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runtime: hashmap: move overflow pointer to end of bucket

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Pointers to zero-sized values may end up pointing to the next
object in memory, and possibly off the end of a span.  This
can cause memory leaks and/or confuse the garbage collector.

By putting the overflow pointer at the end of the bucket, we
make sure that pointers to any zero-sized keys or values don't
accidentally point to the next object in memory.

fixes #9384

Change-Id: I5d434df176984cb0210b4d0195dd106d6eb28f73
Reviewed-on: https://go-review.googlesource.com/1869
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Keith Randall 2014-12-19 20:44:18 -08:00
parent aaa4bf3720
commit fbc56cf050
5 changed files with 57 additions and 42 deletions
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9
src/reflect/type.go
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@ -1646,10 +1646,6 @@ func bucketOf(ktyp, etyp *rtype) *rtype {
for i := 0; i < int(bucketSize*unsafe.Sizeof(uint8(0))/ptrsize); i++ {
gc.append(bitsScalar)
}
gc.append(bitsPointer) // overflow
if runtime.GOARCH == "amd64p32" {
gc.append(bitsScalar)
}
// keys
for i := 0; i < bucketSize; i++ {
gc.appendProg(ktyp)
@ -1658,6 +1654,11 @@ func bucketOf(ktyp, etyp *rtype) *rtype {
for i := 0; i < bucketSize; i++ {
gc.appendProg(etyp)
}
// overflow
gc.append(bitsPointer)
if runtime.GOARCH == "amd64p32" {
gc.append(bitsScalar)
}
b := new(rtype)
b.size = gc.size