src/runtime/stubs.go

// Copyright 2014 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 (
	"internal/abi"
	"internal/goarch"
	"internal/goexperiment"
	"unsafe"
)

// Should be a built-in for unsafe.Pointer?
//go:nosplit
func add(p unsafe.Pointer, x uintptr) unsafe.Pointer {
	return unsafe.Pointer(uintptr(p) + x)
}

// getg returns the pointer to the current g.
// The compiler rewrites calls to this function into instructions
// that fetch the g directly (from TLS or from the dedicated register).
func getg() *g

// mcall switches from the g to the g0 stack and invokes fn(g),
// where g is the goroutine that made the call.
// mcall saves g's current PC/SP in g->sched so that it can be restored later.
// It is up to fn to arrange for that later execution, typically by recording
// g in a data structure, causing something to call ready(g) later.
// mcall returns to the original goroutine g later, when g has been rescheduled.
// fn must not return at all; typically it ends by calling schedule, to let the m
// run other goroutines.
//
// mcall can only be called from g stacks (not g0, not gsignal).
//
// This must NOT be go:noescape: if fn is a stack-allocated closure,
// fn puts g on a run queue, and g executes before fn returns, the
// closure will be invalidated while it is still executing.
func mcall(fn func(*g))

// systemstack runs fn on a system stack.
// If systemstack is called from the per-OS-thread (g0) stack, or
// if systemstack is called from the signal handling (gsignal) stack,
// systemstack calls fn directly and returns.
// Otherwise, systemstack is being called from the limited stack
// of an ordinary goroutine. In this case, systemstack switches
// to the per-OS-thread stack, calls fn, and switches back.
// It is common to use a func literal as the argument, in order
// to share inputs and outputs with the code around the call
// to system stack:
//
//	... set up y ...
//	systemstack(func() {
//		x = bigcall(y)
//	})
//	... use x ...
//
//go:noescape
func systemstack(fn func())

var badsystemstackMsg = "fatal: systemstack called from unexpected goroutine"

//go:nosplit
//go:nowritebarrierrec
func badsystemstack() {
	sp := stringStructOf(&badsystemstackMsg)
	write(2, sp.str, int32(sp.len))
}

// memclrNoHeapPointers clears n bytes starting at ptr.
//
// Usually you should use typedmemclr. memclrNoHeapPointers should be
// used only when the caller knows that *ptr contains no heap pointers
// because either:
//
// *ptr is initialized memory and its type is pointer-free, or
//
// *ptr is uninitialized memory (e.g., memory that's being reused
// for a new allocation) and hence contains only "junk".
//
// memclrNoHeapPointers ensures that if ptr is pointer-aligned, and n
// is a multiple of the pointer size, then any pointer-aligned,
// pointer-sized portion is cleared atomically. Despite the function
// name, this is necessary because this function is the underlying
// implementation of typedmemclr and memclrHasPointers. See the doc of
// memmove for more details.
//
// The (CPU-specific) implementations of this function are in memclr_*.s.
//
//go:noescape
func memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr)

//go:linkname reflect_memclrNoHeapPointers reflect.memclrNoHeapPointers
func reflect_memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr) {
	memclrNoHeapPointers(ptr, n)
}

// memmove copies n bytes from "from" to "to".
//
// memmove ensures that any pointer in "from" is written to "to" with
// an indivisible write, so that racy reads cannot observe a
// half-written pointer. This is necessary to prevent the garbage
// collector from observing invalid pointers, and differs from memmove
// in unmanaged languages. However, memmove is only required to do
// this if "from" and "to" may contain pointers, which can only be the
// case if "from", "to", and "n" are all be word-aligned.
//
// Implementations are in memmove_*.s.
//
//go:noescape
func memmove(to, from unsafe.Pointer, n uintptr)

// Outside assembly calls memmove. Make sure it has ABI wrappers.
//go:linkname memmove

//go:linkname reflect_memmove reflect.memmove
func reflect_memmove(to, from unsafe.Pointer, n uintptr) {
	memmove(to, from, n)
}

// exported value for testing
const hashLoad = float32(loadFactorNum) / float32(loadFactorDen)

//go:nosplit
func fastrand() uint32 {
	mp := getg().m
	// Implement xorshift64+: 2 32-bit xorshift sequences added together.
	// Shift triplet [17,7,16] was calculated as indicated in Marsaglia's
	// Xorshift paper: https://www.jstatsoft.org/article/view/v008i14/xorshift.pdf
	// This generator passes the SmallCrush suite, part of TestU01 framework:
	// http://simul.iro.umontreal.ca/testu01/tu01.html
	s1, s0 := mp.fastrand[0], mp.fastrand[1]
	s1 ^= s1 << 17
	s1 = s1 ^ s0 ^ s1>>7 ^ s0>>16
	mp.fastrand[0], mp.fastrand[1] = s0, s1
	return s0 + s1
}

//go:nosplit
func fastrandn(n uint32) uint32 {
	// This is similar to fastrand() % n, but faster.
	// See https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
	return uint32(uint64(fastrand()) * uint64(n) >> 32)
}

//go:linkname sync_fastrand sync.fastrand
func sync_fastrand() uint32 { return fastrand() }

//go:linkname net_fastrand net.fastrand
func net_fastrand() uint32 { return fastrand() }

//go:linkname os_fastrand os.fastrand
func os_fastrand() uint32 { return fastrand() }

// in internal/bytealg/equal_*.s
//go:noescape
func memequal(a, b unsafe.Pointer, size uintptr) bool

// noescape hides a pointer from escape analysis.  noescape is
// the identity function but escape analysis doesn't think the
// output depends on the input.  noescape is inlined and currently
// compiles down to zero instructions.
// USE CAREFULLY!
//go:nosplit
func noescape(p unsafe.Pointer) unsafe.Pointer {
	x := uintptr(p)
	return unsafe.Pointer(x ^ 0)
}

// Not all cgocallback frames are actually cgocallback,
// so not all have these arguments. Mark them uintptr so that the GC
// does not misinterpret memory when the arguments are not present.
// cgocallback is not called from Go, only from crosscall2.
// This in turn calls cgocallbackg, which is where we'll find
// pointer-declared arguments.
func cgocallback(fn, frame, ctxt uintptr)

func gogo(buf *gobuf)

func asminit()
func setg(gg *g)
func breakpoint()

// reflectcall calls fn with arguments described by stackArgs, stackArgsSize,
// frameSize, and regArgs.
//
// Arguments passed on the stack and space for return values passed on the stack
// must be laid out at the space pointed to by stackArgs (with total length
// stackArgsSize) according to the ABI.
//
// stackRetOffset must be some value <= stackArgsSize that indicates the
// offset within stackArgs where the return value space begins.
//
// frameSize is the total size of the argument frame at stackArgs and must
// therefore be >= stackArgsSize. It must include additional space for spilling
// register arguments for stack growth and preemption.
//
// TODO(mknyszek): Once we don't need the additional spill space, remove frameSize,
// since frameSize will be redundant with stackArgsSize.
//
// Arguments passed in registers must be laid out in regArgs according to the ABI.
// regArgs will hold any return values passed in registers after the call.
//
// reflectcall copies stack arguments from stackArgs to the goroutine stack, and
// then copies back stackArgsSize-stackRetOffset bytes back to the return space
// in stackArgs once fn has completed. It also "unspills" argument registers from
// regArgs before calling fn, and spills them back into regArgs immediately
// following the call to fn. If there are results being returned on the stack,
// the caller should pass the argument frame type as stackArgsType so that
// reflectcall can execute appropriate write barriers during the copy.
//
// reflectcall expects regArgs.ReturnIsPtr to be populated indicating which
// registers on the return path will contain Go pointers. It will then store
// these pointers in regArgs.Ptrs such that they are visible to the GC.
//
// Package reflect passes a frame type. In package runtime, there is only
// one call that copies results back, in callbackWrap in syscall_windows.go, and it
// does NOT pass a frame type, meaning there are no write barriers invoked. See that
// call site for justification.
//
// Package reflect accesses this symbol through a linkname.
//
// Arguments passed through to reflectcall do not escape. The type is used
// only in a very limited callee of reflectcall, the stackArgs are copied, and
// regArgs is only used in the reflectcall frame.
//go:noescape
func reflectcall(stackArgsType *_type, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)

func procyield(cycles uint32)

type neverCallThisFunction struct{}

// goexit is the return stub at the top of every goroutine call stack.
// Each goroutine stack is constructed as if goexit called the
// goroutine's entry point function, so that when the entry point
// function returns, it will return to goexit, which will call goexit1
// to perform the actual exit.
//
// This function must never be called directly. Call goexit1 instead.
// gentraceback assumes that goexit terminates the stack. A direct
// call on the stack will cause gentraceback to stop walking the stack
// prematurely and if there is leftover state it may panic.
func goexit(neverCallThisFunction)

// publicationBarrier performs a store/store barrier (a "publication"
// or "export" barrier). Some form of synchronization is required
// between initializing an object and making that object accessible to
// another processor. Without synchronization, the initialization
// writes and the "publication" write may be reordered, allowing the
// other processor to follow the pointer and observe an uninitialized
// object. In general, higher-level synchronization should be used,
// such as locking or an atomic pointer write. publicationBarrier is
// for when those aren't an option, such as in the implementation of
// the memory manager.
//
// There's no corresponding barrier for the read side because the read
// side naturally has a data dependency order. All architectures that
// Go supports or seems likely to ever support automatically enforce
// data dependency ordering.
func publicationBarrier()

// getcallerpc returns the program counter (PC) of its caller's caller.
// getcallersp returns the stack pointer (SP) of its caller's caller.
// The implementation may be a compiler intrinsic; there is not
// necessarily code implementing this on every platform.
//
// For example:
//
//	func f(arg1, arg2, arg3 int) {
//		pc := getcallerpc()
//		sp := getcallersp()
//	}
//
// These two lines find the PC and SP immediately following
// the call to f (where f will return).
//
// The call to getcallerpc and getcallersp must be done in the
// frame being asked about.
//
// The result of getcallersp is correct at the time of the return,
// but it may be invalidated by any subsequent call to a function
// that might relocate the stack in order to grow or shrink it.
// A general rule is that the result of getcallersp should be used
// immediately and can only be passed to nosplit functions.

//go:noescape
func getcallerpc() uintptr

//go:noescape
func getcallersp() uintptr // implemented as an intrinsic on all platforms

// getclosureptr returns the pointer to the current closure.
// getclosureptr can only be used in an assignment statement
// at the entry of a function. Moreover, go:nosplit directive
// must be specified at the declaration of caller function,
// so that the function prolog does not clobber the closure register.
// for example:
//
//	//go:nosplit
//	func f(arg1, arg2, arg3 int) {
//		dx := getclosureptr()
//	}
//
// The compiler rewrites calls to this function into instructions that fetch the
// pointer from a well-known register (DX on x86 architecture, etc.) directly.
func getclosureptr() uintptr

//go:noescape
func asmcgocall(fn, arg unsafe.Pointer) int32

func morestack()
func morestack_noctxt()
func rt0_go()

// return0 is a stub used to return 0 from deferproc.
// It is called at the very end of deferproc to signal
// the calling Go function that it should not jump
// to deferreturn.
// in asm_*.s
func return0()

// in asm_*.s
// not called directly; definitions here supply type information for traceback.
// These must have the same signature (arg pointer map) as reflectcall.
func call16(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call32(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call64(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call128(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call256(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call512(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call1024(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call2048(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call4096(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call8192(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call16384(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call32768(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call65536(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call131072(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call262144(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call524288(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call1048576(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call2097152(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call4194304(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call8388608(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call16777216(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call33554432(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call67108864(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call134217728(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call268435456(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call536870912(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)
func call1073741824(typ, fn, stackArgs unsafe.Pointer, stackArgsSize, stackRetOffset, frameSize uint32, regArgs *abi.RegArgs)

func systemstack_switch()

// alignUp rounds n up to a multiple of a. a must be a power of 2.
func alignUp(n, a uintptr) uintptr {
	return (n + a - 1) &^ (a - 1)
}

// alignDown rounds n down to a multiple of a. a must be a power of 2.
func alignDown(n, a uintptr) uintptr {
	return n &^ (a - 1)
}

// divRoundUp returns ceil(n / a).
func divRoundUp(n, a uintptr) uintptr {
	// a is generally a power of two. This will get inlined and
	// the compiler will optimize the division.
	return (n + a - 1) / a
}

// checkASM reports whether assembly runtime checks have passed.
func checkASM() bool

func memequal_varlen(a, b unsafe.Pointer) bool

// bool2int returns 0 if x is false or 1 if x is true.
func bool2int(x bool) int {
	// Avoid branches. In the SSA compiler, this compiles to
	// exactly what you would want it to.
	return int(uint8(*(*uint8)(unsafe.Pointer(&x))))
}

// abort crashes the runtime in situations where even throw might not
// work. In general it should do something a debugger will recognize
// (e.g., an INT3 on x86). A crash in abort is recognized by the
// signal handler, which will attempt to tear down the runtime
// immediately.
func abort()

// Called from compiled code; declared for vet; do NOT call from Go.
func gcWriteBarrier()
func duffzero()
func duffcopy()

// Called from linker-generated .initarray; declared for go vet; do NOT call from Go.
func addmoduledata()

// Injected by the signal handler for panicking signals.
// Initializes any registers that have fixed meaning at calls but
// are scratch in bodies and calls sigpanic.
// On many platforms it just jumps to sigpanic.
func sigpanic0()

// intArgRegs is used by the various register assignment
// algorithm implementations in the runtime. These include:.
// - Finalizers (mfinal.go)
// - Windows callbacks (syscall_windows.go)
//
// Both are stripped-down versions of the algorithm since they
// only have to deal with a subset of cases (finalizers only
// take a pointer or interface argument, Go Windows callbacks
// don't support floating point).
//
// It should be modified with care and are generally only
// modified when testing this package.
//
// It should never be set higher than its internal/abi
// constant counterparts, because the system relies on a
// structure that is at least large enough to hold the
// registers the system supports.
//
// Protected by finlock.
var intArgRegs = abi.IntArgRegs * (goexperiment.RegabiArgsInt | goarch.IsAmd64)