caml_alloc() takes units of Wsize (word size), not bytes.  As a consequence,
we're allocating 4 or 8 times too much memory.

Ocaml has a helper, Wsize_bsize(), but it truncates cases which aren't an
exact multiple.  Use a BUILD_BUG_ON() to cover the potential for truncation,
as there's no rounding-up form of the helper.

Fixes: 8b7ce06a2d34 ("ocaml: Add XC bindings.")
Fixes: d3e649277a13 ("ocaml: add mmap bindings implementation.")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Christian Lindig <christian.lindig@citrix.com>
CC: David Scott <dave@recoil.org>
CC: Edwin Török <edwin.torok@cloud.com>
CC: Rob Hoes <Rob.Hoes@citrix.com>
---
 tools/ocaml/libs/mmap/Makefile        | 2 ++
 tools/ocaml/libs/mmap/xenmmap_stubs.c | 6 +++++-
 tools/ocaml/libs/xc/xenctrl_stubs.c   | 5 ++++-
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/tools/ocaml/libs/mmap/Makefile b/tools/ocaml/libs/mmap/Makefile
index a62153713571..855b8b2c9877 100644
--- a/tools/ocaml/libs/mmap/Makefile
+++ b/tools/ocaml/libs/mmap/Makefile
@@ -2,6 +2,8 @@ OCAML_TOPLEVEL=$(CURDIR)/../..
 XEN_ROOT=$(OCAML_TOPLEVEL)/../..
 include $(OCAML_TOPLEVEL)/common.make
 
+CFLAGS += $(CFLAGS_xeninclude)
+
 OBJS = xenmmap
 INTF = $(foreach obj, $(OBJS),$(obj).cmi)
 LIBS = xenmmap.cma xenmmap.cmxa
diff --git a/tools/ocaml/libs/mmap/xenmmap_stubs.c b/tools/ocaml/libs/mmap/xenmmap_stubs.c
index e03951d781bb..d623ad390e40 100644
--- a/tools/ocaml/libs/mmap/xenmmap_stubs.c
+++ b/tools/ocaml/libs/mmap/xenmmap_stubs.c
@@ -21,6 +21,8 @@
 #include <errno.h>
 #include "mmap_stubs.h"
 
+#include <xen-tools/libs.h>
+
 #include <caml/mlvalues.h>
 #include <caml/memory.h>
 #include <caml/alloc.h>
@@ -59,7 +61,9 @@ CAMLprim value stub_mmap_init(value fd, value pflag, value mflag,
 	default: caml_invalid_argument("maptype");
 	}
 
-	result = caml_alloc(sizeof(struct mmap_interface), Abstract_tag);
+	BUILD_BUG_ON((sizeof(struct mmap_interface) % sizeof(value)) != 0);
+	result = caml_alloc(Wsize_bsize(sizeof(struct mmap_interface)),
+			    Abstract_tag);
 
 	if (mmap_interface_init(Intf_val(result), Int_val(fd),
 	                        c_pflag, c_mflag,
diff --git a/tools/ocaml/libs/xc/xenctrl_stubs.c b/tools/ocaml/libs/xc/xenctrl_stubs.c
index 728818445975..fd1f306f0202 100644
--- a/tools/ocaml/libs/xc/xenctrl_stubs.c
+++ b/tools/ocaml/libs/xc/xenctrl_stubs.c
@@ -1031,7 +1031,10 @@ CAMLprim value stub_map_foreign_range(value xch, value dom,
 	uint32_t c_dom;
 	unsigned long c_mfn;
 
-	result = caml_alloc(sizeof(struct mmap_interface), Abstract_tag);
+	BUILD_BUG_ON((sizeof(struct mmap_interface) % sizeof(value)) != 0);
+	result = caml_alloc(Wsize_bsize(sizeof(struct mmap_interface)),
+			    Abstract_tag);
+
 	intf = (struct mmap_interface *) result;
 
 	intf->len = Int_val(size);
-- 
2.11.0