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// 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
}
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.kind&kindNoPointers != 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.kind&kindNoPointers != 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.kind&kindNoPointers != 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
}
}
}