libgo/go/runtime/checkptr.go

   1 // Copyright 2019 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 // +build ignore
   6
   7 package runtime
   8
   9 import "unsafe"
  10
  11 func checkptrAlignment(p unsafe.Pointer, elem *_type, n uintptr) {
  12         // Check that (*[n]elem)(p) is appropriately aligned.
  13         // Note that we allow unaligned pointers if the types they point to contain
  14         // no pointers themselves. See issue 37298.
  15         // TODO(mdempsky): What about fieldAlign?
  16         if elem.ptrdata != 0 && uintptr(p)&(uintptr(elem.align)-1) != 0 {
  17                 throw("checkptr: unsafe pointer conversion")
  18         }
  19
  20         // Check that (*[n]elem)(p) doesn't straddle multiple heap objects.
  21         if size := n * elem.size; size > 1 && checkptrBase(p) != checkptrBase(add(p, size-1)) {
  22                 throw("checkptr: unsafe pointer conversion")
  23         }
  24 }
  25
  26 func checkptrArithmetic(p unsafe.Pointer, originals []unsafe.Pointer) {
  27         if 0 < uintptr(p) && uintptr(p) < minLegalPointer {
  28                 throw("checkptr: unsafe pointer arithmetic")
  29         }
  30
  31         // Check that if the computed pointer p points into a heap
  32         // object, then one of the original pointers must have pointed
  33         // into the same object.
  34         base := checkptrBase(p)
  35         if base == 0 {
  36                 return
  37         }
  38
  39         for _, original := range originals {
  40                 if base == checkptrBase(original) {
  41                         return
  42                 }
  43         }
  44
  45         throw("checkptr: unsafe pointer arithmetic")
  46 }
  47
  48 // checkptrBase returns the base address for the allocation containing
  49 // the address p.
  50 //
  51 // Importantly, if p1 and p2 point into the same variable, then
  52 // checkptrBase(p1) == checkptrBase(p2). However, the converse/inverse
  53 // is not necessarily true as allocations can have trailing padding,
  54 // and multiple variables may be packed into a single allocation.
  55 func checkptrBase(p unsafe.Pointer) uintptr {
  56         // stack
  57         if gp := getg(); gp.stack.lo <= uintptr(p) && uintptr(p) < gp.stack.hi {
  58                 // TODO(mdempsky): Walk the stack to identify the
  59                 // specific stack frame or even stack object that p
  60                 // points into.
  61                 //
  62                 // In the mean time, use "1" as a pseudo-address to
  63                 // represent the stack. This is an invalid address on
  64                 // all platforms, so it's guaranteed to be distinct
  65                 // from any of the addresses we might return below.
  66                 return 1
  67         }
  68
  69         // heap (must check after stack because of #35068)
  70         if base, _, _ := findObject(uintptr(p), 0, 0); base != 0 {
  71                 return base
  72         }
  73
  74         // data or bss
  75         for _, datap := range activeModules() {
  76                 if datap.data <= uintptr(p) && uintptr(p) < datap.edata {
  77                         return datap.data
  78                 }
  79                 if datap.bss <= uintptr(p) && uintptr(p) < datap.ebss {
  80                         return datap.bss
  81                 }
  82         }
  83
  84         return 0
  85 }