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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 when GOEXPERIMENT=cgocheck2 is enabled.
package runtime
import (
"internal/goarch"
"internal/goexperiment"
"unsafe"
)
const cgoWriteBarrierFail = "unpinned Go pointer stored into non-Go memory"
// cgoCheckPtrWrite is called whenever a pointer is stored into memory.
// It throws if the program is storing an unpinned Go pointer into non-Go
// memory.
//
// This is called from generated code when GOEXPERIMENT=cgocheck2 is enabled.
//
//go:nosplit
//go:nowritebarrier
func cgoCheckPtrWrite(dst *unsafe.Pointer, src unsafe.Pointer) {
if !mainStarted {
// Something early in startup hates this function.
// Don't start doing any actual checking until the
// runtime has set itself up.
return
}
if !cgoIsGoPointer(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.
gp := getg()
if gp == gp.m.g0 || gp == gp.m.gsignal {
return
}
// Allocating memory can write to various mfixalloc structs
// that look like they are non-Go memory.
if gp.m.mallocing != 0 {
return
}
// If the object is pinned, it's safe to store it in C memory. The GC
// ensures it will not be moved or freed.
if isPinned(src) {
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 unpinned Go pointer", hex(uintptr(src)), "to non-Go memory", hex(uintptr(unsafe.Pointer(dst))))
throw(cgoWriteBarrierFail)
})
}
// cgoCheckMemmove is called when moving a block of memory.
// It throws if the program is copying a block that contains an unpinned Go
// pointer into non-Go memory.
//
// This is called from generated code when GOEXPERIMENT=cgocheck2 is enabled.
//
//go:nosplit
//go:nowritebarrier
func cgoCheckMemmove(typ *_type, dst, src unsafe.Pointer) {
cgoCheckMemmove2(typ, dst, src, 0, typ.Size_)
}
// cgoCheckMemmove2 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 an unpinned Go
// pointer into non-Go memory.
//
//go:nosplit
//go:nowritebarrier
func cgoCheckMemmove2(typ *_type, dst, src unsafe.Pointer, off, size uintptr) {
if typ.PtrBytes == 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.
// src and dst are pointers to the first element of the slice.
// typ is the element type of the slice.
// It throws if the program is copying slice elements that contain unpinned Go
// pointers into non-Go memory.
//
//go:nosplit
//go:nowritebarrier
func cgoCheckSliceCopy(typ *_type, dst, src unsafe.Pointer, n int) {
if typ.PtrBytes == 0 {
return
}
if !cgoIsGoPointer(src) {
return
}
if cgoIsGoPointer(dst) {
return
}
p := src
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 an unpinned 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.PtrBytes is not a pointer.
if typ.PtrBytes <= off {
return
}
if ptrdataSize := typ.PtrBytes - 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.
for _, datap := range activeModules() {
if cgoInRange(src, datap.data, datap.edata) {
doff := uintptr(src) - datap.data
cgoCheckBits(add(src, -doff), datap.gcdatamask.bytedata, off+doff, size)
return
}
if cgoInRange(src, datap.bss, datap.ebss) {
boff := uintptr(src) - datap.bss
cgoCheckBits(add(src, -boff), datap.gcbssmask.bytedata, off+boff, size)
return
}
}
s := spanOfUnchecked(uintptr(src))
if s.state.get() == 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.
if goexperiment.AllocHeaders {
tp := s.typePointersOf(uintptr(src), size)
for {
var addr uintptr
if tp, addr = tp.next(uintptr(src) + size); addr == 0 {
break
}
v := *(*unsafe.Pointer)(unsafe.Pointer(addr))
if cgoIsGoPointer(v) && !isPinned(v) {
throw(cgoWriteBarrierFail)
}
}
} else {
hbits := heapBitsForAddr(uintptr(src), size)
for {
var addr uintptr
if hbits, addr = hbits.next(); addr == 0 {
break
}
v := *(*unsafe.Pointer)(unsafe.Pointer(addr))
if cgoIsGoPointer(v) && !isPinned(v) {
throw(cgoWriteBarrierFail)
}
}
}
}
// cgoCheckBits checks the block of memory at src, for up to size
// bytes, and throws if it finds an unpinned 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 / goarch.PtrSize / 8
skipBytes := skipMask * goarch.PtrSize * 8
ptrmask := addb(gcbits, skipMask)
src = add(src, skipBytes)
off -= skipBytes
size += off
var bits uint32
for i := uintptr(0); i < size; i += goarch.PtrSize {
if i&(goarch.PtrSize*8-1) == 0 {
bits = uint32(*ptrmask)
ptrmask = addb(ptrmask, 1)
} else {
bits >>= 1
}
if off > 0 {
off -= goarch.PtrSize
} else {
if bits&1 != 0 {
v := *(*unsafe.Pointer)(add(src, i))
if cgoIsGoPointer(v) && !isPinned(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.PtrBytes == 0 {
return
}
// Anything past typ.PtrBytes is not a pointer.
if typ.PtrBytes <= off {
return
}
if ptrdataSize := typ.PtrBytes - 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
}
}
}