libgo/go/runtime/cgocall.go - gofrontend - Git at Google

 // 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.

 // Cgo call and callback support.

 package runtime

 import (
 	"runtime/internal/sys"
 	"unsafe"
 )

 // Functions called by cgo-generated code.
 //go:linkname cgoCheckPointer runtime.cgoCheckPointer
 //go:linkname cgoCheckResult runtime.cgoCheckResult

 // Pointer checking for cgo code.

 // We want to detect all cases where a program that does not use
 // unsafe makes a cgo call passing a Go pointer to memory that
 // contains a Go pointer. Here a Go pointer is defined as a pointer
 // to memory allocated by the Go runtime. Programs that use unsafe
 // can evade this restriction easily, so we don't try to catch them.
 // The cgo program will rewrite all possibly bad pointer arguments to
 // call cgoCheckPointer, where we can catch cases of a Go pointer
 // pointing to a Go pointer.

 // Complicating matters, taking the address of a slice or array
 // element permits the C program to access all elements of the slice
 // or array. In that case we will see a pointer to a single element,
 // but we need to check the entire data structure.

 // The cgoCheckPointer call takes additional arguments indicating that
 // it was called on an address expression. An additional argument of
 // true means that it only needs to check a single element. An
 // additional argument of a slice or array means that it needs to
 // check the entire slice/array, but nothing else. Otherwise, the
 // pointer could be anything, and we check the entire heap object,
 // which is conservative but safe.

 // When and if we implement a moving garbage collector,
 // cgoCheckPointer will pin the pointer for the duration of the cgo
 // call.  (This is necessary but not sufficient; the cgo program will
 // also have to change to pin Go pointers that cannot point to Go
 // pointers.)

 // cgoCheckPointer checks if the argument contains a Go pointer that
 // points to a Go pointer, and panics if it does.
 func cgoCheckPointer(ptr interface{}, args ...interface{}) {
 	if debug.cgocheck == 0 {
 		return
 	}

 	ep := (*eface)(unsafe.Pointer(&ptr))
 	t := ep._type

 	top := true
 	if len(args) > 0 && (t.kind&kindMask == kindPtr || t.kind&kindMask == kindUnsafePointer) {
 		p := ep.data
 		if t.kind&kindDirectIface == 0 {
 			p = *(*unsafe.Pointer)(p)
 		}
 		if !cgoIsGoPointer(p) {
 			return
 		}
 		aep := (*eface)(unsafe.Pointer(&args[0]))
 		switch aep._type.kind & kindMask {
 		case kindBool:
 			if t.kind&kindMask == kindUnsafePointer {
 				// We don't know the type of the element.
 				break
 			}
 			pt := (*ptrtype)(unsafe.Pointer(t))
 			cgoCheckArg(pt.elem, p, true, false, cgoCheckPointerFail)
 			return
 		case kindSlice:
 			// Check the slice rather than the pointer.
 			ep = aep
 			t = ep._type
 		case kindArray:
 			// Check the array rather than the pointer.
 			// Pass top as false since we have a pointer
 			// to the array.
 			ep = aep
 			t = ep._type
 			top = false
 		default:
 			throw("can't happen")
 		}
 	}

 	cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, top, cgoCheckPointerFail)
 }

 const cgoCheckPointerFail = "cgo argument has Go pointer to Go pointer"
 const cgoResultFail = "cgo result has Go pointer"

 // cgoCheckArg is the real work of cgoCheckPointer. The argument p
 // is either a pointer to the value (of type t), or the value itself,
 // depending on indir. The top parameter is whether we are at the top
 // level, where Go pointers are allowed.
 func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) {
 	if t.kind&kindNoPointers != 0 {
 		// If the type has no pointers there is nothing to do.
 		return
 	}

 	switch t.kind & kindMask {
 	default:
 		throw("can't happen")
 	case kindArray:
 		at := (*arraytype)(unsafe.Pointer(t))
 		if !indir {
 			if at.len != 1 {
 				throw("can't happen")
 			}
 			cgoCheckArg(at.elem, p, at.elem.kind&kindDirectIface == 0, top, msg)
 			return
 		}
 		for i := uintptr(0); i < at.len; i++ {
 			cgoCheckArg(at.elem, p, true, top, msg)
 			p = add(p, at.elem.size)
 		}
 	case kindChan, kindMap:
 		// These types contain internal pointers that will
 		// always be allocated in the Go heap. It's never OK
 		// to pass them to C.
 		panic(errorString(msg))
 	case kindFunc:
 		if indir {
 			p = *(*unsafe.Pointer)(p)
 		}
 		if !cgoIsGoPointer(p) {
 			return
 		}
 		panic(errorString(msg))
 	case kindInterface:
 		it := *(**_type)(p)
 		if it == nil {
 			return
 		}
 		// A type known at compile time is OK since it's
 		// constant. A type not known at compile time will be
 		// in the heap and will not be OK.
 		if inheap(uintptr(unsafe.Pointer(it))) {
 			panic(errorString(msg))
 		}
 		p = *(*unsafe.Pointer)(add(p, sys.PtrSize))
 		if !cgoIsGoPointer(p) {
 			return
 		}
 		if !top {
 			panic(errorString(msg))
 		}
 		cgoCheckArg(it, p, it.kind&kindDirectIface == 0, false, msg)
 	case kindSlice:
 		st := (*slicetype)(unsafe.Pointer(t))
 		s := (*slice)(p)
 		p = s.array
 		if !cgoIsGoPointer(p) {
 			return
 		}
 		if !top {
 			panic(errorString(msg))
 		}
 		if st.elem.kind&kindNoPointers != 0 {
 			return
 		}
 		for i := 0; i < s.cap; i++ {
 			cgoCheckArg(st.elem, p, true, false, msg)
 			p = add(p, st.elem.size)
 		}
 	case kindString:
 		ss := (*stringStruct)(p)
 		if !cgoIsGoPointer(ss.str) {
 			return
 		}
 		if !top {
 			panic(errorString(msg))
 		}
 	case kindStruct:
 		st := (*structtype)(unsafe.Pointer(t))
 		if !indir {
 			if len(st.fields) != 1 {
 				throw("can't happen")
 			}
 			cgoCheckArg(st.fields[0].typ, p, st.fields[0].typ.kind&kindDirectIface == 0, top, msg)
 			return
 		}
 		for _, f := range st.fields {
 			cgoCheckArg(f.typ, add(p, f.offset()), true, top, msg)
 		}
 	case kindPtr, kindUnsafePointer:
 		if indir {
 			p = *(*unsafe.Pointer)(p)
 		}

 		if !cgoIsGoPointer(p) {
 			return
 		}
 		if !top {
 			panic(errorString(msg))
 		}

 		cgoCheckUnknownPointer(p, msg)
 	}
 }

 // cgoCheckUnknownPointer is called for an arbitrary pointer into Go
 // memory. It checks whether that Go memory contains any other
 // pointer into Go memory. If it does, we panic.
 // The return values are unused but useful to see in panic tracebacks.
 func cgoCheckUnknownPointer(p unsafe.Pointer, msg string) (base, i uintptr) {
 	if inheap(uintptr(p)) {
 		b, span, _ := findObject(uintptr(p), 0, 0, false)
 		base = b
 		if base == 0 {
 			return
 		}
 		hbits := heapBitsForAddr(base)
 		n := span.elemsize
 		for i = uintptr(0); i < n; i += sys.PtrSize {
 			if i != 1*sys.PtrSize && !hbits.morePointers() {
 				// No more possible pointers.
 				break
 			}
 			if hbits.isPointer() && cgoIsGoPointer(*(*unsafe.Pointer)(unsafe.Pointer(base + i))) {
 				panic(errorString(msg))
 			}
 			hbits = hbits.next()
 		}

 		return
 	}

 	lo := 0
 	hi := len(gcRootsIndex)
 	for lo < hi {
 		m := lo + (hi-lo)/2
 		pr := gcRootsIndex[m]
 		addr := uintptr(pr.decl)
 		if cgoInRange(p, addr, addr+pr.size) {
 			cgoCheckBits(pr.decl, pr.gcdata, 0, pr.ptrdata)
 			return
 		}
 		if uintptr(p) < addr {
 			hi = m
 		} else {
 			lo = m + 1
 		}
 	}

 	return
 }

 // cgoIsGoPointer returns whether the pointer is a Go pointer--a
 // pointer to Go memory. We only care about Go memory that might
 // contain pointers.
 //go:nosplit
 //go:nowritebarrierrec
 func cgoIsGoPointer(p unsafe.Pointer) bool {
 	if p == nil {
 		return false
 	}

 	if inHeapOrStack(uintptr(p)) {
 		return true
 	}

 	roots := gcRoots
 	for roots != nil {
 		for i := 0; i < roots.count; i++ {
 			pr := roots.roots[i]
 			addr := uintptr(pr.decl)
 			if cgoInRange(p, addr, addr+pr.size) {
 				return true
 			}
 		}
 		roots = roots.next
 	}

 	return false
 }

 // cgoInRange returns whether p is between start and end.
 //go:nosplit
 //go:nowritebarrierrec
 func cgoInRange(p unsafe.Pointer, start, end uintptr) bool {
 	return start <= uintptr(p) && uintptr(p) < end
 }

 // cgoCheckResult is called to check the result parameter of an
 // exported Go function. It panics if the result is or contains a Go
 // pointer.
 func cgoCheckResult(val interface{}) {
 	if debug.cgocheck == 0 {
 		return
 	}

 	ep := (*eface)(unsafe.Pointer(&val))
 	t := ep._type
 	cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, false, cgoResultFail)
 }
	// 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.

	// Cgo call and callback support.

	package runtime

	import (
	"runtime/internal/sys"
	"unsafe"
	)

	// Functions called by cgo-generated code.
	//go:linkname cgoCheckPointer runtime.cgoCheckPointer
	//go:linkname cgoCheckResult runtime.cgoCheckResult

	// Pointer checking for cgo code.

	// We want to detect all cases where a program that does not use
	// unsafe makes a cgo call passing a Go pointer to memory that
	// contains a Go pointer. Here a Go pointer is defined as a pointer
	// to memory allocated by the Go runtime. Programs that use unsafe
	// can evade this restriction easily, so we don't try to catch them.
	// The cgo program will rewrite all possibly bad pointer arguments to
	// call cgoCheckPointer, where we can catch cases of a Go pointer
	// pointing to a Go pointer.

	// Complicating matters, taking the address of a slice or array
	// element permits the C program to access all elements of the slice
	// or array. In that case we will see a pointer to a single element,
	// but we need to check the entire data structure.

	// The cgoCheckPointer call takes additional arguments indicating that
	// it was called on an address expression. An additional argument of
	// true means that it only needs to check a single element. An
	// additional argument of a slice or array means that it needs to
	// check the entire slice/array, but nothing else. Otherwise, the
	// pointer could be anything, and we check the entire heap object,
	// which is conservative but safe.

	// When and if we implement a moving garbage collector,
	// cgoCheckPointer will pin the pointer for the duration of the cgo
	// call. (This is necessary but not sufficient; the cgo program will
	// also have to change to pin Go pointers that cannot point to Go
	// pointers.)

	// cgoCheckPointer checks if the argument contains a Go pointer that
	// points to a Go pointer, and panics if it does.
	func cgoCheckPointer(ptr interface{}, args ...interface{}) {
	if debug.cgocheck == 0 {
	return
	}

	ep := (*eface)(unsafe.Pointer(&ptr))
	t := ep._type

	top := true
	if len(args) > 0 && (t.kind&kindMask == kindPtr \|\| t.kind&kindMask == kindUnsafePointer) {
	p := ep.data
	if t.kind&kindDirectIface == 0 {
	p = (unsafe.Pointer)(p)
	}
	if !cgoIsGoPointer(p) {
	return
	}
	aep := (*eface)(unsafe.Pointer(&args[0]))
	switch aep._type.kind & kindMask {
	case kindBool:
	if t.kind&kindMask == kindUnsafePointer {
	// We don't know the type of the element.
	break
	}
	pt := (*ptrtype)(unsafe.Pointer(t))
	cgoCheckArg(pt.elem, p, true, false, cgoCheckPointerFail)
	return
	case kindSlice:
	// Check the slice rather than the pointer.
	ep = aep
	t = ep._type
	case kindArray:
	// Check the array rather than the pointer.
	// Pass top as false since we have a pointer
	// to the array.
	ep = aep
	t = ep._type
	top = false
	default:
	throw("can't happen")
	}
	}

	cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, top, cgoCheckPointerFail)
	}

	const cgoCheckPointerFail = "cgo argument has Go pointer to Go pointer"
	const cgoResultFail = "cgo result has Go pointer"

	// cgoCheckArg is the real work of cgoCheckPointer. The argument p
	// is either a pointer to the value (of type t), or the value itself,
	// depending on indir. The top parameter is whether we are at the top
	// level, where Go pointers are allowed.
	func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) {
	if t.kind&kindNoPointers != 0 {
	// If the type has no pointers there is nothing to do.
	return
	}

	switch t.kind & kindMask {
	default:
	throw("can't happen")
	case kindArray:
	at := (*arraytype)(unsafe.Pointer(t))
	if !indir {
	if at.len != 1 {
	throw("can't happen")
	}
	cgoCheckArg(at.elem, p, at.elem.kind&kindDirectIface == 0, top, msg)
	return
	}
	for i := uintptr(0); i < at.len; i++ {
	cgoCheckArg(at.elem, p, true, top, msg)
	p = add(p, at.elem.size)
	}
	case kindChan, kindMap:
	// These types contain internal pointers that will
	// always be allocated in the Go heap. It's never OK
	// to pass them to C.
	panic(errorString(msg))
	case kindFunc:
	if indir {
	p = (unsafe.Pointer)(p)
	}
	if !cgoIsGoPointer(p) {
	return
	}
	panic(errorString(msg))
	case kindInterface:
	it := (*_type)(p)
	if it == nil {
	return
	}
	// A type known at compile time is OK since it's
	// constant. A type not known at compile time will be
	// in the heap and will not be OK.
	if inheap(uintptr(unsafe.Pointer(it))) {
	panic(errorString(msg))
	}
	p = (unsafe.Pointer)(add(p, sys.PtrSize))
	if !cgoIsGoPointer(p) {
	return
	}
	if !top {
	panic(errorString(msg))
	}
	cgoCheckArg(it, p, it.kind&kindDirectIface == 0, false, msg)
	case kindSlice:
	st := (*slicetype)(unsafe.Pointer(t))
	s := (*slice)(p)
	p = s.array
	if !cgoIsGoPointer(p) {
	return
	}
	if !top {
	panic(errorString(msg))
	}
	if st.elem.kind&kindNoPointers != 0 {
	return
	}
	for i := 0; i < s.cap; i++ {
	cgoCheckArg(st.elem, p, true, false, msg)
	p = add(p, st.elem.size)
	}
	case kindString:
	ss := (*stringStruct)(p)
	if !cgoIsGoPointer(ss.str) {
	return
	}
	if !top {
	panic(errorString(msg))
	}
	case kindStruct:
	st := (*structtype)(unsafe.Pointer(t))
	if !indir {
	if len(st.fields) != 1 {
	throw("can't happen")
	}
	cgoCheckArg(st.fields[0].typ, p, st.fields[0].typ.kind&kindDirectIface == 0, top, msg)
	return
	}
	for _, f := range st.fields {
	cgoCheckArg(f.typ, add(p, f.offset()), true, top, msg)
	}
	case kindPtr, kindUnsafePointer:
	if indir {
	p = (unsafe.Pointer)(p)
	}

	if !cgoIsGoPointer(p) {
	return
	}
	if !top {
	panic(errorString(msg))
	}

	cgoCheckUnknownPointer(p, msg)
	}
	}

	// cgoCheckUnknownPointer is called for an arbitrary pointer into Go
	// memory. It checks whether that Go memory contains any other
	// pointer into Go memory. If it does, we panic.
	// The return values are unused but useful to see in panic tracebacks.
	func cgoCheckUnknownPointer(p unsafe.Pointer, msg string) (base, i uintptr) {
	if inheap(uintptr(p)) {
	b, span, _ := findObject(uintptr(p), 0, 0, false)
	base = b
	if base == 0 {
	return
	}
	hbits := heapBitsForAddr(base)
	n := span.elemsize
	for i = uintptr(0); i < n; i += sys.PtrSize {
	if i != 1*sys.PtrSize && !hbits.morePointers() {
	// No more possible pointers.
	break
	}
	if hbits.isPointer() && cgoIsGoPointer((unsafe.Pointer)(unsafe.Pointer(base + i))) {
	panic(errorString(msg))
	}
	hbits = hbits.next()
	}

	return
	}

	lo := 0
	hi := len(gcRootsIndex)
	for lo < hi {
	m := lo + (hi-lo)/2
	pr := gcRootsIndex[m]
	addr := uintptr(pr.decl)
	if cgoInRange(p, addr, addr+pr.size) {
	cgoCheckBits(pr.decl, pr.gcdata, 0, pr.ptrdata)
	return
	}
	if uintptr(p) < addr {
	hi = m
	} else {
	lo = m + 1
	}
	}

	return
	}

	// cgoIsGoPointer returns whether the pointer is a Go pointer--a
	// pointer to Go memory. We only care about Go memory that might
	// contain pointers.
	//go:nosplit
	//go:nowritebarrierrec
	func cgoIsGoPointer(p unsafe.Pointer) bool {
	if p == nil {
	return false
	}

	if inHeapOrStack(uintptr(p)) {
	return true
	}

	roots := gcRoots
	for roots != nil {
	for i := 0; i < roots.count; i++ {
	pr := roots.roots[i]
	addr := uintptr(pr.decl)
	if cgoInRange(p, addr, addr+pr.size) {
	return true
	}
	}
	roots = roots.next
	}

	return false
	}

	// cgoInRange returns whether p is between start and end.
	//go:nosplit
	//go:nowritebarrierrec
	func cgoInRange(p unsafe.Pointer, start, end uintptr) bool {
	return start <= uintptr(p) && uintptr(p) < end
	}

	// cgoCheckResult is called to check the result parameter of an
	// exported Go function. It panics if the result is or contains a Go
	// pointer.
	func cgoCheckResult(val interface{}) {
	if debug.cgocheck == 0 {
	return
	}

	ep := (*eface)(unsafe.Pointer(&val))
	t := ep._type
	cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, false, cgoResultFail)
	}