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.
11 "runtime/internal/sys"
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.
21 func cgoCheckWriteBarrier(dst *uintptr, src uintptr) {
22 if !cgoIsGoPointer(unsafe.Pointer(src)) {
25 if cgoIsGoPointer(unsafe.Pointer(dst)) {
29 // If we are running on the system stack then dst might be an
30 // address on the stack, which is OK.
32 if g == g.m.g0 || g == g.m.gsignal {
36 // Allocating memory can write to various mfixalloc structs
37 // that look like they are non-Go memory.
38 if g.m.mallocing != 0 {
43 println("write of Go pointer", hex(src), "to non-Go memory", hex(uintptr(unsafe.Pointer(dst))))
44 throw(cgoWriteBarrierFail)
48 // cgoCheckMemmove is called when moving a block of memory.
49 // dst and src point off bytes into the value to copy.
50 // size is the number of bytes to copy.
51 // It throws if the program is copying a block that contains a Go pointer
52 // into non-Go memory.
55 func cgoCheckMemmove(typ *_type, dst, src unsafe.Pointer, off, size uintptr) {
56 if typ.kind&kindNoPointers != 0 {
59 if !cgoIsGoPointer(src) {
62 if cgoIsGoPointer(dst) {
65 cgoCheckTypedBlock(typ, src, off, size)
68 // cgoCheckSliceCopy is called when copying n elements of a slice from
69 // src to dst. typ is the element type of the slice.
70 // It throws if the program is copying slice elements that contain Go pointers
71 // into non-Go memory.
74 func cgoCheckSliceCopy(typ *_type, dst, src slice, n int) {
75 if typ.kind&kindNoPointers != 0 {
78 if !cgoIsGoPointer(src.array) {
81 if cgoIsGoPointer(dst.array) {
85 for i := 0; i < n; i++ {
86 cgoCheckTypedBlock(typ, p, 0, typ.size)
91 // cgoCheckTypedBlock checks the block of memory at src, for up to size bytes,
92 // and throws if it finds a Go pointer. The type of the memory is typ,
93 // and src is off bytes into that type.
96 func cgoCheckTypedBlock(typ *_type, src unsafe.Pointer, off, size uintptr) {
97 if typ.kind&kindGCProg == 0 {
98 cgoCheckBits(src, typ.gcdata, off, size)
102 // The type has a GC program. Try to find GC bits somewhere else.
103 for datap := &firstmoduledata; datap != nil; datap = datap.next {
104 if cgoInRange(src, datap.data, datap.edata) {
105 doff := uintptr(src) - datap.data
106 cgoCheckBits(add(src, -doff), datap.gcdatamask.bytedata, off+doff, size)
109 if cgoInRange(src, datap.bss, datap.ebss) {
110 boff := uintptr(src) - datap.bss
111 cgoCheckBits(add(src, -boff), datap.gcbssmask.bytedata, off+boff, size)
116 aoff := uintptr(src) - mheap_.arena_start
117 idx := aoff >> _PageShift
119 if s.state == _MSpanStack {
120 // There are no heap bits for value stored on the stack.
121 // For a channel receive src might be on the stack of some
122 // other goroutine, so we can't unwind the stack even if
124 // We can't expand the GC program without extra storage
125 // space we can't easily get.
126 // Fortunately we have the type information.
128 cgoCheckUsingType(typ, src, off, size)
133 // src must be in the regular heap.
135 hbits := heapBitsForAddr(uintptr(src))
136 for i := uintptr(0); i < off+size; i += sys.PtrSize {
138 if i >= off && bits&bitPointer != 0 {
139 v := *(*unsafe.Pointer)(add(src, i))
140 if cgoIsGoPointer(v) {
142 throw(cgoWriteBarrierFail)
150 // cgoCheckBits checks the block of memory at src, for up to size
151 // bytes, and throws if it finds a Go pointer. The gcbits mark each
152 // pointer value. The src pointer is off bytes into the gcbits.
155 func cgoCheckBits(src unsafe.Pointer, gcbits *byte, off, size uintptr) {
156 skipMask := off / sys.PtrSize / 8
157 skipBytes := skipMask * sys.PtrSize * 8
158 ptrmask := addb(gcbits, skipMask)
159 src = add(src, skipBytes)
163 for i := uintptr(0); i < size; i += sys.PtrSize {
164 if i&(sys.PtrSize*8-1) == 0 {
165 bits = uint32(*ptrmask)
166 ptrmask = addb(ptrmask, 1)
174 v := *(*unsafe.Pointer)(add(src, i))
175 if cgoIsGoPointer(v) {
177 throw(cgoWriteBarrierFail)
185 // cgoCheckUsingType is like cgoCheckTypedBlock, but is a last ditch
186 // fall back to look for pointers in src using the type information.
187 // We only this when looking at a value on the stack when the type
188 // uses a GC program, because otherwise it's more efficient to use the
189 // GC bits. This is called on the system stack.
192 func cgoCheckUsingType(typ *_type, src unsafe.Pointer, off, size uintptr) {
193 if typ.kind&kindNoPointers != 0 {
196 if typ.kind&kindGCProg == 0 {
197 cgoCheckBits(src, typ.gcdata, off, size)
200 switch typ.kind & kindMask {
202 throw("can't happen")
204 at := (*arraytype)(unsafe.Pointer(typ))
205 for i := uintptr(0); i < at.len; i++ {
206 if off < at.elem.size {
207 cgoCheckUsingType(at.elem, src, off, size)
209 src = add(src, at.elem.size)
211 if skipped > at.elem.size {
212 skipped = at.elem.size
214 checked := at.elem.size - skipped
222 st := (*structtype)(unsafe.Pointer(typ))
223 for _, f := range st.fields {
224 if off < f.typ.size {
225 cgoCheckUsingType(f.typ, src, off, size)
227 src = add(src, f.typ.size)
229 if skipped > f.typ.size {
232 checked := f.typ.size - skipped