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    Metadata details:
    filename: mbarrier.go
    path of file: ./repos/gccrs/libgo/go/runtime
    
    the code of the file until where you have to start completion: // Copyright 2015 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.

// Garbage collector: write barriers.
//
// For the concurrent garbage collector, the Go compiler implements
// updates to pointer-valued fields that may be in heap objects by
// emitting calls to write barriers. The main write barrier for
// individual pointer writes is gcWriteBarrier and is implemented in
// assembly. This file contains write barrier entry points for bulk
// operations. See also mwbbuf.go.

package runtime

import (
	"internal/abi"
	"internal/goarch"
	"unsafe"
)

// For gccgo, use go:linkname to export compiler-called functions.
//
//go:linkname typedmemmove
//go:linkname typedslicecopy
//go:linkname memclrHasPointers

// Go uses a hybrid barrier that combines a Yuasa-style deletion
// barrier—which shades the object whose reference is being
// overwritten—with Dijkstra insertion barrier—which shades the object
// whose reference is being written. The insertion part of the barrier
// is necessary while the calling goroutine's stack is grey. In
// pseudocode
    
func typedslicecopy(typ *_type, dstPtr unsafe.Pointer, dstLen int, srcPtr unsafe.Pointer, srcLen int) int {
	n := dstLen
	if n > srcLen {
		n = srcLen
	}
	if n == 0 {
		return 0
	}

	// The compiler emits calls to typedslicecopy before
	// instrumentation runs, so unlike the other copying and
	// assignment operations, it's not instrumented in the calling
	// code and needs its own instrumentation.
	if raceenabled {
		callerpc := getcallerpc()
		pc := abi.FuncPCABIInternal(slicecopy)
		racewriterangepc(dstPtr, uintptr(n)*typ.size, callerpc, pc)
		racereadrangepc(srcPtr, uintptr(n)*typ.size, callerpc, pc)
	}
	if msanenabled {
		msanwrite(dstPtr, uintptr(n)*typ.size)
		msanread(srcPtr, uintptr(n)*typ.size)
	}
	if asanenabled {
		asanwrite(dstPtr, uintptr(n)*typ.size)
		asanread(srcPtr, uintptr(n)*typ.size)
	}

	if writeBarrier.cgo {
		cgoCheckSliceCopy(typ, dstPtr, srcPtr, n)
	}

	if dstPtr == srcPtr {
		return n
	}

	// Note: No point in checking typ.ptrdata here:
	// compiler only emits calls to typedslicecopy for types with pointers,
	// and growslice and reflect_typedslicecopy check for pointers
	// before calling typedslicecopy.
	size := uintptr(n) * typ.size
	if writeBarrier.needed {
		pwsize := size - typ.size + typ.ptrdata
		bulkBarrierPreWrite(uintptr(dstPtr), uintptr(srcPtr), pwsize)
	}
	// See typedmemmove for a discussion of the race between the
	// barrier and memmove.
	memmove(dstPtr, srcPtr, size)
	return n
}