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.
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 g == g.m.g0 || g == g.m.gsignal {
40 // Allocating memory can write to various mfixalloc structs
41 // that look like they are non-Go memory.
42 if g.m.mallocing != 0 {
47 println("write of Go pointer", hex(src), "to non-Go memory", hex(uintptr(unsafe.Pointer(dst))))
48 throw(cgoWriteBarrierFail)
52 // cgoCheckMemmove is called when moving a block of memory.
53 // dst and src point off bytes into the value to copy.
54 // size is the number of bytes to copy.
55 // It throws if the program is copying a block that contains a Go pointer
56 // into non-Go memory.
59 func cgoCheckMemmove(typ *_type, dst, src unsafe.Pointer, off, size uintptr) {
60 if typ.kind&kindNoPointers != 0 {
63 if !cgoIsGoPointer(src) {
66 if cgoIsGoPointer(dst) {
69 cgoCheckTypedBlock(typ, src, off, size)
72 // cgoCheckSliceCopy is called when copying n elements of a slice from
73 // src to dst. typ is the element type of the slice.
74 // It throws if the program is copying slice elements that contain Go pointers
75 // into non-Go memory.
78 func cgoCheckSliceCopy(typ *_type, dst, src slice, n int) {
79 if typ.kind&kindNoPointers != 0 {
82 if !cgoIsGoPointer(src.array) {
85 if cgoIsGoPointer(dst.array) {
89 for i := 0; i < n; i++ {
90 cgoCheckTypedBlock(typ, p, 0, typ.size)
95 // cgoCheckTypedBlock checks the block of memory at src, for up to size bytes,
96 // and throws if it finds a Go pointer. The type of the memory is typ,
97 // and src is off bytes into that type.
100 func cgoCheckTypedBlock(typ *_type, src unsafe.Pointer, off, size uintptr) {
101 // Anything past typ.ptrdata is not a pointer.
102 if typ.ptrdata <= off {
105 if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
109 if typ.kind&kindGCProg == 0 {
110 cgoCheckBits(src, typ.gcdata, off, size)
114 // The type has a GC program. Try to find GC bits somewhere else.
115 for _, datap := range activeModules() {
116 if cgoInRange(src, datap.data, datap.edata) {
117 doff := uintptr(src) - datap.data
118 cgoCheckBits(add(src, -doff), datap.gcdatamask.bytedata, off+doff, size)
121 if cgoInRange(src, datap.bss, datap.ebss) {
122 boff := uintptr(src) - datap.bss
123 cgoCheckBits(add(src, -boff), datap.gcbssmask.bytedata, off+boff, size)
128 s := spanOfUnchecked(uintptr(src))
129 if s.state == _MSpanManual {
130 // There are no heap bits for value stored on the stack.
131 // For a channel receive src might be on the stack of some
132 // other goroutine, so we can't unwind the stack even if
134 // We can't expand the GC program without extra storage
135 // space we can't easily get.
136 // Fortunately we have the type information.
138 cgoCheckUsingType(typ, src, off, size)
143 // src must be in the regular heap.
145 hbits := heapBitsForAddr(uintptr(src))
146 for i := uintptr(0); i < off+size; i += sys.PtrSize {
148 if i >= off && bits&bitPointer != 0 {
149 v := *(*unsafe.Pointer)(add(src, i))
150 if cgoIsGoPointer(v) {
151 throw(cgoWriteBarrierFail)
158 // cgoCheckBits checks the block of memory at src, for up to size
159 // bytes, and throws if it finds a Go pointer. The gcbits mark each
160 // pointer value. The src pointer is off bytes into the gcbits.
163 func cgoCheckBits(src unsafe.Pointer, gcbits *byte, off, size uintptr) {
164 skipMask := off / sys.PtrSize / 8
165 skipBytes := skipMask * sys.PtrSize * 8
166 ptrmask := addb(gcbits, skipMask)
167 src = add(src, skipBytes)
171 for i := uintptr(0); i < size; i += sys.PtrSize {
172 if i&(sys.PtrSize*8-1) == 0 {
173 bits = uint32(*ptrmask)
174 ptrmask = addb(ptrmask, 1)
182 v := *(*unsafe.Pointer)(add(src, i))
183 if cgoIsGoPointer(v) {
184 throw(cgoWriteBarrierFail)
191 // cgoCheckUsingType is like cgoCheckTypedBlock, but is a last ditch
192 // fall back to look for pointers in src using the type information.
193 // We only use this when looking at a value on the stack when the type
194 // uses a GC program, because otherwise it's more efficient to use the
195 // GC bits. This is called on the system stack.
198 func cgoCheckUsingType(typ *_type, src unsafe.Pointer, off, size uintptr) {
199 if typ.kind&kindNoPointers != 0 {
203 // Anything past typ.ptrdata is not a pointer.
204 if typ.ptrdata <= off {
207 if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
211 if typ.kind&kindGCProg == 0 {
212 cgoCheckBits(src, typ.gcdata, off, size)
215 switch typ.kind & kindMask {
217 throw("can't happen")
219 at := (*arraytype)(unsafe.Pointer(typ))
220 for i := uintptr(0); i < at.len; i++ {
221 if off < at.elem.size {
222 cgoCheckUsingType(at.elem, src, off, size)
224 src = add(src, at.elem.size)
226 if skipped > at.elem.size {
227 skipped = at.elem.size
229 checked := at.elem.size - skipped
237 st := (*structtype)(unsafe.Pointer(typ))
238 for _, f := range st.fields {
239 if off < f.typ.size {
240 cgoCheckUsingType(f.typ, src, off, size)
242 src = add(src, f.typ.size)
244 if skipped > f.typ.size {
247 checked := f.typ.size - skipped