Source: stubs.go in package runtime


package runtime

import "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:nosplitgo: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)

go:linkname reflect_memmove reflect.memmove

func reflect_memmove(to, from unsafe.Pointer, n uintptr) {
	memmove(to, from, n)
}

exported value for testing

var hashLoad = float32(loadFactorNum) / float32(loadFactorDen)

go:nosplit

func fastrand() uint32 {

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

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_*.sgo: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 gosave(buf *gobuf)

go:noescape

func jmpdefer(fv *funcval, argp uintptr)
func asminit()
func setg(gg *g)
func breakpoint()

reflectcall calls fn with a copy of the n argument bytes pointed at by arg. After fn returns, reflectcall copies n-retoffset result bytes back into arg+retoffset before returning. If copying result bytes back, the caller should pass the argument frame type as argtype, so that call can execute appropriate write barriers during the copy. Package reflect always passes a frame type. In package runtime, Windows callbacks are the only use of this that copies results back, and those cannot have pointers in their results, so runtime passes nil for the frame type. Package reflect accesses this symbol through a linkname.

func reflectcall(argtype *_type, fn, arg unsafe.Pointer, argsize uint32, retoffset uint32)

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.

func call16(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call32(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call64(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call128(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call256(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call512(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call1024(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call2048(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call4096(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call8192(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call16384(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call32768(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call65536(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call131072(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call262144(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call524288(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call1048576(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call2097152(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call4194304(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call8388608(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call16777216(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call33554432(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call67108864(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call134217728(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call268435456(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call536870912(typ, fn, arg unsafe.Pointer, n, retoffset uint32)
func call1073741824(typ, fn, arg unsafe.Pointer, n, retoffset uint32)

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).

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.

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.