[go-nuts] What will happen if the go and cgo's malloc return overlapped ?

[Remus Clearwater]

>From this thread 
<https://groups.google.com/forum/#!topic/golang-nuts/KyXR0fDp0HA>, we know:

> The GC ignores pointers it knows nothing about. (by Ian)

So we have this code in cmd/cgo/out.go 
<https://github.com/golang/go/blob/57fa1c7c949c5ea1efd756e2ed0c4442998690a9/src/cmd/cgo/out.go#L1450>
:

func _Cfunc_CString(s string) *_Ctype_char {
    p := _cgo_cmalloc(uint64(len(s)+1))
    pp := (*[1<<30]byte)(p)
    copy(pp[:], s)
    pp[len(s)] = 0
    return (*_Ctype_char)(p)
}

But what will happend if the go and cgo's malloc overlapped?
(Not meantime, but in a moderated time interval that may happen.)

Example:

{
    p := C.malloc(uintptr(1024*1024)) // this is C.malloc
    pp := (*[1<<30]byte)(p)
    doSomething(pp,1024*1024)
}

{
    b:=SomeBigObject{} // go malloc
}

runtime.GC()

// this is the 1st GC after the pp being new-ed in go land so far.
// but what will happen if the underlying memory address of pp == b's ?
// the gc might find two totally different go objects which has the 
// same underlying memory address.
// what is the gc's behaviour in this circumstance? could this lead 
// to some unexpected bugs ? 

Thanks a lot.

Enjoy!

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