[gostls13.git] / src / runtime / runtime2.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/atomic"
        "unsafe"
)

/*
 * defined constants
 */
const (
        // G status
        //
        // If you add to this list, add to the list
        // of "okay during garbage collection" status
        // in mgcmark.go too.
        _Gidle            = iota // 0
        _Grunnable               // 1 runnable and on a run queue
        _Grunning                // 2
        _Gsyscall                // 3
        _Gwaiting                // 4
        _Gmoribund_unused        // 5 currently unused, but hardcoded in gdb scripts
        _Gdead                   // 6
        _Genqueue                // 7 Only the Gscanenqueue is used.
        _Gcopystack              // 8 in this state when newstack is moving the stack
        // the following encode that the GC is scanning the stack and what to do when it is done
        _Gscan = 0x1000 // atomicstatus&~Gscan = the non-scan state,
        // _Gscanidle =     _Gscan + _Gidle,      // Not used. Gidle only used with newly malloced gs
        _Gscanrunnable = _Gscan + _Grunnable //  0x1001 When scanning completes make Grunnable (it is already on run queue)
        _Gscanrunning  = _Gscan + _Grunning  //  0x1002 Used to tell preemption newstack routine to scan preempted stack.
        _Gscansyscall  = _Gscan + _Gsyscall  //  0x1003 When scanning completes make it Gsyscall
        _Gscanwaiting  = _Gscan + _Gwaiting  //  0x1004 When scanning completes make it Gwaiting
        // _Gscanmoribund_unused,               //  not possible
        // _Gscandead,                          //  not possible
        _Gscanenqueue = _Gscan + _Genqueue //  When scanning completes make it Grunnable and put on runqueue
)

const (
        // P status
        _Pidle    = iota
        _Prunning // Only this P is allowed to change from _Prunning.
        _Psyscall
        _Pgcstop
        _Pdead
)

// The next line makes 'go generate' write the zgen_*.go files with
// per-OS and per-arch information, including constants
// named goos_$GOOS and goarch_$GOARCH for every
// known GOOS and GOARCH. The constant is 1 on the
// current system, 0 otherwise; multiplying by them is
// useful for defining GOOS- or GOARCH-specific constants.
//go:generate go run gengoos.go

type mutex struct {
        // Futex-based impl treats it as uint32 key,
        // while sema-based impl as M* waitm.
        // Used to be a union, but unions break precise GC.
        key uintptr
}

type note struct {
        // Futex-based impl treats it as uint32 key,
        // while sema-based impl as M* waitm.
        // Used to be a union, but unions break precise GC.
        key uintptr
}

type funcval struct {
        fn uintptr
        // variable-size, fn-specific data here
}

type iface struct {
        tab  *itab
        data unsafe.Pointer
}

type eface struct {
        _type *_type
        data  unsafe.Pointer
}

func efaceOf(ep *interface{}) *eface {
        return (*eface)(unsafe.Pointer(ep))
}

// The guintptr, muintptr, and puintptr are all used to bypass write barriers.
// It is particularly important to avoid write barriers when the current P has
// been released, because the GC thinks the world is stopped, and an
// unexpected write barrier would not be synchronized with the GC,
// which can lead to a half-executed write barrier that has marked the object
// but not queued it. If the GC skips the object and completes before the
// queuing can occur, it will incorrectly free the object.
//
// We tried using special assignment functions invoked only when not
// holding a running P, but then some updates to a particular memory
// word went through write barriers and some did not. This breaks the
// write barrier shadow checking mode, and it is also scary: better to have
// a word that is completely ignored by the GC than to have one for which
// only a few updates are ignored.
//
// Gs, Ms, and Ps are always reachable via true pointers in the
// allgs, allm, and allp lists or (during allocation before they reach those lists)
// from stack variables.

// A guintptr holds a goroutine pointer, but typed as a uintptr
// to bypass write barriers. It is used in the Gobuf goroutine state
// and in scheduling lists that are manipulated without a P.
//
// The Gobuf.g goroutine pointer is almost always updated by assembly code.
// In one of the few places it is updated by Go code - func save - it must be
// treated as a uintptr to avoid a write barrier being emitted at a bad time.
// Instead of figuring out how to emit the write barriers missing in the
// assembly manipulation, we change the type of the field to uintptr,
// so that it does not require write barriers at all.
//
// Goroutine structs are published in the allg list and never freed.
// That will keep the goroutine structs from being collected.
// There is never a time that Gobuf.g's contain the only references
// to a goroutine: the publishing of the goroutine in allg comes first.
// Goroutine pointers are also kept in non-GC-visible places like TLS,
// so I can't see them ever moving. If we did want to start moving data
// in the GC, we'd need to allocate the goroutine structs from an
// alternate arena. Using guintptr doesn't make that problem any worse.
type guintptr uintptr

func (gp guintptr) ptr() *g   { return (*g)(unsafe.Pointer(gp)) }
func (gp *guintptr) set(g *g) { *gp = guintptr(unsafe.Pointer(g)) }
func (gp *guintptr) cas(old, new guintptr) bool {
        return atomic.Casuintptr((*uintptr)(unsafe.Pointer(gp)), uintptr(old), uintptr(new))
}

type puintptr uintptr

func (pp puintptr) ptr() *p   { return (*p)(unsafe.Pointer(pp)) }
func (pp *puintptr) set(p *p) { *pp = puintptr(unsafe.Pointer(p)) }

type muintptr uintptr

func (mp muintptr) ptr() *m   { return (*m)(unsafe.Pointer(mp)) }
func (mp *muintptr) set(m *m) { *mp = muintptr(unsafe.Pointer(m)) }

type gobuf struct {
        // The offsets of sp, pc, and g are known to (hard-coded in) libmach.
        sp   uintptr
        pc   uintptr
        g    guintptr
        ctxt unsafe.Pointer // this has to be a pointer so that gc scans it
        ret  uintreg
        lr   uintptr
        bp   uintptr // for GOEXPERIMENT=framepointer
}

// Known to compiler.
// Changes here must also be made in src/cmd/internal/gc/select.go's selecttype.
type sudog struct {
        g           *g
        selectdone  *uint32
        next        *sudog
        prev        *sudog
        elem        unsafe.Pointer // data element
        releasetime int64
        nrelease    int32  // -1 for acquire
        waitlink    *sudog // g.waiting list
}

type gcstats struct {
        // the struct must consist of only uint64's,
        // because it is casted to uint64[].
        nhandoff    uint64
        nhandoffcnt uint64
        nprocyield  uint64
        nosyield    uint64
        nsleep      uint64
}

type libcall struct {
        fn   uintptr
        n    uintptr // number of parameters
        args uintptr // parameters
        r1   uintptr // return values
        r2   uintptr
        err  uintptr // error number
}

// describes how to handle callback
type wincallbackcontext struct {
        gobody       unsafe.Pointer // go function to call
        argsize      uintptr        // callback arguments size (in bytes)
        restorestack uintptr        // adjust stack on return by (in bytes) (386 only)
        cleanstack   bool
}

// Stack describes a Go execution stack.
// The bounds of the stack are exactly [lo, hi),
// with no implicit data structures on either side.
type stack struct {
        lo uintptr
        hi uintptr
}

// stkbar records the state of a G's stack barrier.
type stkbar struct {
        savedLRPtr uintptr // location overwritten by stack barrier PC
        savedLRVal uintptr // value overwritten at savedLRPtr
}

type g struct {
        // Stack parameters.
        // stack describes the actual stack memory: [stack.lo, stack.hi).
        // stackguard0 is the stack pointer compared in the Go stack growth prologue.
        // It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption.
        // stackguard1 is the stack pointer compared in the C stack growth prologue.
        // It is stack.lo+StackGuard on g0 and gsignal stacks.
        // It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).
        stack       stack   // offset known to runtime/cgo
        stackguard0 uintptr // offset known to liblink
        stackguard1 uintptr // offset known to liblink

        _panic         *_panic // innermost panic - offset known to liblink
        _defer         *_defer // innermost defer
        m              *m      // current m; offset known to arm liblink
        stackAlloc     uintptr // stack allocation is [stack.lo,stack.lo+stackAlloc)
        sched          gobuf
        syscallsp      uintptr        // if status==Gsyscall, syscallsp = sched.sp to use during gc
        syscallpc      uintptr        // if status==Gsyscall, syscallpc = sched.pc to use during gc
        stkbar         []stkbar       // stack barriers, from low to high
        stkbarPos      uintptr        // index of lowest stack barrier not hit
        stktopsp       uintptr        // expected sp at top of stack, to check in traceback
        param          unsafe.Pointer // passed parameter on wakeup
        atomicstatus   uint32
        stackLock      uint32 // sigprof/scang lock; TODO: fold in to atomicstatus
        goid           int64
        waitsince      int64  // approx time when the g become blocked
        waitreason     string // if status==Gwaiting
        schedlink      guintptr
        preempt        bool   // preemption signal, duplicates stackguard0 = stackpreempt
        paniconfault   bool   // panic (instead of crash) on unexpected fault address
        preemptscan    bool   // preempted g does scan for gc
        gcscandone     bool   // g has scanned stack; protected by _Gscan bit in status
        gcscanvalid    bool   // false at start of gc cycle, true if G has not run since last scan
        throwsplit     bool   // must not split stack
        raceignore     int8   // ignore race detection events
        sysblocktraced bool   // StartTrace has emitted EvGoInSyscall about this goroutine
        sysexitticks   int64  // cputicks when syscall has returned (for tracing)
        sysexitseq     uint64 // trace seq when syscall has returned (for tracing)
        lockedm        *m
        sig            uint32
        writebuf       []byte
        sigcode0       uintptr
        sigcode1       uintptr
        sigpc          uintptr
        gopc           uintptr // pc of go statement that created this goroutine
        startpc        uintptr // pc of goroutine function
        racectx        uintptr
        waiting        *sudog // sudog structures this g is waiting on (that have a valid elem ptr)

        // Per-G gcController state

        // gcAssistBytes is this G's GC assist credit in terms of
        // bytes allocated. If this is positive, then the G has credit
        // to allocate gcAssistBytes bytes without assisting. If this
        // is negative, then the G must correct this by performing
        // scan work. We track this in bytes to make it fast to update
        // and check for debt in the malloc hot path. The assist ratio
        // determines how this corresponds to scan work debt.
        gcAssistBytes int64
}

type m struct {
        g0      *g     // goroutine with scheduling stack
        morebuf gobuf  // gobuf arg to morestack
        divmod  uint32 // div/mod denominator for arm - known to liblink

        // Fields not known to debuggers.
        procid        uint64     // for debuggers, but offset not hard-coded
        gsignal       *g         // signal-handling g
        sigmask       [4]uintptr // storage for saved signal mask
        tls           [4]uintptr // thread-local storage (for x86 extern register)
        mstartfn      func()
        curg          *g       // current running goroutine
        caughtsig     guintptr // goroutine running during fatal signal
        p             puintptr // attached p for executing go code (nil if not executing go code)
        nextp         puintptr
        id            int32
        mallocing     int32
        throwing      int32
        preemptoff    string // if != "", keep curg running on this m
        locks         int32
        softfloat     int32
        dying         int32
        profilehz     int32
        helpgc        int32
        spinning      bool // m is out of work and is actively looking for work
        blocked       bool // m is blocked on a note
        inwb          bool // m is executing a write barrier
        printlock     int8
        fastrand      uint32
        ncgocall      uint64 // number of cgo calls in total
        ncgo          int32  // number of cgo calls currently in progress
        park          note
        alllink       *m // on allm
        schedlink     muintptr
        machport      uint32 // return address for mach ipc (os x)
        mcache        *mcache
        lockedg       *g
        createstack   [32]uintptr // stack that created this thread.
        freglo        [16]uint32  // d[i] lsb and f[i]
        freghi        [16]uint32  // d[i] msb and f[i+16]
        fflag         uint32      // floating point compare flags
        locked        uint32      // tracking for lockosthread
        nextwaitm     uintptr     // next m waiting for lock
        waitsema      uintptr     // semaphore for parking on locks
        waitsemacount uint32
        waitsemalock  uint32
        gcstats       gcstats
        needextram    bool
        traceback     uint8
        waitunlockf   unsafe.Pointer // todo go func(*g, unsafe.pointer) bool
        waitlock      unsafe.Pointer
        waittraceev   byte
        waittraceskip int
        startingtrace bool
        syscalltick   uint32
        //#ifdef GOOS_windows
        thread uintptr // thread handle
        // these are here because they are too large to be on the stack
        // of low-level NOSPLIT functions.
        libcall   libcall
        libcallpc uintptr // for cpu profiler
        libcallsp uintptr
        libcallg  guintptr
        syscall   libcall // stores syscall parameters on windows
        //#endif
        mOS
}

type p struct {
        lock mutex

        id          int32
        status      uint32 // one of pidle/prunning/...
        link        puintptr
        schedtick   uint32   // incremented on every scheduler call
        syscalltick uint32   // incremented on every system call
        m           muintptr // back-link to associated m (nil if idle)
        mcache      *mcache

        deferpool    [5][]*_defer // pool of available defer structs of different sizes (see panic.go)
        deferpoolbuf [5][32]*_defer

        // Cache of goroutine ids, amortizes accesses to runtime·sched.goidgen.
        goidcache    uint64
        goidcacheend uint64

        // Queue of runnable goroutines. Accessed without lock.
        runqhead uint32
        runqtail uint32
        runq     [256]guintptr
        // runnext, if non-nil, is a runnable G that was ready'd by
        // the current G and should be run next instead of what's in
        // runq if there's time remaining in the running G's time
        // slice. It will inherit the time left in the current time
        // slice. If a set of goroutines is locked in a
        // communicate-and-wait pattern, this schedules that set as a
        // unit and eliminates the (potentially large) scheduling
        // latency that otherwise arises from adding the ready'd
        // goroutines to the end of the run queue.
        runnext guintptr

        // Available G's (status == Gdead)
        gfree    *g
        gfreecnt int32

        sudogcache []*sudog
        sudogbuf   [128]*sudog

        tracebuf traceBufPtr

        palloc persistentAlloc // per-P to avoid mutex

        // Per-P GC state
        gcAssistTime     int64 // Nanoseconds in assistAlloc
        gcBgMarkWorker   *g
        gcMarkWorkerMode gcMarkWorkerMode

        // gcw is this P's GC work buffer cache. The work buffer is
        // filled by write barriers, drained by mutator assists, and
        // disposed on certain GC state transitions.
        gcw gcWork

        runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point

        pad [64]byte
}

const (
        // The max value of GOMAXPROCS.
        // There are no fundamental restrictions on the value.
        _MaxGomaxprocs = 1 << 8
)

type schedt struct {
        lock mutex

        goidgen uint64

        midle        muintptr // idle m's waiting for work
        nmidle       int32    // number of idle m's waiting for work
        nmidlelocked int32    // number of locked m's waiting for work
        mcount       int32    // number of m's that have been created
        maxmcount    int32    // maximum number of m's allowed (or die)

        pidle      puintptr // idle p's
        npidle     uint32
        nmspinning uint32 // limited to [0, 2^31-1]

        // Global runnable queue.
        runqhead guintptr
        runqtail guintptr
        runqsize int32

        // Global cache of dead G's.
        gflock mutex
        gfree  *g
        ngfree int32

        // Central cache of sudog structs.
        sudoglock  mutex
        sudogcache *sudog

        // Central pool of available defer structs of different sizes.
        deferlock mutex
        deferpool [5]*_defer

        gcwaiting  uint32 // gc is waiting to run
        stopwait   int32
        stopnote   note
        sysmonwait uint32
        sysmonnote note
        lastpoll   uint64

        // safepointFn should be called on each P at the next GC
        // safepoint if p.runSafePointFn is set.
        safePointFn   func(*p)
        safePointWait int32
        safePointNote note

        profilehz int32 // cpu profiling rate

        procresizetime int64 // nanotime() of last change to gomaxprocs
        totaltime      int64 // ∫gomaxprocs dt up to procresizetime
}

// The m->locked word holds two pieces of state counting active calls to LockOSThread/lockOSThread.
// The low bit (LockExternal) is a boolean reporting whether any LockOSThread call is active.
// External locks are not recursive; a second lock is silently ignored.
// The upper bits of m->locked record the nesting depth of calls to lockOSThread
// (counting up by LockInternal), popped by unlockOSThread (counting down by LockInternal).
// Internal locks can be recursive. For instance, a lock for cgo can occur while the main
// goroutine is holding the lock during the initialization phase.
const (
        _LockExternal = 1
        _LockInternal = 2
)

type sigtabtt struct {
        flags int32
        name  *int8
}

const (
        _SigNotify   = 1 << iota // let signal.Notify have signal, even if from kernel
        _SigKill                 // if signal.Notify doesn't take it, exit quietly
        _SigThrow                // if signal.Notify doesn't take it, exit loudly
        _SigPanic                // if the signal is from the kernel, panic
        _SigDefault              // if the signal isn't explicitly requested, don't monitor it
        _SigHandling             // our signal handler is registered
        _SigIgnored              // the signal was ignored before we registered for it
        _SigGoExit               // cause all runtime procs to exit (only used on Plan 9).
        _SigSetStack             // add SA_ONSTACK to libc handler
        _SigUnblock              // unblocked in minit
)

// Layout of in-memory per-function information prepared by linker
// See https://golang.org/s/go12symtab.
// Keep in sync with linker
// and with package debug/gosym and with symtab.go in package runtime.
type _func struct {
        entry   uintptr // start pc
        nameoff int32   // function name

        args int32 // in/out args size
        _    int32 // Previously: legacy frame size. TODO: Remove this.

        pcsp      int32
        pcfile    int32
        pcln      int32
        npcdata   int32
        nfuncdata int32
}

// layout of Itab known to compilers
// allocated in non-garbage-collected memory
type itab struct {
        inter  *interfacetype
        _type  *_type
        link   *itab
        bad    int32
        unused int32
        fun    [1]uintptr // variable sized
}

// Lock-free stack node.
// // Also known to export_test.go.
type lfnode struct {
        next    uint64
        pushcnt uintptr
}

type forcegcstate struct {
        lock mutex
        g    *g
        idle uint32
}

/*
 * known to compiler
 */
const (
        _Structrnd = regSize
)

// startup_random_data holds random bytes initialized at startup.  These come from
// the ELF AT_RANDOM auxiliary vector (vdso_linux_amd64.go or os_linux_386.go).
var startupRandomData []byte

// extendRandom extends the random numbers in r[:n] to the whole slice r.
// Treats n<0 as n==0.
func extendRandom(r []byte, n int) {
        if n < 0 {
                n = 0
        }
        for n < len(r) {
                // Extend random bits using hash function & time seed
                w := n
                if w > 16 {
                        w = 16
                }
                h := memhash(unsafe.Pointer(&r[n-w]), uintptr(nanotime()), uintptr(w))
                for i := 0; i < ptrSize && n < len(r); i++ {
                        r[n] = byte(h)
                        n++
                        h >>= 8
                }
        }
}

/*
 * deferred subroutine calls
 */
type _defer struct {
        siz     int32
        started bool
        sp      uintptr // sp at time of defer
        pc      uintptr
        fn      *funcval
        _panic  *_panic // panic that is running defer
        link    *_defer
}

/*
 * panics
 */
type _panic struct {
        argp      unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblink
        arg       interface{}    // argument to panic
        link      *_panic        // link to earlier panic
        recovered bool           // whether this panic is over
        aborted   bool           // the panic was aborted
}

/*
 * stack traces
 */

type stkframe struct {
        fn       *_func     // function being run
        pc       uintptr    // program counter within fn
        continpc uintptr    // program counter where execution can continue, or 0 if not
        lr       uintptr    // program counter at caller aka link register
        sp       uintptr    // stack pointer at pc
        fp       uintptr    // stack pointer at caller aka frame pointer
        varp     uintptr    // top of local variables
        argp     uintptr    // pointer to function arguments
        arglen   uintptr    // number of bytes at argp
        argmap   *bitvector // force use of this argmap
}

const (
        _TraceRuntimeFrames = 1 << iota // include frames for internal runtime functions.
        _TraceTrap                      // the initial PC, SP are from a trap, not a return PC from a call
        _TraceJumpStack                 // if traceback is on a systemstack, resume trace at g that called into it
)

const (
        // The maximum number of frames we print for a traceback
        _TracebackMaxFrames = 100
)

var (
        emptystring string
        allglen     uintptr
        allm        *m
        allp        [_MaxGomaxprocs + 1]*p
        gomaxprocs  int32
        panicking   uint32
        ncpu        int32
        forcegc     forcegcstate
        sched       schedt
        newprocs    int32

        // Information about what cpu features are available.
        // Set on startup in asm_{x86,amd64}.s.
        cpuid_ecx         uint32
        cpuid_edx         uint32
        lfenceBeforeRdtsc bool
        support_avx       bool
        support_avx2      bool

        goarm uint8 // set by cmd/link on arm systems
)

// Set by the linker so the runtime can determine the buildmode.
var (
        islibrary bool // -buildmode=c-shared
        isarchive bool // -buildmode=c-archive
)

/*
 * mutual exclusion locks.  in the uncontended case,
 * as fast as spin locks (just a few user-level instructions),
 * but on the contention path they sleep in the kernel.
 * a zeroed Mutex is unlocked (no need to initialize each lock).
 */

/*
 * sleep and wakeup on one-time events.
 * before any calls to notesleep or notewakeup,
 * must call noteclear to initialize the Note.
 * then, exactly one thread can call notesleep
 * and exactly one thread can call notewakeup (once).
 * once notewakeup has been called, the notesleep
 * will return.  future notesleep will return immediately.
 * subsequent noteclear must be called only after
 * previous notesleep has returned, e.g. it's disallowed
 * to call noteclear straight after notewakeup.
 *
 * notetsleep is like notesleep but wakes up after
 * a given number of nanoseconds even if the event
 * has not yet happened.  if a goroutine uses notetsleep to
 * wake up early, it must wait to call noteclear until it
 * can be sure that no other goroutine is calling
 * notewakeup.
 *
 * notesleep/notetsleep are generally called on g0,
 * notetsleepg is similar to notetsleep but is called on user g.
 */
// bool runtime·notetsleep(Note*, int64);  // false - timeout
// bool runtime·notetsleepg(Note*, int64);  // false - timeout

/*
 * Lock-free stack.
 * Initialize uint64 head to 0, compare with 0 to test for emptiness.
 * The stack does not keep pointers to nodes,
 * so they can be garbage collected if there are no other pointers to nodes.
 */

// for mmap, we only pass the lower 32 bits of file offset to the
// assembly routine; the higher bits (if required), should be provided
// by the assembly routine as 0.