1 // Copyright 2015 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Code to check that pointer writes follow the cgo rules.
6 // These functions are invoked via the write barrier when debug.cgocheck > 1.
15 const cgoWriteBarrierFail = "Go pointer stored into non-Go memory"
17 // cgoCheckWriteBarrier is called whenever a pointer is stored into memory.
18 // It throws if the program is storing a Go pointer into non-Go memory.
20 // This is called from the write barrier, so its entire call tree must
25 func cgoCheckWriteBarrier(dst *uintptr, src uintptr) {
26 if !cgoIsGoPointer(unsafe.Pointer(src)) {
29 if cgoIsGoPointer(unsafe.Pointer(dst)) {
33 // If we are running on the system stack then dst might be an
34 // address on the stack, which is OK.
36 if gp == gp.m.g0 || gp == gp.m.gsignal {
40 // Allocating memory can write to various mfixalloc structs
41 // that look like they are non-Go memory.
42 if gp.m.mallocing != 0 {
46 // It's OK if writing to memory allocated by persistentalloc.
47 // Do this check last because it is more expensive and rarely true.
48 // If it is false the expense doesn't matter since we are crashing.
49 if inPersistentAlloc(uintptr(unsafe.Pointer(dst))) {
54 println("write of Go pointer", hex(src), "to non-Go memory", hex(uintptr(unsafe.Pointer(dst))))
55 throw(cgoWriteBarrierFail)
59 // cgoCheckMemmove is called when moving a block of memory.
60 // dst and src point off bytes into the value to copy.
61 // size is the number of bytes to copy.
62 // It throws if the program is copying a block that contains a Go pointer
63 // into non-Go memory.
67 func cgoCheckMemmove(typ *_type, dst, src unsafe.Pointer, off, size uintptr) {
71 if !cgoIsGoPointer(src) {
74 if cgoIsGoPointer(dst) {
77 cgoCheckTypedBlock(typ, src, off, size)
80 // cgoCheckSliceCopy is called when copying n elements of a slice.
81 // src and dst are pointers to the first element of the slice.
82 // typ is the element type of the slice.
83 // It throws if the program is copying slice elements that contain Go pointers
84 // into non-Go memory.
88 func cgoCheckSliceCopy(typ *_type, dst, src unsafe.Pointer, n int) {
92 if !cgoIsGoPointer(src) {
95 if cgoIsGoPointer(dst) {
99 for i := 0; i < n; i++ {
100 cgoCheckTypedBlock(typ, p, 0, typ.size)
105 // cgoCheckTypedBlock checks the block of memory at src, for up to size bytes,
106 // and throws if it finds a Go pointer. The type of the memory is typ,
107 // and src is off bytes into that type.
111 func cgoCheckTypedBlock(typ *_type, src unsafe.Pointer, off, size uintptr) {
112 // Anything past typ.ptrdata is not a pointer.
113 if typ.ptrdata <= off {
116 if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
120 if typ.kind&kindGCProg == 0 {
121 cgoCheckBits(src, typ.gcdata, off, size)
125 // The type has a GC program. Try to find GC bits somewhere else.
126 for _, datap := range activeModules() {
127 if cgoInRange(src, datap.data, datap.edata) {
128 doff := uintptr(src) - datap.data
129 cgoCheckBits(add(src, -doff), datap.gcdatamask.bytedata, off+doff, size)
132 if cgoInRange(src, datap.bss, datap.ebss) {
133 boff := uintptr(src) - datap.bss
134 cgoCheckBits(add(src, -boff), datap.gcbssmask.bytedata, off+boff, size)
139 s := spanOfUnchecked(uintptr(src))
140 if s.state.get() == mSpanManual {
141 // There are no heap bits for value stored on the stack.
142 // For a channel receive src might be on the stack of some
143 // other goroutine, so we can't unwind the stack even if
145 // We can't expand the GC program without extra storage
146 // space we can't easily get.
147 // Fortunately we have the type information.
149 cgoCheckUsingType(typ, src, off, size)
154 // src must be in the regular heap.
156 hbits := heapBitsForAddr(uintptr(src))
157 for i := uintptr(0); i < off+size; i += goarch.PtrSize {
159 if i >= off && bits&bitPointer != 0 {
160 v := *(*unsafe.Pointer)(add(src, i))
161 if cgoIsGoPointer(v) {
162 throw(cgoWriteBarrierFail)
169 // cgoCheckBits checks the block of memory at src, for up to size
170 // bytes, and throws if it finds a Go pointer. The gcbits mark each
171 // pointer value. The src pointer is off bytes into the gcbits.
175 func cgoCheckBits(src unsafe.Pointer, gcbits *byte, off, size uintptr) {
176 skipMask := off / goarch.PtrSize / 8
177 skipBytes := skipMask * goarch.PtrSize * 8
178 ptrmask := addb(gcbits, skipMask)
179 src = add(src, skipBytes)
183 for i := uintptr(0); i < size; i += goarch.PtrSize {
184 if i&(goarch.PtrSize*8-1) == 0 {
185 bits = uint32(*ptrmask)
186 ptrmask = addb(ptrmask, 1)
191 off -= goarch.PtrSize
194 v := *(*unsafe.Pointer)(add(src, i))
195 if cgoIsGoPointer(v) {
196 throw(cgoWriteBarrierFail)
203 // cgoCheckUsingType is like cgoCheckTypedBlock, but is a last ditch
204 // fall back to look for pointers in src using the type information.
205 // We only use this when looking at a value on the stack when the type
206 // uses a GC program, because otherwise it's more efficient to use the
207 // GC bits. This is called on the system stack.
211 func cgoCheckUsingType(typ *_type, src unsafe.Pointer, off, size uintptr) {
212 if typ.ptrdata == 0 {
216 // Anything past typ.ptrdata is not a pointer.
217 if typ.ptrdata <= off {
220 if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
224 if typ.kind&kindGCProg == 0 {
225 cgoCheckBits(src, typ.gcdata, off, size)
228 switch typ.kind & kindMask {
230 throw("can't happen")
232 at := (*arraytype)(unsafe.Pointer(typ))
233 for i := uintptr(0); i < at.len; i++ {
234 if off < at.elem.size {
235 cgoCheckUsingType(at.elem, src, off, size)
237 src = add(src, at.elem.size)
239 if skipped > at.elem.size {
240 skipped = at.elem.size
242 checked := at.elem.size - skipped
250 st := (*structtype)(unsafe.Pointer(typ))
251 for _, f := range st.fields {
252 if off < f.typ.size {
253 cgoCheckUsingType(f.typ, src, off, size)
255 src = add(src, f.typ.size)
257 if skipped > f.typ.size {
260 checked := f.typ.size - skipped