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 aoff := uintptr(src) - mheap_.arena_start
129 idx := aoff >> _PageShift
130 s := mheap_.spans[idx]
131 if s.state == _MSpanManual {
132 // There are no heap bits for value stored on the stack.
133 // For a channel receive src might be on the stack of some
134 // other goroutine, so we can't unwind the stack even if
136 // We can't expand the GC program without extra storage
137 // space we can't easily get.
138 // Fortunately we have the type information.
140 cgoCheckUsingType(typ, src, off, size)
145 // src must be in the regular heap.
147 hbits := heapBitsForAddr(uintptr(src))
148 for i := uintptr(0); i < off+size; i += sys.PtrSize {
150 if i >= off && bits&bitPointer != 0 {
151 v := *(*unsafe.Pointer)(add(src, i))
152 if cgoIsGoPointer(v) {
154 throw(cgoWriteBarrierFail)
162 // cgoCheckBits checks the block of memory at src, for up to size
163 // bytes, and throws if it finds a Go pointer. The gcbits mark each
164 // pointer value. The src pointer is off bytes into the gcbits.
167 func cgoCheckBits(src unsafe.Pointer, gcbits *byte, off, size uintptr) {
168 skipMask := off / sys.PtrSize / 8
169 skipBytes := skipMask * sys.PtrSize * 8
170 ptrmask := addb(gcbits, skipMask)
171 src = add(src, skipBytes)
175 for i := uintptr(0); i < size; i += sys.PtrSize {
176 if i&(sys.PtrSize*8-1) == 0 {
177 bits = uint32(*ptrmask)
178 ptrmask = addb(ptrmask, 1)
186 v := *(*unsafe.Pointer)(add(src, i))
187 if cgoIsGoPointer(v) {
189 throw(cgoWriteBarrierFail)
197 // cgoCheckUsingType is like cgoCheckTypedBlock, but is a last ditch
198 // fall back to look for pointers in src using the type information.
199 // We only use this when looking at a value on the stack when the type
200 // uses a GC program, because otherwise it's more efficient to use the
201 // GC bits. This is called on the system stack.
204 func cgoCheckUsingType(typ *_type, src unsafe.Pointer, off, size uintptr) {
205 if typ.kind&kindNoPointers != 0 {
209 // Anything past typ.ptrdata is not a pointer.
210 if typ.ptrdata <= off {
213 if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
217 if typ.kind&kindGCProg == 0 {
218 cgoCheckBits(src, typ.gcdata, off, size)
221 switch typ.kind & kindMask {
223 throw("can't happen")
225 at := (*arraytype)(unsafe.Pointer(typ))
226 for i := uintptr(0); i < at.len; i++ {
227 if off < at.elem.size {
228 cgoCheckUsingType(at.elem, src, off, size)
230 src = add(src, at.elem.size)
232 if skipped > at.elem.size {
233 skipped = at.elem.size
235 checked := at.elem.size - skipped
243 st := (*structtype)(unsafe.Pointer(typ))
244 for _, f := range st.fields {
245 if off < f.typ.size {
246 cgoCheckUsingType(f.typ, src, off, size)
248 src = add(src, f.typ.size)
250 if skipped > f.typ.size {
253 checked := f.typ.size - skipped