libgo/go/runtime/cgocheck.go

   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.
   4
   5 // Code to check that pointer writes follow the cgo rules.
   6 // These functions are invoked via the write barrier when debug.cgocheck > 1.
   7
   8 package runtime
   9
  10 import (
  11         "runtime/internal/sys"
  12         "unsafe"
  13 )
  14
  15 const cgoWriteBarrierFail = "Go pointer stored into non-Go memory"
  16
  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.
  19 //go:nosplit
  20 //go:nowritebarrier
  21 func cgoCheckWriteBarrier(dst *uintptr, src uintptr) {
  22         if !cgoIsGoPointer(unsafe.Pointer(src)) {
  23                 return
  24         }
  25         if cgoIsGoPointer(unsafe.Pointer(dst)) {
  26                 return
  27         }
  28
  29         // If we are running on the system stack then dst might be an
  30         // address on the stack, which is OK.
  31         g := getg()
  32         if g == g.m.g0 || g == g.m.gsignal {
  33                 return
  34         }
  35
  36         // Allocating memory can write to various mfixalloc structs
  37         // that look like they are non-Go memory.
  38         if g.m.mallocing != 0 {
  39                 return
  40         }
  41
  42         systemstack(func() {
  43                 println("write of Go pointer", hex(src), "to non-Go memory", hex(uintptr(unsafe.Pointer(dst))))
  44                 throw(cgoWriteBarrierFail)
  45         })
  46 }
  47
  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.
  53 //go:nosplit
  54 //go:nowritebarrier
  55 func cgoCheckMemmove(typ *_type, dst, src unsafe.Pointer, off, size uintptr) {
  56         if typ.kind&kindNoPointers != 0 {
  57                 return
  58         }
  59         if !cgoIsGoPointer(src) {
  60                 return
  61         }
  62         if cgoIsGoPointer(dst) {
  63                 return
  64         }
  65         cgoCheckTypedBlock(typ, src, off, size)
  66 }
  67
  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.
  72 //go:nosplit
  73 //go:nowritebarrier
  74 func cgoCheckSliceCopy(typ *_type, dst, src slice, n int) {
  75         if typ.kind&kindNoPointers != 0 {
  76                 return
  77         }
  78         if !cgoIsGoPointer(src.array) {
  79                 return
  80         }
  81         if cgoIsGoPointer(dst.array) {
  82                 return
  83         }
  84         p := src.array
  85         for i := 0; i < n; i++ {
  86                 cgoCheckTypedBlock(typ, p, 0, typ.size)
  87                 p = add(p, typ.size)
  88         }
  89 }
  90
  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.
  94 //go:nosplit
  95 //go:nowritebarrier
  96 func cgoCheckTypedBlock(typ *_type, src unsafe.Pointer, off, size uintptr) {
  97         // Anything past typ.ptrdata is not a pointer.
  98         if typ.ptrdata <= off {
  99                 return
 100         }
 101         if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
 102                 size = ptrdataSize
 103         }
 104
 105         if typ.kind&kindGCProg == 0 {
 106                 cgoCheckBits(src, typ.gcdata, off, size)
 107                 return
 108         }
 109
 110         // The type has a GC program. Try to find GC bits somewhere else.
 111         for datap := &firstmoduledata; datap != nil; datap = datap.next {
 112                 if cgoInRange(src, datap.data, datap.edata) {
 113                         doff := uintptr(src) - datap.data
 114                         cgoCheckBits(add(src, -doff), datap.gcdatamask.bytedata, off+doff, size)
 115                         return
 116                 }
 117                 if cgoInRange(src, datap.bss, datap.ebss) {
 118                         boff := uintptr(src) - datap.bss
 119                         cgoCheckBits(add(src, -boff), datap.gcbssmask.bytedata, off+boff, size)
 120                         return
 121                 }
 122         }
 123
 124         aoff := uintptr(src) - mheap_.arena_start
 125         idx := aoff >> _PageShift
 126         s := h_spans[idx]
 127         if s.state == _MSpanStack {
 128                 // There are no heap bits for value stored on the stack.
 129                 // For a channel receive src might be on the stack of some
 130                 // other goroutine, so we can't unwind the stack even if
 131                 // we wanted to.
 132                 // We can't expand the GC program without extra storage
 133                 // space we can't easily get.
 134                 // Fortunately we have the type information.
 135                 systemstack(func() {
 136                         cgoCheckUsingType(typ, src, off, size)
 137                 })
 138                 return
 139         }
 140
 141         // src must be in the regular heap.
 142
 143         hbits := heapBitsForAddr(uintptr(src))
 144         for i := uintptr(0); i < off+size; i += sys.PtrSize {
 145                 bits := hbits.bits()
 146                 if i >= off && bits&bitPointer != 0 {
 147                         v := *(*unsafe.Pointer)(add(src, i))
 148                         if cgoIsGoPointer(v) {
 149                                 systemstack(func() {
 150                                         throw(cgoWriteBarrierFail)
 151                                 })
 152                         }
 153                 }
 154                 hbits = hbits.next()
 155         }
 156 }
 157
 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.
 161 //go:nosplit
 162 //go:nowritebarrier
 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)
 168         off -= skipBytes
 169         size += off
 170         var bits uint32
 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)
 175                 } else {
 176                         bits >>= 1
 177                 }
 178                 if off > 0 {
 179                         off -= sys.PtrSize
 180                 } else {
 181                         if bits&1 != 0 {
 182                                 v := *(*unsafe.Pointer)(add(src, i))
 183                                 if cgoIsGoPointer(v) {
 184                                         systemstack(func() {
 185                                                 throw(cgoWriteBarrierFail)
 186                                         })
 187                                 }
 188                         }
 189                 }
 190         }
 191 }
 192
 193 // cgoCheckUsingType is like cgoCheckTypedBlock, but is a last ditch
 194 // fall back to look for pointers in src using the type information.
 195 // We only use this when looking at a value on the stack when the type
 196 // uses a GC program, because otherwise it's more efficient to use the
 197 // GC bits. This is called on the system stack.
 198 //go:nowritebarrier
 199 //go:systemstack
 200 func cgoCheckUsingType(typ *_type, src unsafe.Pointer, off, size uintptr) {
 201         if typ.kind&kindNoPointers != 0 {
 202                 return
 203         }
 204
 205         // Anything past typ.ptrdata is not a pointer.
 206         if typ.ptrdata <= off {
 207                 return
 208         }
 209         if ptrdataSize := typ.ptrdata - off; size > ptrdataSize {
 210                 size = ptrdataSize
 211         }
 212
 213         if typ.kind&kindGCProg == 0 {
 214                 cgoCheckBits(src, typ.gcdata, off, size)
 215                 return
 216         }
 217         switch typ.kind & kindMask {
 218         default:
 219                 throw("can't happen")
 220         case kindArray:
 221                 at := (*arraytype)(unsafe.Pointer(typ))
 222                 for i := uintptr(0); i < at.len; i++ {
 223                         if off < at.elem.size {
 224                                 cgoCheckUsingType(at.elem, src, off, size)
 225                         }
 226                         src = add(src, at.elem.size)
 227                         skipped := off
 228                         if skipped > at.elem.size {
 229                                 skipped = at.elem.size
 230                         }
 231                         checked := at.elem.size - skipped
 232                         off -= skipped
 233                         if size <= checked {
 234                                 return
 235                         }
 236                         size -= checked
 237                 }
 238         case kindStruct:
 239                 st := (*structtype)(unsafe.Pointer(typ))
 240                 for _, f := range st.fields {
 241                         if off < f.typ.size {
 242                                 cgoCheckUsingType(f.typ, src, off, size)
 243                         }
 244                         src = add(src, f.typ.size)
 245                         skipped := off
 246                         if skipped > f.typ.size {
 247                                 skipped = f.typ.size
 248                         }
 249                         checked := f.typ.size - skipped
 250                         off -= skipped
 251                         if size <= checked {
 252                                 return
 253                         }
 254                         size -= checked
 255                 }
 256         }
 257 }