From 25f93309285147f8e1ee72a8da09359a197558a5 Mon Sep 17 00:00:00 2001
From: Jacek Sieka <arnetheduck@gmail.com>
Date: Fri, 25 Mar 2016 20:54:01 +0800
Subject: [PATCH 1/2] store block size in when using malloc and nogc

this allows for a correct implementation of realloc, which is needed as
code using it assumes new values will be zeroed out / nil
---
 lib/system/mmdisp.nim | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/lib/system/mmdisp.nim b/lib/system/mmdisp.nim
index 4b01cf4a87..76c1b476e1 100644
--- a/lib/system/mmdisp.nim
+++ b/lib/system/mmdisp.nim
@@ -389,15 +389,30 @@ elif defined(nogc) and defined(useMalloc):
 
   when not defined(useNimRtl):
     proc alloc(size: Natural): pointer =
-      result = cmalloc(size)
-      if result == nil: raiseOutOfMem()
+      var x = cmalloc(size + sizeof(size))
+      if x == nil: raiseOutOfMem()
+
+      cast[ptr int](x)[] = size
+      result = cast[pointer](cast[int](x) + sizeof(size))
+
     proc alloc0(size: Natural): pointer =
       result = alloc(size)
       zeroMem(result, size)
     proc realloc(p: pointer, newsize: Natural): pointer =
-      result = crealloc(p, newsize)
-      if result == nil: raiseOutOfMem()
-    proc dealloc(p: pointer) = cfree(p)
+      var x = cast[pointer](cast[int](p) - sizeof(newsize))
+      let oldsize = cast[ptr int](x)[]
+
+      x = crealloc(x, newsize + sizeof(newsize))
+
+      if x == nil: raiseOutOfMem()
+
+      cast[ptr int](x)[] = newsize
+      result = cast[pointer](cast[int](x) + sizeof(newsize))
+
+      if newsize > oldsize:
+        zeroMem(cast[pointer](cast[int](result) + oldsize), newsize - oldsize)
+
+    proc dealloc(p: pointer) = cfree(cast[pointer](cast[int](p) - sizeof(int)))
 
     proc allocShared(size: Natural): pointer =
       result = cmalloc(size)

From a2501321c39a89fb0bad52dcb8ef7c974d4ae5d2 Mon Sep 17 00:00:00 2001
From: Jacek Sieka <arnetheduck@gmail.com>
Date: Sat, 2 Apr 2016 21:15:10 +0800
Subject: [PATCH 2/2] document useMalloc changes

---
 doc/nimc.txt | 4 +++-
 web/news.txt | 6 +++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/doc/nimc.txt b/doc/nimc.txt
index e7cb570379..48dbaeb219 100644
--- a/doc/nimc.txt
+++ b/doc/nimc.txt
@@ -243,7 +243,9 @@ Define               Effect
 ``useFork``          Makes ``osproc`` use ``fork`` instead of ``posix_spawn``.
 ``useNimRtl``        Compile and link against ``nimrtl.dll``.
 ``useMalloc``        Makes Nim use C's `malloc`:idx: instead of Nim's
-                     own memory manager. This only works with ``gc:none``.
+                     own memory manager, ableit prefixing each allocation with
+                     its size to support clearing memory on reallocation.
+                     This only works with ``gc:none``.
 ``useRealtimeGC``    Enables support of Nim's GC for *soft* realtime
                      systems. See the documentation of the `gc <gc.html>`_
                      for further information.
diff --git a/web/news.txt b/web/news.txt
index e818ed66e7..f0f17448f6 100644
--- a/web/news.txt
+++ b/web/news.txt
@@ -20,7 +20,11 @@ Changes affecting backwards compatibility
   new experimental ``this`` pragma to achieve a similar effect to what the old ``using`` statement tried to achieve.
 - Typeless parameters have been removed from the language since it would
   clash with ``using``.
-
+- When using ``useMalloc``, an additional header containing the size of the
+  allocation will be allocated, to support zeroing memory on realloc as expected
+  by the language. With this change, ``alloc`` and ``dealloc`` are no longer
+  aliases for ``malloc`` and ``free`` - use ``c_malloc`` and ``c_free`` if
+  you need that.
 
 Library Additions
 -----------------