ggstd/runtime/

os_linux.rs

// Copyright 2023 The rust-ggstd authors. All rights reserved.
// 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.

use std::io::Read;

// import (
// 	"internal/abi"
// 	"internal/goarch"
// 	"runtime/internal/atomic"
// 	"runtime/internal/syscall"
// 	"unsafe"
// )

// // sigPerThreadSyscall is the same signal (SIGSETXID) used by glibc for
// // per-thread syscalls on Linux. We use it for the same purpose in non-cgo
// // binaries.
// const sigPerThreadSyscall = _SIGRTMIN + 1

// type mOS struct {
// 	// profileTimer holds the ID of the POSIX interval timer for profiling CPU
// 	// usage on this thread.
// 	//
// 	// It is valid when the profileTimerValid field is true. A thread
// 	// creates and manages its own timer, and these fields are read and written
// 	// only by this thread. But because some of the reads on profileTimerValid
// 	// are in signal handling code, this field should be atomic type.
// 	profileTimer      int32
// 	profileTimerValid atomic.Bool

// 	// needPerThreadSyscall indicates that a per-thread syscall is required
// 	// for doAllThreadsSyscall.
// 	needPerThreadSyscall atomic.Uint8
// }

// //go:noescape
// func futex(addr unsafe.Pointer, op int32, val uint32, ts, addr2 unsafe.Pointer, val3 uint32) int32

// // Linux futex.
// //
// //	futexsleep(uint32 *addr, uint32 val)
// //	futexwakeup(uint32 *addr)
// //
// // Futexsleep atomically checks if *addr == val and if so, sleeps on addr.
// // Futexwakeup wakes up threads sleeping on addr.
// // Futexsleep is allowed to wake up spuriously.

// const (
// 	_FUTEX_PRIVATE_FLAG = 128
// 	_FUTEX_WAIT_PRIVATE = 0 | _FUTEX_PRIVATE_FLAG
// 	_FUTEX_WAKE_PRIVATE = 1 | _FUTEX_PRIVATE_FLAG
// )

// // Atomically,
// //
// //	if(*addr == val) sleep
// //
// // Might be woken up spuriously; that's allowed.
// // Don't sleep longer than ns; ns < 0 means forever.
// //
// //go:nosplit
// func futexsleep(addr *uint32, val uint32, ns int64) {
// 	// Some Linux kernels have a bug where futex of
// 	// FUTEX_WAIT returns an internal error code
// 	// as an errno. Libpthread ignores the return value
// 	// here, and so can we: as it says a few lines up,
// 	// spurious wakeups are allowed.
// 	if ns < 0 {
// 		futex(unsafe.Pointer(addr), _FUTEX_WAIT_PRIVATE, val, nil, nil, 0)
// 		return
// 	}

// 	var ts timespec
// 	ts.setNsec(ns)
// 	futex(unsafe.Pointer(addr), _FUTEX_WAIT_PRIVATE, val, unsafe.Pointer(&ts), nil, 0)
// }

// // If any procs are sleeping on addr, wake up at most cnt.
// //
// //go:nosplit
// func futexwakeup(addr *uint32, cnt uint32) {
// 	ret := futex(unsafe.Pointer(addr), _FUTEX_WAKE_PRIVATE, cnt, nil, nil, 0)
// 	if ret >= 0 {
// 		return
// 	}

// 	// I don't know that futex wakeup can return
// 	// EAGAIN or EINTR, but if it does, it would be
// 	// safe to loop and call futex again.
// 	systemstack(func() {
// 		print("futexwakeup addr=", addr, " returned ", ret, "\n")
// 	})

// 	*(*int32)(unsafe.Pointer(uintptr(0x1006))) = 0x1006
// }

// func getproccount() int32 {
// 	// This buffer is huge (8 kB) but we are on the system stack
// 	// and there should be plenty of space (64 kB).
// 	// Also this is a leaf, so we're not holding up the memory for long.
// 	// See golang.org/issue/11823.
// 	// The suggested behavior here is to keep trying with ever-larger
// 	// buffers, but we don't have a dynamic memory allocator at the
// 	// moment, so that's a bit tricky and seems like overkill.
// 	const maxCPUs = 64 * 1024
// 	var buf [maxCPUs / 8]byte
// 	r := sched_getaffinity(0, unsafe.Sizeof(buf), &buf[0])
// 	if r < 0 {
// 		return 1
// 	}
// 	n := int32(0)
// 	for _, v := range buf[:r] {
// 		for v != 0 {
// 			n += int32(v & 1)
// 			v >>= 1
// 		}
// 	}
// 	if n == 0 {
// 		n = 1
// 	}
// 	return n
// }

// // Clone, the Linux rfork.
// const (
// 	_CLONE_VM             = 0x100
// 	_CLONE_FS             = 0x200
// 	_CLONE_FILES          = 0x400
// 	_CLONE_SIGHAND        = 0x800
// 	_CLONE_PTRACE         = 0x2000
// 	_CLONE_VFORK          = 0x4000
// 	_CLONE_PARENT         = 0x8000
// 	_CLONE_THREAD         = 0x10000
// 	_CLONE_NEWNS          = 0x20000
// 	_CLONE_SYSVSEM        = 0x40000
// 	_CLONE_SETTLS         = 0x80000
// 	_CLONE_PARENT_SETTID  = 0x100000
// 	_CLONE_CHILD_CLEARTID = 0x200000
// 	_CLONE_UNTRACED       = 0x800000
// 	_CLONE_CHILD_SETTID   = 0x1000000
// 	_CLONE_STOPPED        = 0x2000000
// 	_CLONE_NEWUTS         = 0x4000000
// 	_CLONE_NEWIPC         = 0x8000000

// 	// As of QEMU 2.8.0 (5ea2fc84d), user emulation requires all six of these
// 	// flags to be set when creating a thread; attempts to share the other
// 	// five but leave SYSVSEM unshared will fail with -EINVAL.
// 	//
// 	// In non-QEMU environments CLONE_SYSVSEM is inconsequential as we do not
// 	// use System V semaphores.

// 	cloneFlags = _CLONE_VM | /* share memory */
// 		_CLONE_FS | /* share cwd, etc */
// 		_CLONE_FILES | /* share fd table */
// 		_CLONE_SIGHAND | /* share sig handler table */
// 		_CLONE_SYSVSEM | /* share SysV semaphore undo lists (see issue #20763) */
// 		_CLONE_THREAD /* revisit - okay for now */
// )

// //go:noescape
// func clone(flags int32, stk, mp, gp, fn unsafe.Pointer) int32

// // May run with m.p==nil, so write barriers are not allowed.
// //
// //go:nowritebarrier
// func newosproc(mp *m) {
// 	stk := unsafe.Pointer(mp.g0.stack.hi)
// 	/*
// 	 * note: strace gets confused if we use CLONE_PTRACE here.
// 	 */
// 	if false {
// 		print("newosproc stk=", stk, " m=", mp, " g=", mp.g0, " clone=", abi.FuncPCABI0(clone), " id=", mp.id, " ostk=", &mp, "\n")
// 	}

// 	// Disable signals during clone, so that the new thread starts
// 	// with signals disabled. It will enable them in minit.
// 	var oset sigset
// 	sigprocmask(_SIG_SETMASK, &sigset_all, &oset)
// 	ret := retryOnEAGAIN(func() int32 {
// 		r := clone(cloneFlags, stk, unsafe.Pointer(mp), unsafe.Pointer(mp.g0), unsafe.Pointer(abi.FuncPCABI0(mstart)))
// 		// clone returns positive TID, negative errno.
// 		// We don't care about the TID.
// 		if r >= 0 {
// 			return 0
// 		}
// 		return -r
// 	})
// 	sigprocmask(_SIG_SETMASK, &oset, nil)

// 	if ret != 0 {
// 		print("runtime: failed to create new OS thread (have ", mcount(), " already; errno=", ret, ")\n")
// 		if ret == _EAGAIN {
// 			println("runtime: may need to increase max user processes (ulimit -u)")
// 		}
// 		throw("newosproc")
// 	}
// }

// // Version of newosproc that doesn't require a valid G.
// //
// //go:nosplit
// func newosproc0(stacksize uintptr, fn unsafe.Pointer) {
// 	stack := sysAlloc(stacksize, &memstats.stacks_sys)
// 	if stack == nil {
// 		writeErrStr(failallocatestack)
// 		exit(1)
// 	}
// 	ret := clone(cloneFlags, unsafe.Pointer(uintptr(stack)+stacksize), nil, nil, fn)
// 	if ret < 0 {
// 		writeErrStr(failthreadcreate)
// 		exit(1)
// 	}
// }

// const (
// 	_AT_NULL   = 0  // End of vector
// 	_AT_PAGESZ = 6  // System physical page size
// 	_AT_HWCAP  = 16 // hardware capability bit vector
// 	_AT_SECURE = 23 // secure mode boolean
// 	_AT_RANDOM = 25 // introduced in 2.6.29
// 	_AT_HWCAP2 = 26 // hardware capability bit vector 2
// )

// var procAuxv = []byte("/proc/self/auxv\x00")

// var addrspace_vec [1]byte

// func mincore(addr unsafe.Pointer, n uintptr, dst *byte) int32

// func sysargs(argc int32, argv **byte) {
// 	n := argc + 1

// 	// skip over argv, envp to get to auxv
// 	for argv_index(argv, n) != nil {
// 		n++
// 	}

// 	// skip NULL separator
// 	n++

// 	// now argv+n is auxv
// 	auxv := (*[1 << 28]uintptr)(add(unsafe.Pointer(argv), uintptr(n)*goarch.PtrSize))
// 	if sysauxv(auxv[:]) != 0 {
// 		return
// 	}
// 	// In some situations we don't get a loader-provided
// 	// auxv, such as when loaded as a library on Android.
// 	// Fall back to /proc/self/auxv.
// 	fd := open(&procAuxv[0], 0 /* O_RDONLY */, 0)
// 	if fd < 0 {
// 		// On Android, /proc/self/auxv might be unreadable (issue 9229), so we fallback to
// 		// try using mincore to detect the physical page size.
// 		// mincore should return EINVAL when address is not a multiple of system page size.
// 		const size = 256 << 10 // size of memory region to allocate
// 		p, err := mmap(nil, size, _PROT_READ|_PROT_WRITE, _MAP_ANON|_MAP_PRIVATE, -1, 0)
// 		if err != 0 {
// 			return
// 		}
// 		var n uintptr
// 		for n = 4 << 10; n < size; n <<= 1 {
// 			err := mincore(unsafe.Pointer(uintptr(p)+n), 1, &addrspace_vec[0])
// 			if err == 0 {
// 				physPageSize = n
// 				break
// 			}
// 		}
// 		if physPageSize == 0 {
// 			physPageSize = size
// 		}
// 		munmap(p, size)
// 		return
// 	}
// 	var buf [128]uintptr
// 	n = read(fd, noescape(unsafe.Pointer(&buf[0])), int32(unsafe.Sizeof(buf)))
// 	closefd(fd)
// 	if n < 0 {
// 		return
// 	}
// 	// Make sure buf is terminated, even if we didn't read
// 	// the whole file.
// 	buf[len(buf)-2] = _AT_NULL
// 	sysauxv(buf[:])
// }

// // startupRandomData holds random bytes initialized at startup. These come from
// // the ELF AT_RANDOM auxiliary vector.
// var startupRandomData []byte

// // secureMode holds the value of AT_SECURE passed in the auxiliary vector.
// var secureMode bool

// func sysauxv(auxv []uintptr) int {
// 	var i int
// 	for ; auxv[i] != _AT_NULL; i += 2 {
// 		tag, val := auxv[i], auxv[i+1]
// 		switch tag {
// 		case _AT_RANDOM:
// 			// The kernel provides a pointer to 16-bytes
// 			// worth of random data.
// 			startupRandomData = (*[16]byte)(unsafe.Pointer(val))[:]

// 		case _AT_PAGESZ:
// 			physPageSize = val

// 		case _AT_SECURE:
// 			secureMode = val == 1
// 		}

// 		archauxv(tag, val)
// 		vdsoauxv(tag, val)
// 	}
// 	return i / 2
// }

// var sysTHPSizePath = []byte("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size\x00")

// func getHugePageSize() uintptr {
// 	var numbuf [20]byte
// 	fd := open(&sysTHPSizePath[0], 0 /* O_RDONLY */, 0)
// 	if fd < 0 {
// 		return 0
// 	}
// 	ptr := noescape(unsafe.Pointer(&numbuf[0]))
// 	n := read(fd, ptr, int32(len(numbuf)))
// 	closefd(fd)
// 	if n <= 0 {
// 		return 0
// 	}
// 	n-- // remove trailing newline
// 	v, ok := atoi(slicebytetostringtmp((*byte)(ptr), int(n)))
// 	if !ok || v < 0 {
// 		v = 0
// 	}
// 	if v&(v-1) != 0 {
// 		// v is not a power of 2
// 		return 0
// 	}
// 	return uintptr(v)
// }

// func osinit() {
// 	ncpu = getproccount()
// 	physHugePageSize = getHugePageSize()
// 	if iscgo {
// 		// #42494 glibc and musl reserve some signals for
// 		// internal use and require they not be blocked by
// 		// the rest of a normal C runtime. When the go runtime
// 		// blocks...unblocks signals, temporarily, the blocked
// 		// interval of time is generally very short. As such,
// 		// these expectations of *libc code are mostly met by
// 		// the combined go+cgo system of threads. However,
// 		// when go causes a thread to exit, via a return from
// 		// mstart(), the combined runtime can deadlock if
// 		// these signals are blocked. Thus, don't block these
// 		// signals when exiting threads.
// 		// - glibc: SIGCANCEL (32), SIGSETXID (33)
// 		// - musl: SIGTIMER (32), SIGCANCEL (33), SIGSYNCCALL (34)
// 		sigdelset(&sigsetAllExiting, 32)
// 		sigdelset(&sigsetAllExiting, 33)
// 		sigdelset(&sigsetAllExiting, 34)
// 	}
// 	osArchInit()
// }

// var urandom_dev = []byte("/dev/urandom\x00")

pub fn get_random_data(r: &mut [u8]) {
    // 	if startupRandomData != nil {
    // 		n := copy(r, startupRandomData)
    // 		extendRandom(r, n)
    // 		return
    // 	}
    match &mut std::fs::File::open("/dev/urandom") {
        Err(err) => panic!("failed to open /dev/urandom: {}", err),
        Ok(f) => {
            if let Err(err) = f.read_exact(r) {
                panic!("failed to open /dev/urandom: {}", err);
            }
        }
    }
    // 	fd := open(&urandom_dev[0], 0 /* O_RDONLY */, 0)
    // 	n := read(fd, unsafe.Pointer(&r[0]), int32(len(r)))
    // 	closefd(fd)
    // 	extendRandom(r, int(n))
}

// func goenvs() {
// 	goenvs_unix()
// }

// // Called to do synchronous initialization of Go code built with
// // -buildmode=c-archive or -buildmode=c-shared.
// // None of the Go runtime is initialized.
// //
// //go:nosplit
// //go:nowritebarrierrec
// func libpreinit() {
// 	initsig(true)
// }

// // Called to initialize a new m (including the bootstrap m).
// // Called on the parent thread (main thread in case of bootstrap), can allocate memory.
// func mpreinit(mp *m) {
// 	mp.gsignal = malg(32 * 1024) // Linux wants >= 2K
// 	mp.gsignal.m = mp
// }

// func gettid() uint32

// // Called to initialize a new m (including the bootstrap m).
// // Called on the new thread, cannot allocate memory.
// func minit() {
// 	minitSignals()

// 	// Cgo-created threads and the bootstrap m are missing a
// 	// procid. We need this for asynchronous preemption and it's
// 	// useful in debuggers.
// 	getg().m.procid = uint64(gettid())
// }

// // Called from dropm to undo the effect of an minit.
// //
// //go:nosplit
// func unminit() {
// 	unminitSignals()
// }

// // Called from exitm, but not from drop, to undo the effect of thread-owned
// // resources in minit, semacreate, or elsewhere. Do not take locks after calling this.
// func mdestroy(mp *m) {
// }

// //#ifdef GOARCH_386
// //#define sa_handler k_sa_handler
// //#endif

// func sigreturn()
// func sigtramp() // Called via C ABI
// func cgoSigtramp()

// //go:noescape
// func sigaltstack(new, old *stackt)

// //go:noescape
// func setitimer(mode int32, new, old *itimerval)

// //go:noescape
// func timer_create(clockid int32, sevp *sigevent, timerid *int32) int32

// //go:noescape
// func timer_settime(timerid int32, flags int32, new, old *itimerspec) int32

// //go:noescape
// func timer_delete(timerid int32) int32

// //go:noescape
// func rtsigprocmask(how int32, new, old *sigset, size int32)

// //go:nosplit
// //go:nowritebarrierrec
// func sigprocmask(how int32, new, old *sigset) {
// 	rtsigprocmask(how, new, old, int32(unsafe.Sizeof(*new)))
// }

// func raise(sig uint32)
// func raiseproc(sig uint32)

// //go:noescape
// func sched_getaffinity(pid, len uintptr, buf *byte) int32
// func osyield()

// //go:nosplit
// func osyield_no_g() {
// 	osyield()
// }

// func pipe2(flags int32) (r, w int32, errno int32)

// //go:nosplit
// func fcntl(fd, cmd, arg int32) (ret int32, errno int32) {
// 	r, _, err := syscall.Syscall6(syscall.SYS_FCNTL, uintptr(fd), uintptr(cmd), uintptr(arg), 0, 0, 0)
// 	return int32(r), int32(err)
// }

// const (
// 	_si_max_size    = 128
// 	_sigev_max_size = 64
// )

// //go:nosplit
// //go:nowritebarrierrec
// func setsig(i uint32, fn uintptr) {
// 	var sa sigactiont
// 	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK | _SA_RESTORER | _SA_RESTART
// 	sigfillset(&sa.sa_mask)
// 	// Although Linux manpage says "sa_restorer element is obsolete and
// 	// should not be used". x86_64 kernel requires it. Only use it on
// 	// x86.
// 	if GOARCH == "386" || GOARCH == "amd64" {
// 		sa.sa_restorer = abi.FuncPCABI0(sigreturn)
// 	}
// 	if fn == abi.FuncPCABIInternal(sighandler) { // abi.FuncPCABIInternal(sighandler) matches the callers in signal_unix.go
// 		if iscgo {
// 			fn = abi.FuncPCABI0(cgoSigtramp)
// 		} else {
// 			fn = abi.FuncPCABI0(sigtramp)
// 		}
// 	}
// 	sa.sa_handler = fn
// 	sigaction(i, &sa, nil)
// }

// //go:nosplit
// //go:nowritebarrierrec
// func setsigstack(i uint32) {
// 	var sa sigactiont
// 	sigaction(i, nil, &sa)
// 	if sa.sa_flags&_SA_ONSTACK != 0 {
// 		return
// 	}
// 	sa.sa_flags |= _SA_ONSTACK
// 	sigaction(i, &sa, nil)
// }

// //go:nosplit
// //go:nowritebarrierrec
// func getsig(i uint32) uintptr {
// 	var sa sigactiont
// 	sigaction(i, nil, &sa)
// 	return sa.sa_handler
// }

// // setSignalstackSP sets the ss_sp field of a stackt.
// //
// //go:nosplit
// func setSignalstackSP(s *stackt, sp uintptr) {
// 	*(*uintptr)(unsafe.Pointer(&s.ss_sp)) = sp
// }

// //go:nosplit
// func (c *sigctxt) fixsigcode(sig uint32) {
// }

// // sysSigaction calls the rt_sigaction system call.
// //
// //go:nosplit
// func sysSigaction(sig uint32, new, old *sigactiont) {
// 	if rt_sigaction(uintptr(sig), new, old, unsafe.Sizeof(sigactiont{}.sa_mask)) != 0 {
// 		// Workaround for bugs in QEMU user mode emulation.
// 		//
// 		// QEMU turns calls to the sigaction system call into
// 		// calls to the C library sigaction call; the C
// 		// library call rejects attempts to call sigaction for
// 		// SIGCANCEL (32) or SIGSETXID (33).
// 		//
// 		// QEMU rejects calling sigaction on SIGRTMAX (64).
// 		//
// 		// Just ignore the error in these case. There isn't
// 		// anything we can do about it anyhow.
// 		if sig != 32 && sig != 33 && sig != 64 {
// 			// Use system stack to avoid split stack overflow on ppc64/ppc64le.
// 			systemstack(func() {
// 				throw("sigaction failed")
// 			})
// 		}
// 	}
// }

// // rt_sigaction is implemented in assembly.
// //
// //go:noescape
// func rt_sigaction(sig uintptr, new, old *sigactiont, size uintptr) int32

// func getpid() int
// func tgkill(tgid, tid, sig int)

// // signalM sends a signal to mp.
// func signalM(mp *m, sig int) {
// 	tgkill(getpid(), int(mp.procid), sig)
// }

// // go118UseTimerCreateProfiler enables the per-thread CPU profiler.
// const go118UseTimerCreateProfiler = true

// // validSIGPROF compares this signal delivery's code against the signal sources
// // that the profiler uses, returning whether the delivery should be processed.
// // To be processed, a signal delivery from a known profiling mechanism should
// // correspond to the best profiling mechanism available to this thread. Signals
// // from other sources are always considered valid.
// //
// //go:nosplit
// func validSIGPROF(mp *m, c *sigctxt) bool {
// 	code := int32(c.sigcode())
// 	setitimer := code == _SI_KERNEL
// 	timer_create := code == _SI_TIMER

// 	if !(setitimer || timer_create) {
// 		// The signal doesn't correspond to a profiling mechanism that the
// 		// runtime enables itself. There's no reason to process it, but there's
// 		// no reason to ignore it either.
// 		return true
// 	}

// 	if mp == nil {
// 		// Since we don't have an M, we can't check if there's an active
// 		// per-thread timer for this thread. We don't know how long this thread
// 		// has been around, and if it happened to interact with the Go scheduler
// 		// at a time when profiling was active (causing it to have a per-thread
// 		// timer). But it may have never interacted with the Go scheduler, or
// 		// never while profiling was active. To avoid double-counting, process
// 		// only signals from setitimer.
// 		//
// 		// When a custom cgo traceback function has been registered (on
// 		// platforms that support runtime.SetCgoTraceback), SIGPROF signals
// 		// delivered to a thread that cannot find a matching M do this check in
// 		// the assembly implementations of runtime.cgoSigtramp.
// 		return setitimer
// 	}

// 	// Having an M means the thread interacts with the Go scheduler, and we can
// 	// check whether there's an active per-thread timer for this thread.
// 	if mp.profileTimerValid.Load() {
// 		// If this M has its own per-thread CPU profiling interval timer, we
// 		// should track the SIGPROF signals that come from that timer (for
// 		// accurate reporting of its CPU usage; see issue 35057) and ignore any
// 		// that it gets from the process-wide setitimer (to not over-count its
// 		// CPU consumption).
// 		return timer_create
// 	}

// 	// No active per-thread timer means the only valid profiler is setitimer.
// 	return setitimer
// }

// func setProcessCPUProfiler(hz int32) {
// 	setProcessCPUProfilerTimer(hz)
// }

// func setThreadCPUProfiler(hz int32) {
// 	mp := getg().m
// 	mp.profilehz = hz

// 	if !go118UseTimerCreateProfiler {
// 		return
// 	}

// 	// destroy any active timer
// 	if mp.profileTimerValid.Load() {
// 		timerid := mp.profileTimer
// 		mp.profileTimerValid.Store(false)
// 		mp.profileTimer = 0

// 		ret := timer_delete(timerid)
// 		if ret != 0 {
// 			print("runtime: failed to disable profiling timer; timer_delete(", timerid, ") errno=", -ret, "\n")
// 			throw("timer_delete")
// 		}
// 	}

// 	if hz == 0 {
// 		// If the goal was to disable profiling for this thread, then the job's done.
// 		return
// 	}

// 	// The period of the timer should be 1/Hz. For every "1/Hz" of additional
// 	// work, the user should expect one additional sample in the profile.
// 	//
// 	// But to scale down to very small amounts of application work, to observe
// 	// even CPU usage of "one tenth" of the requested period, set the initial
// 	// timing delay in a different way: So that "one tenth" of a period of CPU
// 	// spend shows up as a 10% chance of one sample (for an expected value of
// 	// 0.1 samples), and so that "two and six tenths" periods of CPU spend show
// 	// up as a 60% chance of 3 samples and a 40% chance of 2 samples (for an
// 	// expected value of 2.6). Set the initial delay to a value in the unifom
// 	// random distribution between 0 and the desired period. And because "0"
// 	// means "disable timer", add 1 so the half-open interval [0,period) turns
// 	// into (0,period].
// 	//
// 	// Otherwise, this would show up as a bias away from short-lived threads and
// 	// from threads that are only occasionally active: for example, when the
// 	// garbage collector runs on a mostly-idle system, the additional threads it
// 	// activates may do a couple milliseconds of GC-related work and nothing
// 	// else in the few seconds that the profiler observes.
// 	spec := new(itimerspec)
// 	spec.it_value.setNsec(1 + int64(fastrandn(uint32(1e9/hz))))
// 	spec.it_interval.setNsec(1e9 / int64(hz))

// 	var timerid int32
// 	var sevp sigevent
// 	sevp.notify = _SIGEV_THREAD_ID
// 	sevp.signo = _SIGPROF
// 	sevp.sigev_notify_thread_id = int32(mp.procid)
// 	ret := timer_create(_CLOCK_THREAD_CPUTIME_ID, &sevp, &timerid)
// 	if ret != 0 {
// 		// If we cannot create a timer for this M, leave profileTimerValid false
// 		// to fall back to the process-wide setitimer profiler.
// 		return
// 	}

// 	ret = timer_settime(timerid, 0, spec, nil)
// 	if ret != 0 {
// 		print("runtime: failed to configure profiling timer; timer_settime(", timerid,
// 			", 0, {interval: {",
// 			spec.it_interval.tv_sec, "s + ", spec.it_interval.tv_nsec, "ns} value: {",
// 			spec.it_value.tv_sec, "s + ", spec.it_value.tv_nsec, "ns}}, nil) errno=", -ret, "\n")
// 		throw("timer_settime")
// 	}

// 	mp.profileTimer = timerid
// 	mp.profileTimerValid.Store(true)
// }

// // perThreadSyscallArgs contains the system call number, arguments, and
// // expected return values for a system call to be executed on all threads.
// type perThreadSyscallArgs struct {
// 	trap uintptr
// 	a1   uintptr
// 	a2   uintptr
// 	a3   uintptr
// 	a4   uintptr
// 	a5   uintptr
// 	a6   uintptr
// 	r1   uintptr
// 	r2   uintptr
// }

// // perThreadSyscall is the system call to execute for the ongoing
// // doAllThreadsSyscall.
// //
// // perThreadSyscall may only be written while mp.needPerThreadSyscall == 0 on
// // all Ms.
// var perThreadSyscall perThreadSyscallArgs

// // syscall_runtime_doAllThreadsSyscall and executes a specified system call on
// // all Ms.
// //
// // The system call is expected to succeed and return the same value on every
// // thread. If any threads do not match, the runtime throws.
// //
// //go:linkname syscall_runtime_doAllThreadsSyscall syscall.runtime_doAllThreadsSyscall
// //go:uintptrescapes
// func syscall_runtime_doAllThreadsSyscall(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr) {
// 	if iscgo {
// 		// In cgo, we are not aware of threads created in C, so this approach will not work.
// 		panic("doAllThreadsSyscall not supported with cgo enabled")
// 	}

// 	// STW to guarantee that user goroutines see an atomic change to thread
// 	// state. Without STW, goroutines could migrate Ms while change is in
// 	// progress and e.g., see state old -> new -> old -> new.
// 	//
// 	// N.B. Internally, this function does not depend on STW to
// 	// successfully change every thread. It is only needed for user
// 	// expectations, per above.
// 	stopTheWorld("doAllThreadsSyscall")

// 	// This function depends on several properties:
// 	//
// 	// 1. All OS threads that already exist are associated with an M in
// 	//    allm. i.e., we won't miss any pre-existing threads.
// 	// 2. All Ms listed in allm will eventually have an OS thread exist.
// 	//    i.e., they will set procid and be able to receive signals.
// 	// 3. OS threads created after we read allm will clone from a thread
// 	//    that has executed the system call. i.e., they inherit the
// 	//    modified state.
// 	//
// 	// We achieve these through different mechanisms:
// 	//
// 	// 1. Addition of new Ms to allm in allocm happens before clone of its
// 	//    OS thread later in newm.
// 	// 2. newm does acquirem to avoid being preempted, ensuring that new Ms
// 	//    created in allocm will eventually reach OS thread clone later in
// 	//    newm.
// 	// 3. We take allocmLock for write here to prevent allocation of new Ms
// 	//    while this function runs. Per (1), this prevents clone of OS
// 	//    threads that are not yet in allm.
// 	allocmLock.lock()

// 	// Disable preemption, preventing us from changing Ms, as we handle
// 	// this M specially.
// 	//
// 	// N.B. STW and lock() above do this as well, this is added for extra
// 	// clarity.
// 	acquirem()

// 	// N.B. allocmLock also prevents concurrent execution of this function,
// 	// serializing use of perThreadSyscall, mp.needPerThreadSyscall, and
// 	// ensuring all threads execute system calls from multiple calls in the
// 	// same order.

// 	r1, r2, errno := syscall.Syscall6(trap, a1, a2, a3, a4, a5, a6)
// 	if GOARCH == "ppc64" || GOARCH == "ppc64le" {
// 		// TODO(https://go.dev/issue/51192 ): ppc64 doesn't use r2.
// 		r2 = 0
// 	}
// 	if errno != 0 {
// 		releasem(getg().m)
// 		allocmLock.unlock()
// 		startTheWorld()
// 		return r1, r2, errno
// 	}

// 	perThreadSyscall = perThreadSyscallArgs{
// 		trap: trap,
// 		a1:   a1,
// 		a2:   a2,
// 		a3:   a3,
// 		a4:   a4,
// 		a5:   a5,
// 		a6:   a6,
// 		r1:   r1,
// 		r2:   r2,
// 	}

// 	// Wait for all threads to start.
// 	//
// 	// As described above, some Ms have been added to allm prior to
// 	// allocmLock, but not yet completed OS clone and set procid.
// 	//
// 	// At minimum we must wait for a thread to set procid before we can
// 	// send it a signal.
// 	//
// 	// We take this one step further and wait for all threads to start
// 	// before sending any signals. This prevents system calls from getting
// 	// applied twice: once in the parent and once in the child, like so:
// 	//
// 	//          A                     B                  C
// 	//                         add C to allm
// 	// doAllThreadsSyscall
// 	//   allocmLock.lock()
// 	//   signal B
// 	//                         <receive signal>
// 	//                         execute syscall
// 	//                         <signal return>
// 	//                         clone C
// 	//                                             <thread start>
// 	//                                             set procid
// 	//   signal C
// 	//                                             <receive signal>
// 	//                                             execute syscall
// 	//                                             <signal return>
// 	//
// 	// In this case, thread C inherited the syscall-modified state from
// 	// thread B and did not need to execute the syscall, but did anyway
// 	// because doAllThreadsSyscall could not be sure whether it was
// 	// required.
// 	//
// 	// Some system calls may not be idempotent, so we ensure each thread
// 	// executes the system call exactly once.
// 	for mp := allm; mp != nil; mp = mp.alllink {
// 		for atomic.Load64(&mp.procid) == 0 {
// 			// Thread is starting.
// 			osyield()
// 		}
// 	}

// 	// Signal every other thread, where they will execute perThreadSyscall
// 	// from the signal handler.
// 	gp := getg()
// 	tid := gp.m.procid
// 	for mp := allm; mp != nil; mp = mp.alllink {
// 		if atomic.Load64(&mp.procid) == tid {
// 			// Our thread already performed the syscall.
// 			continue
// 		}
// 		mp.needPerThreadSyscall.Store(1)
// 		signalM(mp, sigPerThreadSyscall)
// 	}

// 	// Wait for all threads to complete.
// 	for mp := allm; mp != nil; mp = mp.alllink {
// 		if mp.procid == tid {
// 			continue
// 		}
// 		for mp.needPerThreadSyscall.Load() != 0 {
// 			osyield()
// 		}
// 	}

// 	perThreadSyscall = perThreadSyscallArgs{}

// 	releasem(getg().m)
// 	allocmLock.unlock()
// 	startTheWorld()

// 	return r1, r2, errno
// }

// // runPerThreadSyscall runs perThreadSyscall for this M if required.
// //
// // This function throws if the system call returns with anything other than the
// // expected values.
// //
// //go:nosplit
// func runPerThreadSyscall() {
// 	gp := getg()
// 	if gp.m.needPerThreadSyscall.Load() == 0 {
// 		return
// 	}

// 	args := perThreadSyscall
// 	r1, r2, errno := syscall.Syscall6(args.trap, args.a1, args.a2, args.a3, args.a4, args.a5, args.a6)
// 	if GOARCH == "ppc64" || GOARCH == "ppc64le" {
// 		// TODO(https://go.dev/issue/51192 ): ppc64 doesn't use r2.
// 		r2 = 0
// 	}
// 	if errno != 0 || r1 != args.r1 || r2 != args.r2 {
// 		print("trap:", args.trap, ", a123456=[", args.a1, ",", args.a2, ",", args.a3, ",", args.a4, ",", args.a5, ",", args.a6, "]\n")
// 		print("results: got {r1=", r1, ",r2=", r2, ",errno=", errno, "}, want {r1=", args.r1, ",r2=", args.r2, ",errno=0}\n")
// 		fatal("AllThreadsSyscall6 results differ between threads; runtime corrupted")
// 	}

// 	gp.m.needPerThreadSyscall.Store(0)
// }

// const (
// 	_SI_USER  = 0
// 	_SI_TKILL = -6
// )

// // sigFromUser reports whether the signal was sent because of a call
// // to kill or tgkill.
// //
// //go:nosplit
// func (c *sigctxt) sigFromUser() bool {
// 	code := int32(c.sigcode())
// 	return code == _SI_USER || code == _SI_TKILL
// }