3_solaris.go (about)

     1  // Copyright 2011 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  package runtime
     6  
     7  import "unsafe"
     8  
     9  //go:cgo_export_dynamic runtime.end _end
    10  //go:cgo_export_dynamic runtime.etext _etext
    11  //go:cgo_export_dynamic runtime.edata _edata
    12  
    13  //go:cgo_import_dynamic libc____errno ___errno "libc.so"
    14  //go:cgo_import_dynamic libc_clock_gettime clock_gettime "libc.so"
    15  //go:cgo_import_dynamic libc_close close "libc.so"
    16  //go:cgo_import_dynamic libc_exit exit "libc.so"
    17  //go:cgo_import_dynamic libc_fstat fstat "libc.so"
    18  //go:cgo_import_dynamic libc_getcontext getcontext "libc.so"
    19  //go:cgo_import_dynamic libc_getrlimit getrlimit "libc.so"
    20  //go:cgo_import_dynamic libc_kill kill "libc.so"
    21  //go:cgo_import_dynamic libc_madvise madvise "libc.so"
    22  //go:cgo_import_dynamic libc_malloc malloc "libc.so"
    23  //go:cgo_import_dynamic libc_mmap mmap "libc.so"
    24  //go:cgo_import_dynamic libc_munmap munmap "libc.so"
    25  //go:cgo_import_dynamic libc_open open "libc.so"
    26  //go:cgo_import_dynamic libc_pthread_attr_destroy pthread_attr_destroy "libc.so"
    27  //go:cgo_import_dynamic libc_pthread_attr_getstack pthread_attr_getstack "libc.so"
    28  //go:cgo_import_dynamic libc_pthread_attr_init pthread_attr_init "libc.so"
    29  //go:cgo_import_dynamic libc_pthread_attr_setdetachstate pthread_attr_setdetachstate "libc.so"
    30  //go:cgo_import_dynamic libc_pthread_attr_setstack pthread_attr_setstack "libc.so"
    31  //go:cgo_import_dynamic libc_pthread_create pthread_create "libc.so"
    32  //go:cgo_import_dynamic libc_raise raise "libc.so"
    33  //go:cgo_import_dynamic libc_read read "libc.so"
    34  //go:cgo_import_dynamic libc_select select "libc.so"
    35  //go:cgo_import_dynamic libc_sched_yield sched_yield "libc.so"
    36  //go:cgo_import_dynamic libc_sem_init sem_init "libc.so"
    37  //go:cgo_import_dynamic libc_sem_post sem_post "libc.so"
    38  //go:cgo_import_dynamic libc_sem_reltimedwait_np sem_reltimedwait_np "libc.so"
    39  //go:cgo_import_dynamic libc_sem_wait sem_wait "libc.so"
    40  //go:cgo_import_dynamic libc_setitimer setitimer "libc.so"
    41  //go:cgo_import_dynamic libc_sigaction sigaction "libc.so"
    42  //go:cgo_import_dynamic libc_sigaltstack sigaltstack "libc.so"
    43  //go:cgo_import_dynamic libc_sigprocmask sigprocmask "libc.so"
    44  //go:cgo_import_dynamic libc_sysconf sysconf "libc.so"
    45  //go:cgo_import_dynamic libc_usleep usleep "libc.so"
    46  //go:cgo_import_dynamic libc_write write "libc.so"
    47  
    48  //go:linkname libc____errno libc____errno
    49  //go:linkname libc_clock_gettime libc_clock_gettime
    50  //go:linkname libc_close libc_close
    51  //go:linkname libc_exit libc_exit
    52  //go:linkname libc_fstat libc_fstat
    53  //go:linkname libc_getcontext libc_getcontext
    54  //go:linkname libc_getrlimit libc_getrlimit
    55  //go:linkname libc_kill libc_kill
    56  //go:linkname libc_madvise libc_madvise
    57  //go:linkname libc_malloc libc_malloc
    58  //go:linkname libc_mmap libc_mmap
    59  //go:linkname libc_munmap libc_munmap
    60  //go:linkname libc_open libc_open
    61  //go:linkname libc_pthread_attr_destroy libc_pthread_attr_destroy
    62  //go:linkname libc_pthread_attr_getstack libc_pthread_attr_getstack
    63  //go:linkname libc_pthread_attr_init libc_pthread_attr_init
    64  //go:linkname libc_pthread_attr_setdetachstate libc_pthread_attr_setdetachstate
    65  //go:linkname libc_pthread_attr_setstack libc_pthread_attr_setstack
    66  //go:linkname libc_pthread_create libc_pthread_create
    67  //go:linkname libc_raise libc_raise
    68  //go:linkname libc_read libc_read
    69  //go:linkname libc_select libc_select
    70  //go:linkname libc_sched_yield libc_sched_yield
    71  //go:linkname libc_sem_init libc_sem_init
    72  //go:linkname libc_sem_post libc_sem_post
    73  //go:linkname libc_sem_reltimedwait_np libc_sem_reltimedwait_np
    74  //go:linkname libc_sem_wait libc_sem_wait
    75  //go:linkname libc_setitimer libc_setitimer
    76  //go:linkname libc_sigaction libc_sigaction
    77  //go:linkname libc_sigaltstack libc_sigaltstack
    78  //go:linkname libc_sigprocmask libc_sigprocmask
    79  //go:linkname libc_sysconf libc_sysconf
    80  //go:linkname libc_usleep libc_usleep
    81  //go:linkname libc_write libc_write
    82  
    83  var (
    84  	libc____errno,
    85  	libc_clock_gettime,
    86  	libc_close,
    87  	libc_exit,
    88  	libc_fstat,
    89  	libc_getcontext,
    90  	libc_getrlimit,
    91  	libc_kill,
    92  	libc_madvise,
    93  	libc_malloc,
    94  	libc_mmap,
    95  	libc_munmap,
    96  	libc_open,
    97  	libc_pthread_attr_destroy,
    98  	libc_pthread_attr_getstack,
    99  	libc_pthread_attr_init,
   100  	libc_pthread_attr_setdetachstate,
   101  	libc_pthread_attr_setstack,
   102  	libc_pthread_create,
   103  	libc_raise,
   104  	libc_read,
   105  	libc_sched_yield,
   106  	libc_select,
   107  	libc_sem_init,
   108  	libc_sem_post,
   109  	libc_sem_reltimedwait_np,
   110  	libc_sem_wait,
   111  	libc_setitimer,
   112  	libc_sigaction,
   113  	libc_sigaltstack,
   114  	libc_sigprocmask,
   115  	libc_sysconf,
   116  	libc_usleep,
   117  	libc_write libcFunc
   118  )
   119  
   120  var sigset_all = sigset{[4]uint32{^uint32(0), ^uint32(0), ^uint32(0), ^uint32(0)}}
   121  
   122  func getncpu() int32 {
   123  	n := int32(sysconf(__SC_NPROCESSORS_ONLN))
   124  	if n < 1 {
   125  		return 1
   126  	}
   127  	return n
   128  }
   129  
   130  func getPageSize() uintptr {
   131  	n := int32(sysconf(__SC_PAGESIZE))
   132  	if n <= 0 {
   133  		return 0
   134  	}
   135  	return uintptr(n)
   136  }
   137  
   138  func osinit() {
   139  	ncpu = getncpu()
   140  	physPageSize = getPageSize()
   141  }
   142  
   143  func tstart_sysvicall(newm *m) uint32
   144  
   145  // May run with m.p==nil, so write barriers are not allowed.
   146  //go:nowritebarrier
   147  func newosproc(mp *m, _ unsafe.Pointer) {
   148  	var (
   149  		attr pthreadattr
   150  		oset sigset
   151  		tid  pthread
   152  		ret  int32
   153  		size uint64
   154  	)
   155  
   156  	if pthread_attr_init(&attr) != 0 {
   157  		throw("pthread_attr_init")
   158  	}
   159  	if pthread_attr_setstack(&attr, 0, 0x200000) != 0 {
   160  		throw("pthread_attr_setstack")
   161  	}
   162  	if pthread_attr_getstack(&attr, unsafe.Pointer(&mp.g0.stack.hi), &size) != 0 {
   163  		throw("pthread_attr_getstack")
   164  	}
   165  	mp.g0.stack.lo = mp.g0.stack.hi - uintptr(size)
   166  	if pthread_attr_setdetachstate(&attr, _PTHREAD_CREATE_DETACHED) != 0 {
   167  		throw("pthread_attr_setdetachstate")
   168  	}
   169  
   170  	// Disable signals during create, so that the new thread starts
   171  	// with signals disabled. It will enable them in minit.
   172  	sigprocmask(_SIG_SETMASK, &sigset_all, &oset)
   173  	ret = pthread_create(&tid, &attr, funcPC(tstart_sysvicall), unsafe.Pointer(mp))
   174  	sigprocmask(_SIG_SETMASK, &oset, nil)
   175  	if ret != 0 {
   176  		print("runtime: failed to create new OS thread (have ", mcount(), " already; errno=", ret, ")\n")
   177  		if ret == -_EAGAIN {
   178  			println("runtime: may need to increase max user processes (ulimit -u)")
   179  		}
   180  		throw("newosproc")
   181  	}
   182  }
   183  
   184  var urandom_dev = []byte("/dev/urandom\x00")
   185  
   186  //go:nosplit
   187  func getRandomData(r []byte) {
   188  	fd := open(&urandom_dev[0], 0 /* O_RDONLY */, 0)
   189  	n := read(fd, unsafe.Pointer(&r[0]), int32(len(r)))
   190  	closefd(fd)
   191  	extendRandom(r, int(n))
   192  }
   193  
   194  func goenvs() {
   195  	goenvs_unix()
   196  }
   197  
   198  // Called to initialize a new m (including the bootstrap m).
   199  // Called on the parent thread (main thread in case of bootstrap), can allocate memory.
   200  func mpreinit(mp *m) {
   201  	mp.gsignal = malg(32 * 1024)
   202  	mp.gsignal.m = mp
   203  }
   204  
   205  func miniterrno()
   206  
   207  // Called to initialize a new m (including the bootstrap m).
   208  // Called on the new thread, cannot allocate memory.
   209  func minit() {
   210  	asmcgocall(unsafe.Pointer(funcPC(miniterrno)), unsafe.Pointer(&libc____errno))
   211  
   212  	minitSignals()
   213  }
   214  
   215  // Called from dropm to undo the effect of an minit.
   216  func unminit() {
   217  	unminitSignals()
   218  }
   219  
   220  func memlimit() uintptr {
   221  	/*
   222  		TODO: Convert to Go when something actually uses the result.
   223  		Rlimit rl;
   224  		extern byte runtime·text[], runtime·end[];
   225  		uintptr used;
   226  
   227  		if(runtime·getrlimit(RLIMIT_AS, &rl) != 0)
   228  			return 0;
   229  		if(rl.rlim_cur >= 0x7fffffff)
   230  			return 0;
   231  
   232  		// Estimate our VM footprint excluding the heap.
   233  		// Not an exact science: use size of binary plus
   234  		// some room for thread stacks.
   235  		used = runtime·end - runtime·text + (64<<20);
   236  		if(used >= rl.rlim_cur)
   237  			return 0;
   238  
   239  		// If there's not at least 16 MB left, we're probably
   240  		// not going to be able to do much. Treat as no limit.
   241  		rl.rlim_cur -= used;
   242  		if(rl.rlim_cur < (16<<20))
   243  			return 0;
   244  
   245  		return rl.rlim_cur - used;
   246  	*/
   247  
   248  	return 0
   249  }
   250  
   251  func sigtramp()
   252  
   253  //go:nosplit
   254  //go:nowritebarrierrec
   255  func setsig(i uint32, fn uintptr) {
   256  	var sa sigactiont
   257  
   258  	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK | _SA_RESTART
   259  	sa.sa_mask = sigset_all
   260  	if fn == funcPC(sighandler) {
   261  		fn = funcPC(sigtramp)
   262  	}
   263  	*((*uintptr)(unsafe.Pointer(&sa._funcptr))) = fn
   264  	sigaction(i, &sa, nil)
   265  }
   266  
   267  //go:nosplit
   268  //go:nowritebarrierrec
   269  func setsigstack(i uint32) {
   270  	var sa sigactiont
   271  	sigaction(i, nil, &sa)
   272  	if sa.sa_flags&_SA_ONSTACK != 0 {
   273  		return
   274  	}
   275  	sa.sa_flags |= _SA_ONSTACK
   276  	sigaction(i, &sa, nil)
   277  }
   278  
   279  //go:nosplit
   280  //go:nowritebarrierrec
   281  func getsig(i uint32) uintptr {
   282  	var sa sigactiont
   283  	sigaction(i, nil, &sa)
   284  	return *((*uintptr)(unsafe.Pointer(&sa._funcptr)))
   285  }
   286  
   287  // setSignaltstackSP sets the ss_sp field of a stackt.
   288  //go:nosplit
   289  func setSignalstackSP(s *stackt, sp uintptr) {
   290  	*(*uintptr)(unsafe.Pointer(&s.ss_sp)) = sp
   291  }
   292  
   293  //go:nosplit
   294  //go:nowritebarrierrec
   295  func sigaddset(mask *sigset, i int) {
   296  	mask.__sigbits[(i-1)/32] |= 1 << ((uint32(i) - 1) & 31)
   297  }
   298  
   299  func sigdelset(mask *sigset, i int) {
   300  	mask.__sigbits[(i-1)/32] &^= 1 << ((uint32(i) - 1) & 31)
   301  }
   302  
   303  func (c *sigctxt) fixsigcode(sig uint32) {
   304  }
   305  
   306  //go:nosplit
   307  func semacreate(mp *m) {
   308  	if mp.waitsema != 0 {
   309  		return
   310  	}
   311  
   312  	var sem *semt
   313  	_g_ := getg()
   314  
   315  	// Call libc's malloc rather than malloc. This will
   316  	// allocate space on the C heap. We can't call malloc
   317  	// here because it could cause a deadlock.
   318  	_g_.m.libcall.fn = uintptr(unsafe.Pointer(&libc_malloc))
   319  	_g_.m.libcall.n = 1
   320  	_g_.m.scratch = mscratch{}
   321  	_g_.m.scratch.v[0] = unsafe.Sizeof(*sem)
   322  	_g_.m.libcall.args = uintptr(unsafe.Pointer(&_g_.m.scratch))
   323  	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&_g_.m.libcall))
   324  	sem = (*semt)(unsafe.Pointer(_g_.m.libcall.r1))
   325  	if sem_init(sem, 0, 0) != 0 {
   326  		throw("sem_init")
   327  	}
   328  	mp.waitsema = uintptr(unsafe.Pointer(sem))
   329  }
   330  
   331  //go:nosplit
   332  func semasleep(ns int64) int32 {
   333  	_m_ := getg().m
   334  	if ns >= 0 {
   335  		_m_.ts.tv_sec = ns / 1000000000
   336  		_m_.ts.tv_nsec = ns % 1000000000
   337  
   338  		_m_.libcall.fn = uintptr(unsafe.Pointer(&libc_sem_reltimedwait_np))
   339  		_m_.libcall.n = 2
   340  		_m_.scratch = mscratch{}
   341  		_m_.scratch.v[0] = _m_.waitsema
   342  		_m_.scratch.v[1] = uintptr(unsafe.Pointer(&_m_.ts))
   343  		_m_.libcall.args = uintptr(unsafe.Pointer(&_m_.scratch))
   344  		asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&_m_.libcall))
   345  		if *_m_.perrno != 0 {
   346  			if *_m_.perrno == _ETIMEDOUT || *_m_.perrno == _EAGAIN || *_m_.perrno == _EINTR {
   347  				return -1
   348  			}
   349  			throw("sem_reltimedwait_np")
   350  		}
   351  		return 0
   352  	}
   353  	for {
   354  		_m_.libcall.fn = uintptr(unsafe.Pointer(&libc_sem_wait))
   355  		_m_.libcall.n = 1
   356  		_m_.scratch = mscratch{}
   357  		_m_.scratch.v[0] = _m_.waitsema
   358  		_m_.libcall.args = uintptr(unsafe.Pointer(&_m_.scratch))
   359  		asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&_m_.libcall))
   360  		if _m_.libcall.r1 == 0 {
   361  			break
   362  		}
   363  		if *_m_.perrno == _EINTR {
   364  			continue
   365  		}
   366  		throw("sem_wait")
   367  	}
   368  	return 0
   369  }
   370  
   371  //go:nosplit
   372  func semawakeup(mp *m) {
   373  	if sem_post((*semt)(unsafe.Pointer(mp.waitsema))) != 0 {
   374  		throw("sem_post")
   375  	}
   376  }
   377  
   378  //go:nosplit
   379  func closefd(fd int32) int32 {
   380  	return int32(sysvicall1(&libc_close, uintptr(fd)))
   381  }
   382  
   383  //go:nosplit
   384  func exit(r int32) {
   385  	sysvicall1(&libc_exit, uintptr(r))
   386  }
   387  
   388  //go:nosplit
   389  func getcontext(context *ucontext) /* int32 */ {
   390  	sysvicall1(&libc_getcontext, uintptr(unsafe.Pointer(context)))
   391  }
   392  
   393  //go:nosplit
   394  func madvise(addr unsafe.Pointer, n uintptr, flags int32) {
   395  	sysvicall3(&libc_madvise, uintptr(addr), uintptr(n), uintptr(flags))
   396  }
   397  
   398  //go:nosplit
   399  func mmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uint32) unsafe.Pointer {
   400  	p, err := doMmap(uintptr(addr), n, uintptr(prot), uintptr(flags), uintptr(fd), uintptr(off))
   401  	if p == ^uintptr(0) {
   402  		return unsafe.Pointer(err)
   403  	}
   404  	return unsafe.Pointer(p)
   405  }
   406  
   407  //go:nosplit
   408  func doMmap(addr, n, prot, flags, fd, off uintptr) (uintptr, uintptr) {
   409  	var libcall libcall
   410  	libcall.fn = uintptr(unsafe.Pointer(&libc_mmap))
   411  	libcall.n = 6
   412  	libcall.args = uintptr(noescape(unsafe.Pointer(&addr)))
   413  	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&libcall))
   414  	return libcall.r1, libcall.err
   415  }
   416  
   417  //go:nosplit
   418  func munmap(addr unsafe.Pointer, n uintptr) {
   419  	sysvicall2(&libc_munmap, uintptr(addr), uintptr(n))
   420  }
   421  
   422  func nanotime1()
   423  
   424  //go:nosplit
   425  func nanotime() int64 {
   426  	return int64(sysvicall0((*libcFunc)(unsafe.Pointer(funcPC(nanotime1)))))
   427  }
   428  
   429  //go:nosplit
   430  func open(path *byte, mode, perm int32) int32 {
   431  	return int32(sysvicall3(&libc_open, uintptr(unsafe.Pointer(path)), uintptr(mode), uintptr(perm)))
   432  }
   433  
   434  func pthread_attr_destroy(attr *pthreadattr) int32 {
   435  	return int32(sysvicall1(&libc_pthread_attr_destroy, uintptr(unsafe.Pointer(attr))))
   436  }
   437  
   438  func pthread_attr_getstack(attr *pthreadattr, addr unsafe.Pointer, size *uint64) int32 {
   439  	return int32(sysvicall3(&libc_pthread_attr_getstack, uintptr(unsafe.Pointer(attr)), uintptr(addr), uintptr(unsafe.Pointer(size))))
   440  }
   441  
   442  func pthread_attr_init(attr *pthreadattr) int32 {
   443  	return int32(sysvicall1(&libc_pthread_attr_init, uintptr(unsafe.Pointer(attr))))
   444  }
   445  
   446  func pthread_attr_setdetachstate(attr *pthreadattr, state int32) int32 {
   447  	return int32(sysvicall2(&libc_pthread_attr_setdetachstate, uintptr(unsafe.Pointer(attr)), uintptr(state)))
   448  }
   449  
   450  func pthread_attr_setstack(attr *pthreadattr, addr uintptr, size uint64) int32 {
   451  	return int32(sysvicall3(&libc_pthread_attr_setstack, uintptr(unsafe.Pointer(attr)), uintptr(addr), uintptr(size)))
   452  }
   453  
   454  func pthread_create(thread *pthread, attr *pthreadattr, fn uintptr, arg unsafe.Pointer) int32 {
   455  	return int32(sysvicall4(&libc_pthread_create, uintptr(unsafe.Pointer(thread)), uintptr(unsafe.Pointer(attr)), uintptr(fn), uintptr(arg)))
   456  }
   457  
   458  //go:nosplit
   459  //go:nowritebarrierrec
   460  func raise(sig uint32) /* int32 */ {
   461  	sysvicall1(&libc_raise, uintptr(sig))
   462  }
   463  
   464  func raiseproc(sig uint32) /* int32 */ {
   465  	pid := sysvicall0(&libc_getpid)
   466  	sysvicall2(&libc_kill, pid, uintptr(sig))
   467  }
   468  
   469  //go:nosplit
   470  func read(fd int32, buf unsafe.Pointer, nbyte int32) int32 {
   471  	return int32(sysvicall3(&libc_read, uintptr(fd), uintptr(buf), uintptr(nbyte)))
   472  }
   473  
   474  //go:nosplit
   475  func sem_init(sem *semt, pshared int32, value uint32) int32 {
   476  	return int32(sysvicall3(&libc_sem_init, uintptr(unsafe.Pointer(sem)), uintptr(pshared), uintptr(value)))
   477  }
   478  
   479  //go:nosplit
   480  func sem_post(sem *semt) int32 {
   481  	return int32(sysvicall1(&libc_sem_post, uintptr(unsafe.Pointer(sem))))
   482  }
   483  
   484  //go:nosplit
   485  func sem_reltimedwait_np(sem *semt, timeout *timespec) int32 {
   486  	return int32(sysvicall2(&libc_sem_reltimedwait_np, uintptr(unsafe.Pointer(sem)), uintptr(unsafe.Pointer(timeout))))
   487  }
   488  
   489  //go:nosplit
   490  func sem_wait(sem *semt) int32 {
   491  	return int32(sysvicall1(&libc_sem_wait, uintptr(unsafe.Pointer(sem))))
   492  }
   493  
   494  func setitimer(which int32, value *itimerval, ovalue *itimerval) /* int32 */ {
   495  	sysvicall3(&libc_setitimer, uintptr(which), uintptr(unsafe.Pointer(value)), uintptr(unsafe.Pointer(ovalue)))
   496  }
   497  
   498  //go:nosplit
   499  //go:nowritebarrierrec
   500  func sigaction(sig uint32, act *sigactiont, oact *sigactiont) /* int32 */ {
   501  	sysvicall3(&libc_sigaction, uintptr(sig), uintptr(unsafe.Pointer(act)), uintptr(unsafe.Pointer(oact)))
   502  }
   503  
   504  //go:nosplit
   505  //go:nowritebarrierrec
   506  func sigaltstack(ss *stackt, oss *stackt) /* int32 */ {
   507  	sysvicall2(&libc_sigaltstack, uintptr(unsafe.Pointer(ss)), uintptr(unsafe.Pointer(oss)))
   508  }
   509  
   510  //go:nosplit
   511  //go:nowritebarrierrec
   512  func sigprocmask(how int32, set *sigset, oset *sigset) /* int32 */ {
   513  	sysvicall3(&libc_sigprocmask, uintptr(how), uintptr(unsafe.Pointer(set)), uintptr(unsafe.Pointer(oset)))
   514  }
   515  
   516  func sysconf(name int32) int64 {
   517  	return int64(sysvicall1(&libc_sysconf, uintptr(name)))
   518  }
   519  
   520  func usleep1(usec uint32)
   521  
   522  //go:nosplit
   523  func usleep(µs uint32) {
   524  	usleep1(µs)
   525  }
   526  
   527  //go:nosplit
   528  func write(fd uintptr, buf unsafe.Pointer, nbyte int32) int32 {
   529  	return int32(sysvicall3(&libc_write, uintptr(fd), uintptr(buf), uintptr(nbyte)))
   530  }
   531  
   532  func osyield1()
   533  
   534  //go:nosplit
   535  func osyield() {
   536  	_g_ := getg()
   537  
   538  	// Check the validity of m because we might be called in cgo callback
   539  	// path early enough where there isn't a m available yet.
   540  	if _g_ != nil && _g_.m != nil {
   541  		sysvicall0(&libc_sched_yield)
   542  		return
   543  	}
   544  	osyield1()
   545  }