Source file src/runtime/os_linux.go

Documentation: runtime

     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  package runtime
     6  
     7  import (
     8  	"internal/abi"
     9  	"internal/goarch"
    10  	"runtime/internal/atomic"
    11  	"runtime/internal/syscall"
    12  	"unsafe"
    13  )
    14  
    15  // sigPerThreadSyscall is the same signal (SIGSETXID) used by glibc for
    16  // per-thread syscalls on Linux. We use it for the same purpose in non-cgo
    17  // binaries.
    18  const sigPerThreadSyscall = _SIGRTMIN + 1
    19  
    20  type mOS struct {
    21  	// profileTimer holds the ID of the POSIX interval timer for profiling CPU
    22  	// usage on this thread.
    23  	//
    24  	// It is valid when the profileTimerValid field is non-zero. A thread
    25  	// creates and manages its own timer, and these fields are read and written
    26  	// only by this thread. But because some of the reads on profileTimerValid
    27  	// are in signal handling code, access to that field uses atomic operations.
    28  	profileTimer      int32
    29  	profileTimerValid uint32
    30  
    31  	// needPerThreadSyscall indicates that a per-thread syscall is required
    32  	// for doAllThreadsSyscall.
    33  	needPerThreadSyscall atomic.Uint8
    34  }
    35  
    36  //go:noescape
    37  func futex(addr unsafe.Pointer, op int32, val uint32, ts, addr2 unsafe.Pointer, val3 uint32) int32
    38  
    39  // Linux futex.
    40  //
    41  //	futexsleep(uint32 *addr, uint32 val)
    42  //	futexwakeup(uint32 *addr)
    43  //
    44  // Futexsleep atomically checks if *addr == val and if so, sleeps on addr.
    45  // Futexwakeup wakes up threads sleeping on addr.
    46  // Futexsleep is allowed to wake up spuriously.
    47  
    48  const (
    49  	_FUTEX_PRIVATE_FLAG = 128
    50  	_FUTEX_WAIT_PRIVATE = 0 | _FUTEX_PRIVATE_FLAG
    51  	_FUTEX_WAKE_PRIVATE = 1 | _FUTEX_PRIVATE_FLAG
    52  )
    53  
    54  // Atomically,
    55  //
    56  //	if(*addr == val) sleep
    57  //
    58  // Might be woken up spuriously; that's allowed.
    59  // Don't sleep longer than ns; ns < 0 means forever.
    60  //
    61  //go:nosplit
    62  func futexsleep(addr *uint32, val uint32, ns int64) {
    63  	// Some Linux kernels have a bug where futex of
    64  	// FUTEX_WAIT returns an internal error code
    65  	// as an errno. Libpthread ignores the return value
    66  	// here, and so can we: as it says a few lines up,
    67  	// spurious wakeups are allowed.
    68  	if ns < 0 {
    69  		futex(unsafe.Pointer(addr), _FUTEX_WAIT_PRIVATE, val, nil, nil, 0)
    70  		return
    71  	}
    72  
    73  	var ts timespec
    74  	ts.setNsec(ns)
    75  	futex(unsafe.Pointer(addr), _FUTEX_WAIT_PRIVATE, val, unsafe.Pointer(&ts), nil, 0)
    76  }
    77  
    78  // If any procs are sleeping on addr, wake up at most cnt.
    79  //
    80  //go:nosplit
    81  func futexwakeup(addr *uint32, cnt uint32) {
    82  	ret := futex(unsafe.Pointer(addr), _FUTEX_WAKE_PRIVATE, cnt, nil, nil, 0)
    83  	if ret >= 0 {
    84  		return
    85  	}
    86  
    87  	// I don't know that futex wakeup can return
    88  	// EAGAIN or EINTR, but if it does, it would be
    89  	// safe to loop and call futex again.
    90  	systemstack(func() {
    91  		print("futexwakeup addr=", addr, " returned ", ret, "\n")
    92  	})
    93  
    94  	*(*int32)(unsafe.Pointer(uintptr(0x1006))) = 0x1006
    95  }
    96  
    97  func getproccount() int32 {
    98  	// This buffer is huge (8 kB) but we are on the system stack
    99  	// and there should be plenty of space (64 kB).
   100  	// Also this is a leaf, so we're not holding up the memory for long.
   101  	// See golang.org/issue/11823.
   102  	// The suggested behavior here is to keep trying with ever-larger
   103  	// buffers, but we don't have a dynamic memory allocator at the
   104  	// moment, so that's a bit tricky and seems like overkill.
   105  	const maxCPUs = 64 * 1024
   106  	var buf [maxCPUs / 8]byte
   107  	r := sched_getaffinity(0, unsafe.Sizeof(buf), &buf[0])
   108  	if r < 0 {
   109  		return 1
   110  	}
   111  	n := int32(0)
   112  	for _, v := range buf[:r] {
   113  		for v != 0 {
   114  			n += int32(v & 1)
   115  			v >>= 1
   116  		}
   117  	}
   118  	if n == 0 {
   119  		n = 1
   120  	}
   121  	return n
   122  }
   123  
   124  // Clone, the Linux rfork.
   125  const (
   126  	_CLONE_VM             = 0x100
   127  	_CLONE_FS             = 0x200
   128  	_CLONE_FILES          = 0x400
   129  	_CLONE_SIGHAND        = 0x800
   130  	_CLONE_PTRACE         = 0x2000
   131  	_CLONE_VFORK          = 0x4000
   132  	_CLONE_PARENT         = 0x8000
   133  	_CLONE_THREAD         = 0x10000
   134  	_CLONE_NEWNS          = 0x20000
   135  	_CLONE_SYSVSEM        = 0x40000
   136  	_CLONE_SETTLS         = 0x80000
   137  	_CLONE_PARENT_SETTID  = 0x100000
   138  	_CLONE_CHILD_CLEARTID = 0x200000
   139  	_CLONE_UNTRACED       = 0x800000
   140  	_CLONE_CHILD_SETTID   = 0x1000000
   141  	_CLONE_STOPPED        = 0x2000000
   142  	_CLONE_NEWUTS         = 0x4000000
   143  	_CLONE_NEWIPC         = 0x8000000
   144  
   145  	// As of QEMU 2.8.0 (5ea2fc84d), user emulation requires all six of these
   146  	// flags to be set when creating a thread; attempts to share the other
   147  	// five but leave SYSVSEM unshared will fail with -EINVAL.
   148  	//
   149  	// In non-QEMU environments CLONE_SYSVSEM is inconsequential as we do not
   150  	// use System V semaphores.
   151  
   152  	cloneFlags = _CLONE_VM | /* share memory */
   153  		_CLONE_FS | /* share cwd, etc */
   154  		_CLONE_FILES | /* share fd table */
   155  		_CLONE_SIGHAND | /* share sig handler table */
   156  		_CLONE_SYSVSEM | /* share SysV semaphore undo lists (see issue #20763) */
   157  		_CLONE_THREAD /* revisit - okay for now */
   158  )
   159  
   160  //go:noescape
   161  func clone(flags int32, stk, mp, gp, fn unsafe.Pointer) int32
   162  
   163  // May run with m.p==nil, so write barriers are not allowed.
   164  //
   165  //go:nowritebarrier
   166  func newosproc(mp *m) {
   167  	stk := unsafe.Pointer(mp.g0.stack.hi)
   168  	/*
   169  	 * note: strace gets confused if we use CLONE_PTRACE here.
   170  	 */
   171  	if false {
   172  		print("newosproc stk=", stk, " m=", mp, " g=", mp.g0, " clone=", abi.FuncPCABI0(clone), " id=", mp.id, " ostk=", &mp, "\n")
   173  	}
   174  
   175  	// Disable signals during clone, so that the new thread starts
   176  	// with signals disabled. It will enable them in minit.
   177  	var oset sigset
   178  	sigprocmask(_SIG_SETMASK, &sigset_all, &oset)
   179  	ret := clone(cloneFlags, stk, unsafe.Pointer(mp), unsafe.Pointer(mp.g0), unsafe.Pointer(abi.FuncPCABI0(mstart)))
   180  	sigprocmask(_SIG_SETMASK, &oset, nil)
   181  
   182  	if ret < 0 {
   183  		print("runtime: failed to create new OS thread (have ", mcount(), " already; errno=", -ret, ")\n")
   184  		if ret == -_EAGAIN {
   185  			println("runtime: may need to increase max user processes (ulimit -u)")
   186  		}
   187  		throw("newosproc")
   188  	}
   189  }
   190  
   191  // Version of newosproc that doesn't require a valid G.
   192  //
   193  //go:nosplit
   194  func newosproc0(stacksize uintptr, fn unsafe.Pointer) {
   195  	stack := sysAlloc(stacksize, &memstats.stacks_sys)
   196  	if stack == nil {
   197  		write(2, unsafe.Pointer(&failallocatestack[0]), int32(len(failallocatestack)))
   198  		exit(1)
   199  	}
   200  	ret := clone(cloneFlags, unsafe.Pointer(uintptr(stack)+stacksize), nil, nil, fn)
   201  	if ret < 0 {
   202  		write(2, unsafe.Pointer(&failthreadcreate[0]), int32(len(failthreadcreate)))
   203  		exit(1)
   204  	}
   205  }
   206  
   207  var failallocatestack = []byte("runtime: failed to allocate stack for the new OS thread\n")
   208  var failthreadcreate = []byte("runtime: failed to create new OS thread\n")
   209  
   210  const (
   211  	_AT_NULL   = 0  // End of vector
   212  	_AT_PAGESZ = 6  // System physical page size
   213  	_AT_HWCAP  = 16 // hardware capability bit vector
   214  	_AT_RANDOM = 25 // introduced in 2.6.29
   215  	_AT_HWCAP2 = 26 // hardware capability bit vector 2
   216  )
   217  
   218  var procAuxv = []byte("/proc/self/auxv\x00")
   219  
   220  var addrspace_vec [1]byte
   221  
   222  func mincore(addr unsafe.Pointer, n uintptr, dst *byte) int32
   223  
   224  func sysargs(argc int32, argv **byte) {
   225  	n := argc + 1
   226  
   227  	// skip over argv, envp to get to auxv
   228  	for argv_index(argv, n) != nil {
   229  		n++
   230  	}
   231  
   232  	// skip NULL separator
   233  	n++
   234  
   235  	// now argv+n is auxv
   236  	auxv := (*[1 << 28]uintptr)(add(unsafe.Pointer(argv), uintptr(n)*goarch.PtrSize))
   237  	if sysauxv(auxv[:]) != 0 {
   238  		return
   239  	}
   240  	// In some situations we don't get a loader-provided
   241  	// auxv, such as when loaded as a library on Android.
   242  	// Fall back to /proc/self/auxv.
   243  	fd := open(&procAuxv[0], 0 /* O_RDONLY */, 0)
   244  	if fd < 0 {
   245  		// On Android, /proc/self/auxv might be unreadable (issue 9229), so we fallback to
   246  		// try using mincore to detect the physical page size.
   247  		// mincore should return EINVAL when address is not a multiple of system page size.
   248  		const size = 256 << 10 // size of memory region to allocate
   249  		p, err := mmap(nil, size, _PROT_READ|_PROT_WRITE, _MAP_ANON|_MAP_PRIVATE, -1, 0)
   250  		if err != 0 {
   251  			return
   252  		}
   253  		var n uintptr
   254  		for n = 4 << 10; n < size; n <<= 1 {
   255  			err := mincore(unsafe.Pointer(uintptr(p)+n), 1, &addrspace_vec[0])
   256  			if err == 0 {
   257  				physPageSize = n
   258  				break
   259  			}
   260  		}
   261  		if physPageSize == 0 {
   262  			physPageSize = size
   263  		}
   264  		munmap(p, size)
   265  		return
   266  	}
   267  	var buf [128]uintptr
   268  	n = read(fd, noescape(unsafe.Pointer(&buf[0])), int32(unsafe.Sizeof(buf)))
   269  	closefd(fd)
   270  	if n < 0 {
   271  		return
   272  	}
   273  	// Make sure buf is terminated, even if we didn't read
   274  	// the whole file.
   275  	buf[len(buf)-2] = _AT_NULL
   276  	sysauxv(buf[:])
   277  }
   278  
   279  // startupRandomData holds random bytes initialized at startup. These come from
   280  // the ELF AT_RANDOM auxiliary vector.
   281  var startupRandomData []byte
   282  
   283  func sysauxv(auxv []uintptr) int {
   284  	var i int
   285  	for ; auxv[i] != _AT_NULL; i += 2 {
   286  		tag, val := auxv[i], auxv[i+1]
   287  		switch tag {
   288  		case _AT_RANDOM:
   289  			// The kernel provides a pointer to 16-bytes
   290  			// worth of random data.
   291  			startupRandomData = (*[16]byte)(unsafe.Pointer(val))[:]
   292  
   293  		case _AT_PAGESZ:
   294  			physPageSize = val
   295  		}
   296  
   297  		archauxv(tag, val)
   298  		vdsoauxv(tag, val)
   299  	}
   300  	return i / 2
   301  }
   302  
   303  var sysTHPSizePath = []byte("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size\x00")
   304  
   305  func getHugePageSize() uintptr {
   306  	var numbuf [20]byte
   307  	fd := open(&sysTHPSizePath[0], 0 /* O_RDONLY */, 0)
   308  	if fd < 0 {
   309  		return 0
   310  	}
   311  	ptr := noescape(unsafe.Pointer(&numbuf[0]))
   312  	n := read(fd, ptr, int32(len(numbuf)))
   313  	closefd(fd)
   314  	if n <= 0 {
   315  		return 0
   316  	}
   317  	n-- // remove trailing newline
   318  	v, ok := atoi(slicebytetostringtmp((*byte)(ptr), int(n)))
   319  	if !ok || v < 0 {
   320  		v = 0
   321  	}
   322  	if v&(v-1) != 0 {
   323  		// v is not a power of 2
   324  		return 0
   325  	}
   326  	return uintptr(v)
   327  }
   328  
   329  func osinit() {
   330  	ncpu = getproccount()
   331  	physHugePageSize = getHugePageSize()
   332  	if iscgo {
   333  		// #42494 glibc and musl reserve some signals for
   334  		// internal use and require they not be blocked by
   335  		// the rest of a normal C runtime. When the go runtime
   336  		// blocks...unblocks signals, temporarily, the blocked
   337  		// interval of time is generally very short. As such,
   338  		// these expectations of *libc code are mostly met by
   339  		// the combined go+cgo system of threads. However,
   340  		// when go causes a thread to exit, via a return from
   341  		// mstart(), the combined runtime can deadlock if
   342  		// these signals are blocked. Thus, don't block these
   343  		// signals when exiting threads.
   344  		// - glibc: SIGCANCEL (32), SIGSETXID (33)
   345  		// - musl: SIGTIMER (32), SIGCANCEL (33), SIGSYNCCALL (34)
   346  		sigdelset(&sigsetAllExiting, 32)
   347  		sigdelset(&sigsetAllExiting, 33)
   348  		sigdelset(&sigsetAllExiting, 34)
   349  	}
   350  	osArchInit()
   351  }
   352  
   353  var urandom_dev = []byte("/dev/urandom\x00")
   354  
   355  func getRandomData(r []byte) {
   356  	if startupRandomData != nil {
   357  		n := copy(r, startupRandomData)
   358  		extendRandom(r, n)
   359  		return
   360  	}
   361  	fd := open(&urandom_dev[0], 0 /* O_RDONLY */, 0)
   362  	n := read(fd, unsafe.Pointer(&r[0]), int32(len(r)))
   363  	closefd(fd)
   364  	extendRandom(r, int(n))
   365  }
   366  
   367  func goenvs() {
   368  	goenvs_unix()
   369  }
   370  
   371  // Called to do synchronous initialization of Go code built with
   372  // -buildmode=c-archive or -buildmode=c-shared.
   373  // None of the Go runtime is initialized.
   374  //
   375  //go:nosplit
   376  //go:nowritebarrierrec
   377  func libpreinit() {
   378  	initsig(true)
   379  }
   380  
   381  // Called to initialize a new m (including the bootstrap m).
   382  // Called on the parent thread (main thread in case of bootstrap), can allocate memory.
   383  func mpreinit(mp *m) {
   384  	mp.gsignal = malg(32 * 1024) // Linux wants >= 2K
   385  	mp.gsignal.m = mp
   386  }
   387  
   388  func gettid() uint32
   389  
   390  // Called to initialize a new m (including the bootstrap m).
   391  // Called on the new thread, cannot allocate memory.
   392  func minit() {
   393  	minitSignals()
   394  
   395  	// Cgo-created threads and the bootstrap m are missing a
   396  	// procid. We need this for asynchronous preemption and it's
   397  	// useful in debuggers.
   398  	getg().m.procid = uint64(gettid())
   399  }
   400  
   401  // Called from dropm to undo the effect of an minit.
   402  //
   403  //go:nosplit
   404  func unminit() {
   405  	unminitSignals()
   406  }
   407  
   408  // Called from exitm, but not from drop, to undo the effect of thread-owned
   409  // resources in minit, semacreate, or elsewhere. Do not take locks after calling this.
   410  func mdestroy(mp *m) {
   411  }
   412  
   413  //#ifdef GOARCH_386
   414  //#define sa_handler k_sa_handler
   415  //#endif
   416  
   417  func sigreturn()
   418  func sigtramp() // Called via C ABI
   419  func cgoSigtramp()
   420  
   421  //go:noescape
   422  func sigaltstack(new, old *stackt)
   423  
   424  //go:noescape
   425  func setitimer(mode int32, new, old *itimerval)
   426  
   427  //go:noescape
   428  func timer_create(clockid int32, sevp *sigevent, timerid *int32) int32
   429  
   430  //go:noescape
   431  func timer_settime(timerid int32, flags int32, new, old *itimerspec) int32
   432  
   433  //go:noescape
   434  func timer_delete(timerid int32) int32
   435  
   436  //go:noescape
   437  func rtsigprocmask(how int32, new, old *sigset, size int32)
   438  
   439  //go:nosplit
   440  //go:nowritebarrierrec
   441  func sigprocmask(how int32, new, old *sigset) {
   442  	rtsigprocmask(how, new, old, int32(unsafe.Sizeof(*new)))
   443  }
   444  
   445  func raise(sig uint32)
   446  func raiseproc(sig uint32)
   447  
   448  //go:noescape
   449  func sched_getaffinity(pid, len uintptr, buf *byte) int32
   450  func osyield()
   451  
   452  //go:nosplit
   453  func osyield_no_g() {
   454  	osyield()
   455  }
   456  
   457  func pipe2(flags int32) (r, w int32, errno int32)
   458  
   459  const (
   460  	_si_max_size    = 128
   461  	_sigev_max_size = 64
   462  )
   463  
   464  //go:nosplit
   465  //go:nowritebarrierrec
   466  func setsig(i uint32, fn uintptr) {
   467  	var sa sigactiont
   468  	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK | _SA_RESTORER | _SA_RESTART
   469  	sigfillset(&sa.sa_mask)
   470  	// Although Linux manpage says "sa_restorer element is obsolete and
   471  	// should not be used". x86_64 kernel requires it. Only use it on
   472  	// x86.
   473  	if GOARCH == "386" || GOARCH == "amd64" {
   474  		sa.sa_restorer = abi.FuncPCABI0(sigreturn)
   475  	}
   476  	if fn == abi.FuncPCABIInternal(sighandler) { // abi.FuncPCABIInternal(sighandler) matches the callers in signal_unix.go
   477  		if iscgo {
   478  			fn = abi.FuncPCABI0(cgoSigtramp)
   479  		} else {
   480  			fn = abi.FuncPCABI0(sigtramp)
   481  		}
   482  	}
   483  	sa.sa_handler = fn
   484  	sigaction(i, &sa, nil)
   485  }
   486  
   487  //go:nosplit
   488  //go:nowritebarrierrec
   489  func setsigstack(i uint32) {
   490  	var sa sigactiont
   491  	sigaction(i, nil, &sa)
   492  	if sa.sa_flags&_SA_ONSTACK != 0 {
   493  		return
   494  	}
   495  	sa.sa_flags |= _SA_ONSTACK
   496  	sigaction(i, &sa, nil)
   497  }
   498  
   499  //go:nosplit
   500  //go:nowritebarrierrec
   501  func getsig(i uint32) uintptr {
   502  	var sa sigactiont
   503  	sigaction(i, nil, &sa)
   504  	return sa.sa_handler
   505  }
   506  
   507  // setSignaltstackSP sets the ss_sp field of a stackt.
   508  //
   509  //go:nosplit
   510  func setSignalstackSP(s *stackt, sp uintptr) {
   511  	*(*uintptr)(unsafe.Pointer(&s.ss_sp)) = sp
   512  }
   513  
   514  //go:nosplit
   515  func (c *sigctxt) fixsigcode(sig uint32) {
   516  }
   517  
   518  // sysSigaction calls the rt_sigaction system call.
   519  //
   520  //go:nosplit
   521  func sysSigaction(sig uint32, new, old *sigactiont) {
   522  	if rt_sigaction(uintptr(sig), new, old, unsafe.Sizeof(sigactiont{}.sa_mask)) != 0 {
   523  		// Workaround for bugs in QEMU user mode emulation.
   524  		//
   525  		// QEMU turns calls to the sigaction system call into
   526  		// calls to the C library sigaction call; the C
   527  		// library call rejects attempts to call sigaction for
   528  		// SIGCANCEL (32) or SIGSETXID (33).
   529  		//
   530  		// QEMU rejects calling sigaction on SIGRTMAX (64).
   531  		//
   532  		// Just ignore the error in these case. There isn't
   533  		// anything we can do about it anyhow.
   534  		if sig != 32 && sig != 33 && sig != 64 {
   535  			// Use system stack to avoid split stack overflow on ppc64/ppc64le.
   536  			systemstack(func() {
   537  				throw("sigaction failed")
   538  			})
   539  		}
   540  	}
   541  }
   542  
   543  // rt_sigaction is implemented in assembly.
   544  //
   545  //go:noescape
   546  func rt_sigaction(sig uintptr, new, old *sigactiont, size uintptr) int32
   547  
   548  func getpid() int
   549  func tgkill(tgid, tid, sig int)
   550  
   551  // signalM sends a signal to mp.
   552  func signalM(mp *m, sig int) {
   553  	tgkill(getpid(), int(mp.procid), sig)
   554  }
   555  
   556  // go118UseTimerCreateProfiler enables the per-thread CPU profiler.
   557  const go118UseTimerCreateProfiler = true
   558  
   559  // validSIGPROF compares this signal delivery's code against the signal sources
   560  // that the profiler uses, returning whether the delivery should be processed.
   561  // To be processed, a signal delivery from a known profiling mechanism should
   562  // correspond to the best profiling mechanism available to this thread. Signals
   563  // from other sources are always considered valid.
   564  //
   565  //go:nosplit
   566  func validSIGPROF(mp *m, c *sigctxt) bool {
   567  	code := int32(c.sigcode())
   568  	setitimer := code == _SI_KERNEL
   569  	timer_create := code == _SI_TIMER
   570  
   571  	if !(setitimer || timer_create) {
   572  		// The signal doesn't correspond to a profiling mechanism that the
   573  		// runtime enables itself. There's no reason to process it, but there's
   574  		// no reason to ignore it either.
   575  		return true
   576  	}
   577  
   578  	if mp == nil {
   579  		// Since we don't have an M, we can't check if there's an active
   580  		// per-thread timer for this thread. We don't know how long this thread
   581  		// has been around, and if it happened to interact with the Go scheduler
   582  		// at a time when profiling was active (causing it to have a per-thread
   583  		// timer). But it may have never interacted with the Go scheduler, or
   584  		// never while profiling was active. To avoid double-counting, process
   585  		// only signals from setitimer.
   586  		//
   587  		// When a custom cgo traceback function has been registered (on
   588  		// platforms that support runtime.SetCgoTraceback), SIGPROF signals
   589  		// delivered to a thread that cannot find a matching M do this check in
   590  		// the assembly implementations of runtime.cgoSigtramp.
   591  		return setitimer
   592  	}
   593  
   594  	// Having an M means the thread interacts with the Go scheduler, and we can
   595  	// check whether there's an active per-thread timer for this thread.
   596  	if atomic.Load(&mp.profileTimerValid) != 0 {
   597  		// If this M has its own per-thread CPU profiling interval timer, we
   598  		// should track the SIGPROF signals that come from that timer (for
   599  		// accurate reporting of its CPU usage; see issue 35057) and ignore any
   600  		// that it gets from the process-wide setitimer (to not over-count its
   601  		// CPU consumption).
   602  		return timer_create
   603  	}
   604  
   605  	// No active per-thread timer means the only valid profiler is setitimer.
   606  	return setitimer
   607  }
   608  
   609  func setProcessCPUProfiler(hz int32) {
   610  	setProcessCPUProfilerTimer(hz)
   611  }
   612  
   613  func setThreadCPUProfiler(hz int32) {
   614  	mp := getg().m
   615  	mp.profilehz = hz
   616  
   617  	if !go118UseTimerCreateProfiler {
   618  		return
   619  	}
   620  
   621  	// destroy any active timer
   622  	if atomic.Load(&mp.profileTimerValid) != 0 {
   623  		timerid := mp.profileTimer
   624  		atomic.Store(&mp.profileTimerValid, 0)
   625  		mp.profileTimer = 0
   626  
   627  		ret := timer_delete(timerid)
   628  		if ret != 0 {
   629  			print("runtime: failed to disable profiling timer; timer_delete(", timerid, ") errno=", -ret, "\n")
   630  			throw("timer_delete")
   631  		}
   632  	}
   633  
   634  	if hz == 0 {
   635  		// If the goal was to disable profiling for this thread, then the job's done.
   636  		return
   637  	}
   638  
   639  	// The period of the timer should be 1/Hz. For every "1/Hz" of additional
   640  	// work, the user should expect one additional sample in the profile.
   641  	//
   642  	// But to scale down to very small amounts of application work, to observe
   643  	// even CPU usage of "one tenth" of the requested period, set the initial
   644  	// timing delay in a different way: So that "one tenth" of a period of CPU
   645  	// spend shows up as a 10% chance of one sample (for an expected value of
   646  	// 0.1 samples), and so that "two and six tenths" periods of CPU spend show
   647  	// up as a 60% chance of 3 samples and a 40% chance of 2 samples (for an
   648  	// expected value of 2.6). Set the initial delay to a value in the unifom
   649  	// random distribution between 0 and the desired period. And because "0"
   650  	// means "disable timer", add 1 so the half-open interval [0,period) turns
   651  	// into (0,period].
   652  	//
   653  	// Otherwise, this would show up as a bias away from short-lived threads and
   654  	// from threads that are only occasionally active: for example, when the
   655  	// garbage collector runs on a mostly-idle system, the additional threads it
   656  	// activates may do a couple milliseconds of GC-related work and nothing
   657  	// else in the few seconds that the profiler observes.
   658  	spec := new(itimerspec)
   659  	spec.it_value.setNsec(1 + int64(fastrandn(uint32(1e9/hz))))
   660  	spec.it_interval.setNsec(1e9 / int64(hz))
   661  
   662  	var timerid int32
   663  	var sevp sigevent
   664  	sevp.notify = _SIGEV_THREAD_ID
   665  	sevp.signo = _SIGPROF
   666  	sevp.sigev_notify_thread_id = int32(mp.procid)
   667  	ret := timer_create(_CLOCK_THREAD_CPUTIME_ID, &sevp, &timerid)
   668  	if ret != 0 {
   669  		// If we cannot create a timer for this M, leave profileTimerValid false
   670  		// to fall back to the process-wide setitimer profiler.
   671  		return
   672  	}
   673  
   674  	ret = timer_settime(timerid, 0, spec, nil)
   675  	if ret != 0 {
   676  		print("runtime: failed to configure profiling timer; timer_settime(", timerid,
   677  			", 0, {interval: {",
   678  			spec.it_interval.tv_sec, "s + ", spec.it_interval.tv_nsec, "ns} value: {",
   679  			spec.it_value.tv_sec, "s + ", spec.it_value.tv_nsec, "ns}}, nil) errno=", -ret, "\n")
   680  		throw("timer_settime")
   681  	}
   682  
   683  	mp.profileTimer = timerid
   684  	atomic.Store(&mp.profileTimerValid, 1)
   685  }
   686  
   687  // perThreadSyscallArgs contains the system call number, arguments, and
   688  // expected return values for a system call to be executed on all threads.
   689  type perThreadSyscallArgs struct {
   690  	trap uintptr
   691  	a1   uintptr
   692  	a2   uintptr
   693  	a3   uintptr
   694  	a4   uintptr
   695  	a5   uintptr
   696  	a6   uintptr
   697  	r1   uintptr
   698  	r2   uintptr
   699  }
   700  
   701  // perThreadSyscall is the system call to execute for the ongoing
   702  // doAllThreadsSyscall.
   703  //
   704  // perThreadSyscall may only be written while mp.needPerThreadSyscall == 0 on
   705  // all Ms.
   706  var perThreadSyscall perThreadSyscallArgs
   707  
   708  // syscall_runtime_doAllThreadsSyscall and executes a specified system call on
   709  // all Ms.
   710  //
   711  // The system call is expected to succeed and return the same value on every
   712  // thread. If any threads do not match, the runtime throws.
   713  //
   714  //go:linkname syscall_runtime_doAllThreadsSyscall syscall.runtime_doAllThreadsSyscall
   715  //go:uintptrescapes
   716  func syscall_runtime_doAllThreadsSyscall(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr) {
   717  	if iscgo {
   718  		// In cgo, we are not aware of threads created in C, so this approach will not work.
   719  		panic("doAllThreadsSyscall not supported with cgo enabled")
   720  	}
   721  
   722  	// STW to guarantee that user goroutines see an atomic change to thread
   723  	// state. Without STW, goroutines could migrate Ms while change is in
   724  	// progress and e.g., see state old -> new -> old -> new.
   725  	//
   726  	// N.B. Internally, this function does not depend on STW to
   727  	// successfully change every thread. It is only needed for user
   728  	// expectations, per above.
   729  	stopTheWorld("doAllThreadsSyscall")
   730  
   731  	// This function depends on several properties:
   732  	//
   733  	// 1. All OS threads that already exist are associated with an M in
   734  	//    allm. i.e., we won't miss any pre-existing threads.
   735  	// 2. All Ms listed in allm will eventually have an OS thread exist.
   736  	//    i.e., they will set procid and be able to receive signals.
   737  	// 3. OS threads created after we read allm will clone from a thread
   738  	//    that has executed the system call. i.e., they inherit the
   739  	//    modified state.
   740  	//
   741  	// We achieve these through different mechanisms:
   742  	//
   743  	// 1. Addition of new Ms to allm in allocm happens before clone of its
   744  	//    OS thread later in newm.
   745  	// 2. newm does acquirem to avoid being preempted, ensuring that new Ms
   746  	//    created in allocm will eventually reach OS thread clone later in
   747  	//    newm.
   748  	// 3. We take allocmLock for write here to prevent allocation of new Ms
   749  	//    while this function runs. Per (1), this prevents clone of OS
   750  	//    threads that are not yet in allm.
   751  	allocmLock.lock()
   752  
   753  	// Disable preemption, preventing us from changing Ms, as we handle
   754  	// this M specially.
   755  	//
   756  	// N.B. STW and lock() above do this as well, this is added for extra
   757  	// clarity.
   758  	acquirem()
   759  
   760  	// N.B. allocmLock also prevents concurrent execution of this function,
   761  	// serializing use of perThreadSyscall, mp.needPerThreadSyscall, and
   762  	// ensuring all threads execute system calls from multiple calls in the
   763  	// same order.
   764  
   765  	r1, r2, errno := syscall.Syscall6(trap, a1, a2, a3, a4, a5, a6)
   766  	if GOARCH == "ppc64" || GOARCH == "ppc64le" {
   767  		// TODO(https://go.dev/issue/51192 ): ppc64 doesn't use r2.
   768  		r2 = 0
   769  	}
   770  	if errno != 0 {
   771  		releasem(getg().m)
   772  		allocmLock.unlock()
   773  		startTheWorld()
   774  		return r1, r2, errno
   775  	}
   776  
   777  	perThreadSyscall = perThreadSyscallArgs{
   778  		trap: trap,
   779  		a1:   a1,
   780  		a2:   a2,
   781  		a3:   a3,
   782  		a4:   a4,
   783  		a5:   a5,
   784  		a6:   a6,
   785  		r1:   r1,
   786  		r2:   r2,
   787  	}
   788  
   789  	// Wait for all threads to start.
   790  	//
   791  	// As described above, some Ms have been added to allm prior to
   792  	// allocmLock, but not yet completed OS clone and set procid.
   793  	//
   794  	// At minimum we must wait for a thread to set procid before we can
   795  	// send it a signal.
   796  	//
   797  	// We take this one step further and wait for all threads to start
   798  	// before sending any signals. This prevents system calls from getting
   799  	// applied twice: once in the parent and once in the child, like so:
   800  	//
   801  	//          A                     B                  C
   802  	//                         add C to allm
   803  	// doAllThreadsSyscall
   804  	//   allocmLock.lock()
   805  	//   signal B
   806  	//                         <receive signal>
   807  	//                         execute syscall
   808  	//                         <signal return>
   809  	//                         clone C
   810  	//                                             <thread start>
   811  	//                                             set procid
   812  	//   signal C
   813  	//                                             <receive signal>
   814  	//                                             execute syscall
   815  	//                                             <signal return>
   816  	//
   817  	// In this case, thread C inherited the syscall-modified state from
   818  	// thread B and did not need to execute the syscall, but did anyway
   819  	// because doAllThreadsSyscall could not be sure whether it was
   820  	// required.
   821  	//
   822  	// Some system calls may not be idempotent, so we ensure each thread
   823  	// executes the system call exactly once.
   824  	for mp := allm; mp != nil; mp = mp.alllink {
   825  		for atomic.Load64(&mp.procid) == 0 {
   826  			// Thread is starting.
   827  			osyield()
   828  		}
   829  	}
   830  
   831  	// Signal every other thread, where they will execute perThreadSyscall
   832  	// from the signal handler.
   833  	gp := getg()
   834  	tid := gp.m.procid
   835  	for mp := allm; mp != nil; mp = mp.alllink {
   836  		if atomic.Load64(&mp.procid) == tid {
   837  			// Our thread already performed the syscall.
   838  			continue
   839  		}
   840  		mp.needPerThreadSyscall.Store(1)
   841  		signalM(mp, sigPerThreadSyscall)
   842  	}
   843  
   844  	// Wait for all threads to complete.
   845  	for mp := allm; mp != nil; mp = mp.alllink {
   846  		if mp.procid == tid {
   847  			continue
   848  		}
   849  		for mp.needPerThreadSyscall.Load() != 0 {
   850  			osyield()
   851  		}
   852  	}
   853  
   854  	perThreadSyscall = perThreadSyscallArgs{}
   855  
   856  	releasem(getg().m)
   857  	allocmLock.unlock()
   858  	startTheWorld()
   859  
   860  	return r1, r2, errno
   861  }
   862  
   863  // runPerThreadSyscall runs perThreadSyscall for this M if required.
   864  //
   865  // This function throws if the system call returns with anything other than the
   866  // expected values.
   867  //
   868  //go:nosplit
   869  func runPerThreadSyscall() {
   870  	gp := getg()
   871  	if gp.m.needPerThreadSyscall.Load() == 0 {
   872  		return
   873  	}
   874  
   875  	args := perThreadSyscall
   876  	r1, r2, errno := syscall.Syscall6(args.trap, args.a1, args.a2, args.a3, args.a4, args.a5, args.a6)
   877  	if GOARCH == "ppc64" || GOARCH == "ppc64le" {
   878  		// TODO(https://go.dev/issue/51192 ): ppc64 doesn't use r2.
   879  		r2 = 0
   880  	}
   881  	if errno != 0 || r1 != args.r1 || r2 != args.r2 {
   882  		print("trap:", args.trap, ", a123456=[", args.a1, ",", args.a2, ",", args.a3, ",", args.a4, ",", args.a5, ",", args.a6, "]\n")
   883  		print("results: got {r1=", r1, ",r2=", r2, ",errno=", errno, "}, want {r1=", args.r1, ",r2=", args.r2, ",errno=0\n")
   884  		fatal("AllThreadsSyscall6 results differ between threads; runtime corrupted")
   885  	}
   886  
   887  	gp.m.needPerThreadSyscall.Store(0)
   888  }
   889  

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