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

 // 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.

 // Code to check that pointer writes follow the cgo rules.
 // These functions are invoked via the write barrier when debug.cgocheck > 1.

 package runtime

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

 const cgoWriteBarrierFail = "Go pointer stored into non-Go memory"

 // cgoCheckWriteBarrier is called whenever a pointer is stored into memory.
 // It throws if the program is storing a Go pointer into non-Go memory.
 //
 // This is called from the write barrier, so its entire call tree must
 // be nosplit.
 //
 //go:nosplit
 //go:nowritebarrier
 func cgoCheckWriteBarrier(dst *uintptr, src uintptr) {
 	if !cgoIsGoPointer(unsafe.Pointer(src)) {
 		return
 	}
 	if cgoIsGoPointer(unsafe.Pointer(dst)) {
 		return
 	}

 	// If we are running on the system stack then dst might be an
 	// address on the stack, which is OK.
 	g := getg()
 	if g == g.m.g0 || g == g.m.gsignal {
 		return
 	}

 	// Allocating memory can write to various mfixalloc structs
 	// that look like they are non-Go memory.
 	if g.m.mallocing != 0 {
 		return
 	}

 	// It's OK if writing to memory allocated by persistentalloc.
 	// Do this check last because it is more expensive and rarely true.
 	// If it is false the expense doesn't matter since we are crashing.
 	if inPersistentAlloc(uintptr(unsafe.Pointer(dst))) {
 		return
 	}

 	systemstack(func() {
 		println("write of Go pointer", hex(src), "to non-Go memory", hex(uintptr(unsafe.Pointer(dst))))
 		throw(cgoWriteBarrierFail)
 	})
 }

 // cgoCheckMemmove is called when moving a block of memory.
 // dst and src point off bytes into the value to copy.
 // size is the number of bytes to copy.
 // It throws if the program is copying a block that contains a Go pointer
 // into non-Go memory.
 //go:nosplit
 //go:nowritebarrier
 func cgoCheckMemmove(typ *_type, dst, src unsafe.Pointer, off, size uintptr) {
 	if typ.ptrdata == 0 {
 		return
 	}
 	if !cgoIsGoPointer(src) {
 		return
 	}
 	if cgoIsGoPointer(dst) {
 		return
 	}
 	cgoCheckTypedBlock(typ, src, off, size)
 }

 // cgoCheckSliceCopy is called when copying n elements of a slice from
 // src to dst.  typ is the element type of the slice.
 // It throws if the program is copying slice elements that contain Go pointers
 // into non-Go memory.
 //go:nosplit
 //go:nowritebarrier
 func cgoCheckSliceCopy(typ *_type, dst, src slice, n int) {
 	if typ.ptrdata == 0 {
 		return
 	}
 	if !cgoIsGoPointer(src.array) {
 		return
 	}
 	if cgoIsGoPointer(dst.array) {
 		return
 	}
 	p := src.array
 	for i := 0; i < n; i++ {
 		cgoCheckTypedBlock(typ, p, 0, typ.size)
 		p = add(p, typ.size)
 	}
 }

 // cgoCheckTypedBlock checks the block of memory at src, for up to size bytes,
 // and throws if it finds a Go pointer. The type of the memory is typ,
 // and src is off bytes into that type.
 //go:nosplit
 //go:nowritebarrier
 func cgoCheckTypedBlock(typ *_type, src unsafe.Pointer, off, size uintptr) {
 	// Anything past typ.ptrdata is not a pointer.
 	if typ.ptrdata <= off {
 		return
 	}
 	if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
 		size = ptrdataSize
 	}

 	if typ.kind&kindGCProg == 0 {
 		cgoCheckBits(src, typ.gcdata, off, size)
 		return
 	}

 	// The type has a GC program. Try to find GC bits somewhere else.
 	roots := gcRoots
 	for roots != nil {
 		for i := 0; i < roots.count; i++ {
 			pr := roots.roots[i]
 			addr := uintptr(pr.decl)
 			if cgoInRange(src, addr, addr+pr.size) {
 				doff := uintptr(src) - addr
 				cgoCheckBits(add(src, -doff), pr.gcdata, off+doff, size)
 				return
 			}
 		}
 		roots = roots.next
 	}

 	s := spanOfUnchecked(uintptr(src))
 	if s.state == mSpanManual {
 		// There are no heap bits for value stored on the stack.
 		// For a channel receive src might be on the stack of some
 		// other goroutine, so we can't unwind the stack even if
 		// we wanted to.
 		// We can't expand the GC program without extra storage
 		// space we can't easily get.
 		// Fortunately we have the type information.
 		systemstack(func() {
 			cgoCheckUsingType(typ, src, off, size)
 		})
 		return
 	}

 	// src must be in the regular heap.

 	hbits := heapBitsForAddr(uintptr(src))
 	for i := uintptr(0); i < off+size; i += sys.PtrSize {
 		bits := hbits.bits()
 		if i >= off && bits&bitPointer != 0 {
 			v := *(*unsafe.Pointer)(add(src, i))
 			if cgoIsGoPointer(v) {
 				throw(cgoWriteBarrierFail)
 			}
 		}
 		hbits = hbits.next()
 	}
 }

 // cgoCheckBits checks the block of memory at src, for up to size
 // bytes, and throws if it finds a Go pointer. The gcbits mark each
 // pointer value. The src pointer is off bytes into the gcbits.
 //go:nosplit
 //go:nowritebarrier
 func cgoCheckBits(src unsafe.Pointer, gcbits *byte, off, size uintptr) {
 	skipMask := off / sys.PtrSize / 8
 	skipBytes := skipMask * sys.PtrSize * 8
 	ptrmask := addb(gcbits, skipMask)
 	src = add(src, skipBytes)
 	off -= skipBytes
 	size += off
 	var bits uint32
 	for i := uintptr(0); i < size; i += sys.PtrSize {
 		if i&(sys.PtrSize*8-1) == 0 {
 			bits = uint32(*ptrmask)
 			ptrmask = addb(ptrmask, 1)
 		} else {
 			bits >>= 1
 		}
 		if off > 0 {
 			off -= sys.PtrSize
 		} else {
 			if bits&1 != 0 {
 				v := *(*unsafe.Pointer)(add(src, i))
 				if cgoIsGoPointer(v) {
 					throw(cgoWriteBarrierFail)
 				}
 			}
 		}
 	}
 }

 // cgoCheckUsingType is like cgoCheckTypedBlock, but is a last ditch
 // fall back to look for pointers in src using the type information.
 // We only use this when looking at a value on the stack when the type
 // uses a GC program, because otherwise it's more efficient to use the
 // GC bits. This is called on the system stack.
 //go:nowritebarrier
 //go:systemstack
 func cgoCheckUsingType(typ *_type, src unsafe.Pointer, off, size uintptr) {
 	if typ.ptrdata == 0 {
 		return
 	}

 	// Anything past typ.ptrdata is not a pointer.
 	if typ.ptrdata <= off {
 		return
 	}
 	if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
 		size = ptrdataSize
 	}

 	if typ.kind&kindGCProg == 0 {
 		cgoCheckBits(src, typ.gcdata, off, size)
 		return
 	}
 	switch typ.kind & kindMask {
 	default:
 		throw("can't happen")
 	case kindArray:
 		at := (*arraytype)(unsafe.Pointer(typ))
 		for i := uintptr(0); i < at.len; i++ {
 			if off < at.elem.size {
 				cgoCheckUsingType(at.elem, src, off, size)
 			}
 			src = add(src, at.elem.size)
 			skipped := off
 			if skipped > at.elem.size {
 				skipped = at.elem.size
 			}
 			checked := at.elem.size - skipped
 			off -= skipped
 			if size <= checked {
 				return
 			}
 			size -= checked
 		}
 	case kindStruct:
 		st := (*structtype)(unsafe.Pointer(typ))
 		for _, f := range st.fields {
 			if off < f.typ.size {
 				cgoCheckUsingType(f.typ, src, off, size)
 			}
 			src = add(src, f.typ.size)
 			skipped := off
 			if skipped > f.typ.size {
 				skipped = f.typ.size
 			}
 			checked := f.typ.size - skipped
 			off -= skipped
 			if size <= checked {
 				return
 			}
 			size -= checked
 		}
 	}
 }
	// 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.

	// Code to check that pointer writes follow the cgo rules.
	// These functions are invoked via the write barrier when debug.cgocheck > 1.

	package runtime

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

	const cgoWriteBarrierFail = "Go pointer stored into non-Go memory"

	// cgoCheckWriteBarrier is called whenever a pointer is stored into memory.
	// It throws if the program is storing a Go pointer into non-Go memory.
	//
	// This is called from the write barrier, so its entire call tree must
	// be nosplit.
	//
	//go:nosplit
	//go:nowritebarrier
	func cgoCheckWriteBarrier(dst *uintptr, src uintptr) {
	if !cgoIsGoPointer(unsafe.Pointer(src)) {
	return
	}
	if cgoIsGoPointer(unsafe.Pointer(dst)) {
	return
	}

	// If we are running on the system stack then dst might be an
	// address on the stack, which is OK.
	g := getg()
	if g == g.m.g0 \|\| g == g.m.gsignal {
	return
	}

	// Allocating memory can write to various mfixalloc structs
	// that look like they are non-Go memory.
	if g.m.mallocing != 0 {
	return
	}

	// It's OK if writing to memory allocated by persistentalloc.
	// Do this check last because it is more expensive and rarely true.
	// If it is false the expense doesn't matter since we are crashing.
	if inPersistentAlloc(uintptr(unsafe.Pointer(dst))) {
	return
	}

	systemstack(func() {
	println("write of Go pointer", hex(src), "to non-Go memory", hex(uintptr(unsafe.Pointer(dst))))
	throw(cgoWriteBarrierFail)
	})
	}

	// cgoCheckMemmove is called when moving a block of memory.
	// dst and src point off bytes into the value to copy.
	// size is the number of bytes to copy.
	// It throws if the program is copying a block that contains a Go pointer
	// into non-Go memory.
	//go:nosplit
	//go:nowritebarrier
	func cgoCheckMemmove(typ *_type, dst, src unsafe.Pointer, off, size uintptr) {
	if typ.ptrdata == 0 {
	return
	}
	if !cgoIsGoPointer(src) {
	return
	}
	if cgoIsGoPointer(dst) {
	return
	}
	cgoCheckTypedBlock(typ, src, off, size)
	}

	// cgoCheckSliceCopy is called when copying n elements of a slice from
	// src to dst. typ is the element type of the slice.
	// It throws if the program is copying slice elements that contain Go pointers
	// into non-Go memory.
	//go:nosplit
	//go:nowritebarrier
	func cgoCheckSliceCopy(typ *_type, dst, src slice, n int) {
	if typ.ptrdata == 0 {
	return
	}
	if !cgoIsGoPointer(src.array) {
	return
	}
	if cgoIsGoPointer(dst.array) {
	return
	}
	p := src.array
	for i := 0; i < n; i++ {
	cgoCheckTypedBlock(typ, p, 0, typ.size)
	p = add(p, typ.size)
	}
	}

	// cgoCheckTypedBlock checks the block of memory at src, for up to size bytes,
	// and throws if it finds a Go pointer. The type of the memory is typ,
	// and src is off bytes into that type.
	//go:nosplit
	//go:nowritebarrier
	func cgoCheckTypedBlock(typ *_type, src unsafe.Pointer, off, size uintptr) {
	// Anything past typ.ptrdata is not a pointer.
	if typ.ptrdata <= off {
	return
	}
	if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
	size = ptrdataSize
	}

	if typ.kind&kindGCProg == 0 {
	cgoCheckBits(src, typ.gcdata, off, size)
	return
	}

	// The type has a GC program. Try to find GC bits somewhere else.
	roots := gcRoots
	for roots != nil {
	for i := 0; i < roots.count; i++ {
	pr := roots.roots[i]
	addr := uintptr(pr.decl)
	if cgoInRange(src, addr, addr+pr.size) {
	doff := uintptr(src) - addr
	cgoCheckBits(add(src, -doff), pr.gcdata, off+doff, size)
	return
	}
	}
	roots = roots.next
	}

	s := spanOfUnchecked(uintptr(src))
	if s.state == mSpanManual {
	// There are no heap bits for value stored on the stack.
	// For a channel receive src might be on the stack of some
	// other goroutine, so we can't unwind the stack even if
	// we wanted to.
	// We can't expand the GC program without extra storage
	// space we can't easily get.
	// Fortunately we have the type information.
	systemstack(func() {
	cgoCheckUsingType(typ, src, off, size)
	})
	return
	}

	// src must be in the regular heap.

	hbits := heapBitsForAddr(uintptr(src))
	for i := uintptr(0); i < off+size; i += sys.PtrSize {
	bits := hbits.bits()
	if i >= off && bits&bitPointer != 0 {
	v := (unsafe.Pointer)(add(src, i))
	if cgoIsGoPointer(v) {
	throw(cgoWriteBarrierFail)
	}
	}
	hbits = hbits.next()
	}
	}

	// cgoCheckBits checks the block of memory at src, for up to size
	// bytes, and throws if it finds a Go pointer. The gcbits mark each
	// pointer value. The src pointer is off bytes into the gcbits.
	//go:nosplit
	//go:nowritebarrier
	func cgoCheckBits(src unsafe.Pointer, gcbits *byte, off, size uintptr) {
	skipMask := off / sys.PtrSize / 8
	skipBytes := skipMask * sys.PtrSize * 8
	ptrmask := addb(gcbits, skipMask)
	src = add(src, skipBytes)
	off -= skipBytes
	size += off
	var bits uint32
	for i := uintptr(0); i < size; i += sys.PtrSize {
	if i&(sys.PtrSize*8-1) == 0 {
	bits = uint32(*ptrmask)
	ptrmask = addb(ptrmask, 1)
	} else {
	bits >>= 1
	}
	if off > 0 {
	off -= sys.PtrSize
	} else {
	if bits&1 != 0 {
	v := (unsafe.Pointer)(add(src, i))
	if cgoIsGoPointer(v) {
	throw(cgoWriteBarrierFail)
	}
	}
	}
	}
	}

	// cgoCheckUsingType is like cgoCheckTypedBlock, but is a last ditch
	// fall back to look for pointers in src using the type information.
	// We only use this when looking at a value on the stack when the type
	// uses a GC program, because otherwise it's more efficient to use the
	// GC bits. This is called on the system stack.
	//go:nowritebarrier
	//go:systemstack
	func cgoCheckUsingType(typ *_type, src unsafe.Pointer, off, size uintptr) {
	if typ.ptrdata == 0 {
	return
	}

	// Anything past typ.ptrdata is not a pointer.
	if typ.ptrdata <= off {
	return
	}
	if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
	size = ptrdataSize
	}

	if typ.kind&kindGCProg == 0 {
	cgoCheckBits(src, typ.gcdata, off, size)
	return
	}
	switch typ.kind & kindMask {
	default:
	throw("can't happen")
	case kindArray:
	at := (*arraytype)(unsafe.Pointer(typ))
	for i := uintptr(0); i < at.len; i++ {
	if off < at.elem.size {
	cgoCheckUsingType(at.elem, src, off, size)
	}
	src = add(src, at.elem.size)
	skipped := off
	if skipped > at.elem.size {
	skipped = at.elem.size
	}
	checked := at.elem.size - skipped
	off -= skipped
	if size <= checked {
	return
	}
	size -= checked
	}
	case kindStruct:
	st := (*structtype)(unsafe.Pointer(typ))
	for _, f := range st.fields {
	if off < f.typ.size {
	cgoCheckUsingType(f.typ, src, off, size)
	}
	src = add(src, f.typ.size)
	skipped := off
	if skipped > f.typ.size {
	skipped = f.typ.size
	}
	checked := f.typ.size - skipped
	off -= skipped
	if size <= checked {
	return
	}
	size -= checked
	}
	}
	}