264 lines
6.8 KiB
Go
264 lines
6.8 KiB
Go
// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Code to check that pointer writes follow the cgo rules.
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// These functions are invoked via the write barrier when debug.cgocheck > 1.
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package runtime
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import (
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"internal/goarch"
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"unsafe"
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)
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const cgoWriteBarrierFail = "Go pointer stored into non-Go memory"
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// cgoCheckWriteBarrier is called whenever a pointer is stored into memory.
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// It throws if the program is storing a Go pointer into non-Go memory.
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//
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// This is called from the write barrier, so its entire call tree must
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// be nosplit.
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//
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//go:nosplit
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//go:nowritebarrier
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func cgoCheckWriteBarrier(dst *uintptr, src uintptr) {
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if !cgoIsGoPointer(unsafe.Pointer(src)) {
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return
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}
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if cgoIsGoPointer(unsafe.Pointer(dst)) {
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return
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}
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// If we are running on the system stack then dst might be an
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// address on the stack, which is OK.
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g := getg()
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if g == g.m.g0 || g == g.m.gsignal {
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return
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}
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// Allocating memory can write to various mfixalloc structs
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// that look like they are non-Go memory.
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if g.m.mallocing != 0 {
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return
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}
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// It's OK if writing to memory allocated by persistentalloc.
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// Do this check last because it is more expensive and rarely true.
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// If it is false the expense doesn't matter since we are crashing.
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if inPersistentAlloc(uintptr(unsafe.Pointer(dst))) {
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return
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}
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systemstack(func() {
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println("write of Go pointer", hex(src), "to non-Go memory", hex(uintptr(unsafe.Pointer(dst))))
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throw(cgoWriteBarrierFail)
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})
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}
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// cgoCheckMemmove is called when moving a block of memory.
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// dst and src point off bytes into the value to copy.
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// size is the number of bytes to copy.
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// It throws if the program is copying a block that contains a Go pointer
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// into non-Go memory.
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//go:nosplit
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//go:nowritebarrier
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func cgoCheckMemmove(typ *_type, dst, src unsafe.Pointer, off, size uintptr) {
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if typ.ptrdata == 0 {
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return
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}
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if !cgoIsGoPointer(src) {
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return
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}
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if cgoIsGoPointer(dst) {
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return
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}
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cgoCheckTypedBlock(typ, src, off, size)
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}
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// cgoCheckSliceCopy is called when copying n elements of a slice.
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// src and dst are pointers to the first element of the slice.
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// typ is the element type of the slice.
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// It throws if the program is copying slice elements that contain Go pointers
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// into non-Go memory.
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//go:nosplit
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//go:nowritebarrier
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func cgoCheckSliceCopy(typ *_type, dst, src unsafe.Pointer, n int) {
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if typ.ptrdata == 0 {
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return
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}
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if !cgoIsGoPointer(src) {
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return
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}
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if cgoIsGoPointer(dst) {
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return
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}
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p := src
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for i := 0; i < n; i++ {
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cgoCheckTypedBlock(typ, p, 0, typ.size)
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p = add(p, typ.size)
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}
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}
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// cgoCheckTypedBlock checks the block of memory at src, for up to size bytes,
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// and throws if it finds a Go pointer. The type of the memory is typ,
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// and src is off bytes into that type.
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//go:nosplit
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//go:nowritebarrier
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func cgoCheckTypedBlock(typ *_type, src unsafe.Pointer, off, size uintptr) {
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// Anything past typ.ptrdata is not a pointer.
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if typ.ptrdata <= off {
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return
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}
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if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
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size = ptrdataSize
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}
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if typ.kind&kindGCProg == 0 {
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cgoCheckBits(src, typ.gcdata, off, size)
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return
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}
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// The type has a GC program. Try to find GC bits somewhere else.
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roots := gcRoots
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for roots != nil {
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for i := 0; i < roots.count; i++ {
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pr := roots.roots[i]
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addr := uintptr(pr.decl)
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if cgoInRange(src, addr, addr+pr.size) {
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doff := uintptr(src) - addr
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cgoCheckBits(add(src, -doff), pr.gcdata, off+doff, size)
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return
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}
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}
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roots = roots.next
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}
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s := spanOfUnchecked(uintptr(src))
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if s.state.get() == mSpanManual {
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// There are no heap bits for value stored on the stack.
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// For a channel receive src might be on the stack of some
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// other goroutine, so we can't unwind the stack even if
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// we wanted to.
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// We can't expand the GC program without extra storage
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// space we can't easily get.
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// Fortunately we have the type information.
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systemstack(func() {
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cgoCheckUsingType(typ, src, off, size)
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})
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return
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}
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// src must be in the regular heap.
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hbits := heapBitsForAddr(uintptr(src))
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for i := uintptr(0); i < off+size; i += goarch.PtrSize {
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bits := hbits.bits()
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if i >= off && bits&bitPointer != 0 {
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v := *(*unsafe.Pointer)(add(src, i))
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if cgoIsGoPointer(v) {
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throw(cgoWriteBarrierFail)
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}
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}
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hbits = hbits.next()
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}
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}
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// cgoCheckBits checks the block of memory at src, for up to size
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// bytes, and throws if it finds a Go pointer. The gcbits mark each
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// pointer value. The src pointer is off bytes into the gcbits.
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//go:nosplit
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//go:nowritebarrier
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func cgoCheckBits(src unsafe.Pointer, gcbits *byte, off, size uintptr) {
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skipMask := off / goarch.PtrSize / 8
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skipBytes := skipMask * goarch.PtrSize * 8
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ptrmask := addb(gcbits, skipMask)
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src = add(src, skipBytes)
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off -= skipBytes
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size += off
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var bits uint32
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for i := uintptr(0); i < size; i += goarch.PtrSize {
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if i&(goarch.PtrSize*8-1) == 0 {
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bits = uint32(*ptrmask)
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ptrmask = addb(ptrmask, 1)
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} else {
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bits >>= 1
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}
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if off > 0 {
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off -= goarch.PtrSize
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} else {
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if bits&1 != 0 {
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v := *(*unsafe.Pointer)(add(src, i))
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if cgoIsGoPointer(v) {
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throw(cgoWriteBarrierFail)
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}
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}
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}
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}
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}
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// cgoCheckUsingType is like cgoCheckTypedBlock, but is a last ditch
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// fall back to look for pointers in src using the type information.
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// We only use this when looking at a value on the stack when the type
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// uses a GC program, because otherwise it's more efficient to use the
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// GC bits. This is called on the system stack.
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//go:nowritebarrier
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//go:systemstack
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func cgoCheckUsingType(typ *_type, src unsafe.Pointer, off, size uintptr) {
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if typ.ptrdata == 0 {
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return
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}
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// Anything past typ.ptrdata is not a pointer.
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if typ.ptrdata <= off {
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return
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}
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if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
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size = ptrdataSize
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}
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if typ.kind&kindGCProg == 0 {
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cgoCheckBits(src, typ.gcdata, off, size)
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return
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}
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switch typ.kind & kindMask {
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default:
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throw("can't happen")
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case kindArray:
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at := (*arraytype)(unsafe.Pointer(typ))
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for i := uintptr(0); i < at.len; i++ {
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if off < at.elem.size {
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cgoCheckUsingType(at.elem, src, off, size)
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}
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src = add(src, at.elem.size)
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skipped := off
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if skipped > at.elem.size {
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skipped = at.elem.size
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}
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checked := at.elem.size - skipped
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off -= skipped
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if size <= checked {
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return
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}
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size -= checked
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}
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case kindStruct:
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st := (*structtype)(unsafe.Pointer(typ))
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for _, f := range st.fields {
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if off < f.typ.size {
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cgoCheckUsingType(f.typ, src, off, size)
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}
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src = add(src, f.typ.size)
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skipped := off
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if skipped > f.typ.size {
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skipped = f.typ.size
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}
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checked := f.typ.size - skipped
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off -= skipped
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if size <= checked {
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return
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}
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size -= checked
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}
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}
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}
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