src/runtime/os_linux.go

// 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.

package runtime

import (
	"runtime/internal/sys"
	"unsafe"
)

type mOS struct{}

//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_WAIT = 0
	_FUTEX_WAKE = 1
)

// 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) {
	var ts timespec

	// 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, val, nil, nil, 0)
		return
	}

	// It's difficult to live within the no-split stack limits here.
	// On ARM and 386, a 64-bit divide invokes a general software routine
	// that needs more stack than we can afford. So we use timediv instead.
	// But on real 64-bit systems, where words are larger but the stack limit
	// is not, even timediv is too heavy, and we really need to use just an
	// ordinary machine instruction.
	if sys.PtrSize == 8 {
		ts.set_sec(ns / 1000000000)
		ts.set_nsec(int32(ns % 1000000000))
	} else {
		ts.tv_nsec = 0
		ts.set_sec(int64(timediv(ns, 1000000000, (*int32)(unsafe.Pointer(&ts.tv_nsec)))))
	}
	futex(unsafe.Pointer(addr), _FUTEX_WAIT, 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, 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 / (sys.PtrSize * 8)]uintptr
	r := sched_getaffinity(0, unsafe.Sizeof(buf), &buf[0])
	if r < 0 {
		return 1
	}
	n := int32(0)
	for _, v := range buf[:r/sys.PtrSize] {
		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

	cloneFlags = _CLONE_VM | /* share memory */
		_CLONE_FS | /* share cwd, etc */
		_CLONE_FILES | /* share fd table */
		_CLONE_SIGHAND | /* share sig handler table */
		_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) {
	/*
	 * note: strace gets confused if we use CLONE_PTRACE here.
	 */
	if false {
		print("newosproc stk=", stk, " m=", mp, " g=", mp.g0, " clone=", funcPC(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 := clone(cloneFlags, stk, unsafe.Pointer(mp), unsafe.Pointer(mp.g0), unsafe.Pointer(funcPC(mstart)))
	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 {
		write(2, unsafe.Pointer(&failallocatestack[0]), int32(len(failallocatestack)))
		exit(1)
	}
	ret := clone(cloneFlags, unsafe.Pointer(uintptr(stack)+stacksize), nil, nil, fn)
	if ret < 0 {
		write(2, unsafe.Pointer(&failthreadcreate[0]), int32(len(failthreadcreate)))
		exit(1)
	}
}

var failallocatestack = []byte("runtime: failed to allocate stack for the new OS thread\n")
var failthreadcreate = []byte("runtime: failed to create new OS thread\n")

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

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

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)*sys.PtrSize))
	if sysauxv(auxv[:]) == 0 {
		// 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 := mmap(nil, size, _PROT_READ|_PROT_WRITE, _MAP_ANON|_MAP_PRIVATE, -1, 0)
			if uintptr(p) < 4096 {
				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[:])
	}
}

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
		}

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

func osinit() {
	ncpu = getproccount()
}

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

func getRandomData(r []byte) {
	if startupRandomData != nil {
		n := copy(r, startupRandomData)
		extendRandom(r, n)
		return
	}
	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()

	// for debuggers, in case cgo created the thread
	getg().m.procid = uint64(gettid())
}

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

func memlimit() uintptr {
	/*
		TODO: Convert to Go when something actually uses the result.

		Rlimit rl;
		extern byte runtime·text[], runtime·end[];
		uintptr used;

		if(runtime·getrlimit(RLIMIT_AS, &rl) != 0)
			return 0;
		if(rl.rlim_cur >= 0x7fffffff)
			return 0;

		// Estimate our VM footprint excluding the heap.
		// Not an exact science: use size of binary plus
		// some room for thread stacks.
		used = runtime·end - runtime·text + (64<<20);
		if(used >= rl.rlim_cur)
			return 0;

		// If there's not at least 16 MB left, we're probably
		// not going to be able to do much. Treat as no limit.
		rl.rlim_cur -= used;
		if(rl.rlim_cur < (16<<20))
			return 0;

		return rl.rlim_cur - used;
	*/

	return 0
}

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

func sigreturn()
func sigtramp(sig uint32, info *siginfo, ctx unsafe.Pointer)
func cgoSigtramp()

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

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

//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)))
}

//go:noescape
func getrlimit(kind int32, limit unsafe.Pointer) int32
func raise(sig uint32)
func raiseproc(sig uint32)

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

//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 = funcPC(sigreturn)
	}
	if fn == funcPC(sighandler) {
		if iscgo {
			fn = funcPC(cgoSigtramp)
		} else {
			fn = funcPC(sigtramp)
		}
	}
	sa.sa_handler = fn
	rt_sigaction(uintptr(i), &sa, nil, unsafe.Sizeof(sa.sa_mask))
}

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

//go:nosplit
//go:nowritebarrierrec
func getsig(i uint32) uintptr {
	var sa sigactiont
	if rt_sigaction(uintptr(i), nil, &sa, unsafe.Sizeof(sa.sa_mask)) != 0 {
		throw("rt_sigaction read failure")
	}
	return sa.sa_handler
}

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

func (c *sigctxt) fixsigcode(sig uint32) {
}