diff --git a/lib/system/gc_stack.nim b/lib/system/gc_stack.nim
new file mode 100644
index 000000000..3a5c5594a
--- /dev/null
+++ b/lib/system/gc_stack.nim
@@ -0,0 +1,382 @@
+#
+#            Nim's Runtime Library
+#        (c) Copyright 2016 Andreas Rumpf
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+# "Stack GC" for embedded devices or ultra performance requirements.
+
+include osalloc
+
+# We manage memory as a thread local stack. Since the allocation pointer
+# is detached from the control flow pointer, this model is vastly more
+# useful than the traditional programming model while almost as safe.
+# Individual objects can also be deleted but no coalescing is performed.
+# Stacks can also be moved from one thread to another.
+
+# We also support 'finalizers'.
+
+type
+  Finalizer {.compilerproc.} = proc (self: pointer) {.nimcall, benign.}
+    # A ref type can have a finalizer that is called before the object's
+    # storage is freed.
+
+  AlignType = BiggestFloat
+  ObjHeader = object
+    typ: PNimType
+    nextFinal: ptr ObjHeader # next object with finalizer
+
+  Hole = object # stacks can have holes. Otherwise 'growObj' would be insane.
+    zeroTyp: pointer # overlaid with 'typ' field. Always 'nil'.
+    size: int # size of the free slot
+
+  Chunk = ptr BaseChunk
+  BaseChunk = object
+    next: Chunk
+    size: int
+    head, last: ptr ObjHeader # first and last object in chunk that
+                              # has a finalizer attached to it
+
+type
+  StackPtr = object
+    chunk: pointer
+    remaining: int
+    current: Chunk
+
+  MemRegion* = object
+    remaining: int
+    chunk: pointer
+    head, last: Chunk
+    nextChunkSize, totalSize: int
+    hole: ptr Hole # we support individual freeing
+    lock: SysLock
+
+var
+  region {.threadVar.}: MemRegion
+
+template withRegion*(r: MemRegion; body: untyped) =
+  let oldRegion = region
+  region = r
+  try:
+    body
+  finally:
+    region = oldRegion
+
+template inc(p: pointer, s: int) =
+  p = cast[pointer](cast[int](p) +% s)
+
+template `+!`(p: pointer, s: int): pointer =
+  cast[pointer](cast[int](p) +% s)
+
+template `-!`(p: pointer, s: int): pointer =
+  cast[pointer](cast[int](p) +% s)
+
+proc allocSlowPath(r: var MemRegion; size: int) =
+  # we need to ensure that the underlying linked list
+  # stays small. Say we want to grab 16GB of RAM with some
+  # exponential growth function. So we allocate 16KB, then
+  # 32 KB, 64 KB, 128KB, 256KB, 512KB, 1MB, 2MB, 4MB,
+  # 8MB, 16MB, 32MB, 64MB, 128MB, 512MB, 1GB, 2GB, 4GB, 8GB,
+  # 16GB --> list contains only 20 elements! That's reasonable.
+  if (r.totalSize and 1) == 0:
+    r.nextChunkSize =
+      if r.totalSize < 64 * 1024: PageSize*4
+      else: r.nextChunkSize*2
+  var s = align(size+sizeof(BaseChunk), PageSize)
+  var fresh: Chunk
+  if s > r.nextChunkSize:
+    fresh = cast[Chunk](osAllocPages(s))
+  else:
+    fresh = cast[Chunk](osTryAllocPages(r.nextChunkSize))
+    if fresh == nil:
+      fresh = cast[Chunk](osAllocPages(s))
+      # lowest bit in totalSize is the "don't increase nextChunkSize"
+      inc r.totalSize
+    else:
+      s = r.nextChunkSize
+  fresh.size = s
+  fresh.final = nil
+  r.totalSize += s
+  let old = r.last
+  if old == nil:
+    r.head = fresh
+  else:
+    r.last.next = fresh
+  r.chunk = fresh +! sizeof(BaseChunk)
+  r.last = fresh
+  r.remaining = s - sizeof(BaseChunk)
+
+proc alloc(r: var MemRegion; size: int): pointer {.inline.} =
+  if unlikely(r.remaining < size): allocSlowPath(r, size)
+  dec(r.remaining, size)
+  result = r.chunk
+  inc r.chunk, size
+
+proc runFinalizers(c: Chunk) =
+  var it = c.head
+  while it != nil:
+    # indivually freed objects with finalizer stay in the list, but
+    # their typ is nil then:
+    if it.typ != nil and it.typ.finalizer != nil:
+      (cast[Finalizer](cell.typ.finalizer))(cell+!sizeof(ObjHeader))
+    it = it.next
+
+proc dealloc(r: var MemRegion; p: pointer) =
+  let it = p-!sizeof(ObjHeader)
+  if it.typ != nil and it.typ.finalizer != nil:
+    (cast[Finalizer](cell.typ.finalizer))(p)
+  it.typ = nil
+
+proc deallocAll(head: Chunk) =
+  var it = head
+  while it != nil:
+    runFinalizers(it)
+    osDeallocPages(it, it.size)
+    it = it.next
+
+proc deallocAll*(r: var MemRegion) =
+  deallocAll(r.head)
+  zeroMem(addr r, sizeof r)
+
+proc obstackPtr*(r: MemRegion): StackPtr =
+  result.chunk = r.chunk
+  result.remaining = r.remaining
+  result.current = r.last
+
+proc setObstackPtr*(r: MemRegion; sp: StackPtr) =
+  # free everything after 'sp':
+  if sp.current != nil:
+    deallocAll(sp.current.next)
+  r.chunk = sp.chunk
+  r.remaining = sp.remaining
+  r.last = sp.current
+
+proc joinRegion*(dest: var MemRegion; src: MemRegion) =
+  # merging is not hard.
+  if dest.head.isNil:
+    dest.head = src.head
+  else:
+    dest.last.next = src.head
+  dest.last = src.last
+  dest.chunk = src.chunk
+  dest.remaining = src.remaining
+  dest.nextChunkSize = max(dest.nextChunkSize, src.nextChunkSize)
+  dest.totalSize += src.totalSize
+  if dest.hole.size < src.hole.size:
+    dest.hole = src.hole
+
+proc isOnHeap*(r: MemRegion; p: pointer): bool =
+  # the last chunk is the largest, so check it first. It's also special
+  # in that contains the current bump pointer:
+  if r.last >= p and p < r.chunk:
+    return true
+  var it = r.head
+  while it != r.last:
+    if it >= p and p <= it+!it.size: return true
+    it = it.next
+
+proc isInteriorPointer(r: MemRegion; p: pointer): pointer =
+  discard " we cannot patch stack pointers anyway!"
+
+type
+  PointerStackChunk = object
+    next, prev: ptr PointerStackChunk
+    len: int
+    data: array[128, pointer]
+
+template head(s: PointerStackChunk): untyped = s.prev
+template tail(s: PointerStackChunk): untyped = s.next
+
+include chains
+
+proc push(r: var MemRegion; s: var PointerStackChunk; x: pointer) =
+  if s.len < high(s.data):
+    s.data[s.len] = x
+    inc s.len
+  else:
+    let fresh = cast[ptr PointerStackChunk](alloc(r, sizeof(PointerStackChunk)))
+    fresh.len = 1
+    fresh.data[0] = x
+    fresh.next = nil
+    fresh.prev = nil
+    append(s, fresh)
+
+
+proc genericDeepCopyAux(dr: var MemRegion; stack: var PointerStackChunk;
+                        dest, src: pointer, mt: PNimType) {.benign.}
+proc genericDeepCopyAux(dr: var MemRegion; stack: var PointerStackChunk;
+                        dest, src: pointer, n: ptr TNimNode) {.benign.} =
+  var
+    d = cast[ByteAddress](dest)
+    s = cast[ByteAddress](src)
+  case n.kind
+  of nkSlot:
+    genericDeepCopyAux(cast[pointer](d +% n.offset),
+                       cast[pointer](s +% n.offset), n.typ)
+  of nkList:
+    for i in 0..n.len-1:
+      genericDeepCopyAux(dest, src, n.sons[i])
+  of nkCase:
+    var dd = selectBranch(dest, n)
+    var m = selectBranch(src, n)
+    # reset if different branches are in use; note different branches also
+    # imply that's not self-assignment (``x = x``)!
+    if m != dd and dd != nil:
+      genericResetAux(dest, dd)
+    copyMem(cast[pointer](d +% n.offset), cast[pointer](s +% n.offset),
+            n.typ.size)
+    if m != nil:
+      genericDeepCopyAux(dest, src, m)
+  of nkNone: sysAssert(false, "genericDeepCopyAux")
+
+proc copyDeepString(dr: var MemRegion; stack: var PointerStackChunk; src: NimString): NimString {.inline.} =
+  result = rawNewStringNoInit(dr, src.len)
+  result.len = src.len
+  c_memcpy(result.data, src.data, src.len + 1)
+
+proc genericDeepCopyAux(dr: var MemRegion; stack: var PointerStackChunk;
+                        dest, src: pointer, mt: PNimType) =
+  var
+    d = cast[ByteAddress](dest)
+    s = cast[ByteAddress](src)
+  sysAssert(mt != nil, "genericDeepCopyAux 2")
+  case mt.kind
+  of tyString:
+    var x = cast[PPointer](dest)
+    var s2 = cast[PPointer](s)[]
+    if s2 == nil:
+      x[] = nil
+    else:
+      x[] = copyDeepString(cast[NimString](s2))
+  of tySequence:
+    var s2 = cast[PPointer](src)[]
+    var seq = cast[PGenericSeq](s2)
+    var x = cast[PPointer](dest)
+    if s2 == nil:
+      x[] = nil
+      return
+    sysAssert(dest != nil, "genericDeepCopyAux 3")
+    x[] = newSeq(mt, seq.len)
+    var dst = cast[ByteAddress](cast[PPointer](dest)[])
+    for i in 0..seq.len-1:
+      genericDeepCopyAux(dr, stack,
+        cast[pointer](dst +% i*% mt.base.size +% GenericSeqSize),
+        cast[pointer](cast[ByteAddress](s2) +% i *% mt.base.size +%
+                     GenericSeqSize),
+        mt.base)
+  of tyObject:
+    # we need to copy m_type field for tyObject, as it could be empty for
+    # sequence reallocations:
+    var pint = cast[ptr PNimType](dest)
+    pint[] = cast[ptr PNimType](src)[]
+    if mt.base != nil:
+      genericDeepCopyAux(dr, stack, dest, src, mt.base)
+    genericDeepCopyAux(dr, stack, dest, src, mt.node)
+  of tyTuple:
+    genericDeepCopyAux(dr, stack, dest, src, mt.node)
+  of tyArray, tyArrayConstr:
+    for i in 0..(mt.size div mt.base.size)-1:
+      genericDeepCopyAux(dr, stack,
+                         cast[pointer](d +% i*% mt.base.size),
+                         cast[pointer](s +% i*% mt.base.size), mt.base)
+  of tyRef:
+    let s2 = cast[PPointer](src)[]
+    if s2 == nil:
+      cast[PPointer](dest)[] = nil
+    else:
+      # we modify the header of the cell temporarily; instead of the type
+      # field we store a forwarding pointer. XXX This is bad when the cloning
+      # fails due to OOM etc.
+      let x = usrToCell(s2)
+      let forw = cast[int](x.typ)
+      if (forw and 1) == 1:
+        # we stored a forwarding pointer, so let's use that:
+        let z = cast[pointer](forw and not 1)
+        unsureAsgnRef(cast[PPointer](dest), z)
+      else:
+        let realType = x.typ
+        let z = newObj(realType, realType.base.size)
+
+        unsureAsgnRef(cast[PPointer](dest), z)
+        x.typ = cast[PNimType](cast[int](z) or 1)
+        genericDeepCopyAux(dr, stack, z, s2, realType.base)
+        x.typ = realType
+  else:
+    copyMem(dest, src, mt.size)
+
+proc joinAliveDataFromRegion*(dest: var MemRegion; src: var MemRegion;
+                              root: pointer): pointer =
+  # we mark the alive data and copy only alive data over to 'dest'.
+  # This is O(liveset) but it nicely compacts memory, so it's fine.
+  # We use the 'typ' field as a forwarding pointer. The forwarding
+  # pointers have bit 0 set, so we can disambiguate them.
+  # We allocate a temporary stack in 'src' that we later free:
+  var s: PointerStackChunk
+  s.len = 1
+  s.data[0] = root
+  while s.len > 0:
+    var p: pointer
+    if s.tail == nil:
+      p = s.data[s.len-1]
+      dec s.len
+    else:
+      p = s.tail.data[s.tail.len-1]
+      dec s.tail.len
+      if s.tail.len == 0:
+        unlink(s, s.tail)
+
+proc rawNewObj(r: var MemRegion, typ: PNimType, size: int): pointer =
+  var res = cast[ptr ObjHeader](alloc(r, size + sizeof(ObjHeader)))
+  res.typ = typ
+  if typ.finalizer != nil:
+    res.nextFinal = r.chunk.head
+    r.chunk.head = res
+  result = res +! sizeof(ObjHeader)
+
+proc newObj(typ: PNimType, size: int): pointer {.compilerRtl.} =
+  result = rawNewObj(typ, size, region)
+  zeroMem(result, size)
+  when defined(memProfiler): nimProfile(size)
+
+proc newObjNoInit(typ: PNimType, size: int): pointer {.compilerRtl.} =
+  result = rawNewObj(typ, size, region)
+  when defined(memProfiler): nimProfile(size)
+
+proc newSeq(typ: PNimType, len: int): pointer {.compilerRtl.} =
+  let size = addInt(mulInt(len, typ.base.size), GenericSeqSize)
+  result = newObj(typ, size)
+  cast[PGenericSeq](result).len = len
+  cast[PGenericSeq](result).reserved = len
+
+proc newObjRC1(typ: PNimType, size: int): pointer {.compilerRtl.} =
+  result = rawNewObj(typ, size, gch)
+  zeroMem(result, size)
+
+proc newSeqRC1(typ: PNimType, len: int): pointer {.compilerRtl.} =
+  let size = addInt(mulInt(len, typ.base.size), GenericSeqSize)
+  result = newObj(typ, size)
+  cast[PGenericSeq](result).len = len
+  cast[PGenericSeq](result).reserved = len
+
+proc growObj(old: pointer, newsize: int, gch: var GcHeap): pointer =
+  collectCT(gch)
+  var ol = usrToCell(old)
+  sysAssert(ol.typ != nil, "growObj: 1")
+  gcAssert(ol.typ.kind in {tyString, tySequence}, "growObj: 2")
+
+  var res = cast[PCell](rawAlloc(gch.region, newsize + sizeof(Cell)))
+  var elemSize = 1
+  if ol.typ.kind != tyString: elemSize = ol.typ.base.size
+
+  var oldsize = cast[PGenericSeq](old).len*elemSize + GenericSeqSize
+  copyMem(res, ol, oldsize + sizeof(Cell))
+  zeroMem(cast[pointer](cast[ByteAddress](res)+% oldsize +% sizeof(Cell)),
+          newsize-oldsize)
+  sysAssert((cast[ByteAddress](res) and (MemAlign-1)) == 0, "growObj: 3")
+  result = cellToUsr(res)
+
+proc growObj(old: pointer, newsize: int): pointer {.rtl.} =
+  result = growObj(old, newsize, region)
+