1 files changed, 39 insertions, 33 deletions

diff --git a/libgo/go/runtime/mbitmap.go b/libgo/go/runtime/mbitmap.go
index 0eb19d6..72cd9f3 100644
--- a/libgo/go/runtime/mbitmap.go
+++ b/libgo/go/runtime/mbitmap.go
@@ -226,16 +226,25 @@ func (s *mspan) isFree(index uintptr) bool {
 	return *bytep&mask == 0
 }
 
-func (s *mspan) objIndex(p uintptr) uintptr {
-	byteOffset := p - s.base()
-	if byteOffset == 0 {
-		return 0
-	}
-	if s.baseMask != 0 {
-		// s.baseMask is non-0, elemsize is a power of two, so shift by s.divShift
-		return byteOffset >> s.divShift
+// divideByElemSize returns n/s.elemsize.
+// n must be within [0, s.npages*_PageSize),
+// or may be exactly s.npages*_PageSize
+// if s.elemsize is from sizeclasses.go.
+func (s *mspan) divideByElemSize(n uintptr) uintptr {
+	const doubleCheck = false
+
+	// See explanation in mksizeclasses.go's computeDivMagic.
+	q := uintptr((uint64(n) * uint64(s.divMul)) >> 32)
+
+	if doubleCheck && q != n/s.elemsize {
+		println(n, "/", s.elemsize, "should be", n/s.elemsize, "but got", q)
+		throw("bad magic division")
 	}
-	return uintptr(((uint64(byteOffset) >> s.divShift) * uint64(s.divMul)) >> s.divShift2)
+	return q
+}
+
+func (s *mspan) objIndex(p uintptr) uintptr {
+	return s.divideByElemSize(p - s.base())
 }
 
 func markBitsForAddr(p uintptr) markBits {
@@ -324,6 +333,10 @@ func heapBitsForAddr(addr uintptr) (h heapBits) {
 	return
 }
 
+// clobberdeadPtr is a special value that is used by the compiler to
+// clobber dead stack slots, when -clobberdead flag is set.
+const clobberdeadPtr = uintptr(0xdeaddead | 0xdeaddead<<((^uintptr(0)>>63)*32))
+
 // badPointer throws bad pointer in heap panic.
 func badPointer(s *mspan, p, refBase, refOff uintptr) {
 	// Typically this indicates an incorrect use
@@ -336,13 +349,16 @@ func badPointer(s *mspan, p, refBase, refOff uintptr) {
 	// in allocated spans.
 	printlock()
 	print("runtime: pointer ", hex(p))
-	state := s.state.get()
-	if state != mSpanInUse {
-		print(" to unallocated span")
-	} else {
-		print(" to unused region of span")
+	if s != nil {
+		state := s.state.get()
+		if state != mSpanInUse {
+			print(" to unallocated span")
+		} else {
+			print(" to unused region of span")
+		}
+		print(" span.base()=", hex(s.base()), " span.limit=", hex(s.limit), " span.state=", state)
 	}
-	print(" span.base()=", hex(s.base()), " span.limit=", hex(s.limit), " span.state=", state, "\n")
+	print("\n")
 	if refBase != 0 {
 		print("runtime: found in object at *(", hex(refBase), "+", hex(refOff), ")\n")
 		gcDumpObject("object", refBase, refOff)
@@ -373,6 +389,12 @@ func findObject(p, refBase, refOff uintptr, forStack bool) (base uintptr, s *msp
 	// If s is nil, the virtual address has never been part of the heap.
 	// This pointer may be to some mmap'd region, so we allow it.
 	if s == nil {
+		if GOARCH == "amd64" && p == clobberdeadPtr && debug.invalidptr != 0 {
+			// Crash if clobberdeadPtr is seen. Only on AMD64 for now, as
+			// it is the only platform where compiler's clobberdead mode is
+			// implemented. On AMD64 clobberdeadPtr cannot be a valid address.
+			badPointer(s, p, refBase, refOff)
+		}
 		return
 	}
 	// If p is a bad pointer, it may not be in s's bounds.
@@ -402,24 +424,8 @@ func findObject(p, refBase, refOff uintptr, forStack bool) (base uintptr, s *msp
 		}
 	}
 
-	// If this span holds object of a power of 2 size, just mask off the bits to
-	// the interior of the object. Otherwise use the size to get the base.
-	if s.baseMask != 0 {
-		// optimize for power of 2 sized objects.
-		base = s.base()
-		base = base + (p-base)&uintptr(s.baseMask)
-		objIndex = (base - s.base()) >> s.divShift
-		// base = p & s.baseMask is faster for small spans,
-		// but doesn't work for large spans.
-		// Overall, it's faster to use the more general computation above.
-	} else {
-		base = s.base()
-		if p-base >= s.elemsize {
-			// n := (p - base) / s.elemsize, using division by multiplication
-			objIndex = uintptr(p-base) >> s.divShift * uintptr(s.divMul) >> s.divShift2
-			base += objIndex * s.elemsize
-		}
-	}
+	objIndex = s.objIndex(p)
+	base = s.base() + objIndex*s.elemsize
 	return
 }