On 28/08/2024 3:15 pm, Edwin Torok wrote:
> On Wed, Aug 28, 2024 at 2:30 PM Andrew Cooper <andrew.coop...@citrix.com>
> wrote:
>> ... rather than having each library implement its own subset.
>>
>> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
>> ---
>> CC: Christian Lindig <christian.lin...@citrix.com>
>> CC: David Scott <d...@recoil.org>
>> CC: Edwin Török <edwin.to...@cloud.com>
>> CC: Rob Hoes <rob.h...@citrix.com>
>> CC: Andrii Sultanov <andrii.sulta...@cloud.com>
>>
>> Broken out of a larger series, to help Andrii with his dynlib work.
>> ---
>> tools/ocaml/libs/xc/Makefile | 2 +-
>> tools/ocaml/libs/xc/xenctrl_stubs.c | 13 +++----------
>> tools/ocaml/libs/xen-caml-compat.h | 23 +++++++++++++++++++++++
>> 3 files changed, 27 insertions(+), 11 deletions(-)
>> create mode 100644 tools/ocaml/libs/xen-caml-compat.h
>>
>> diff --git a/tools/ocaml/libs/xc/Makefile b/tools/ocaml/libs/xc/Makefile
>> index 1d9fecb06ef2..cdf4d01dac52 100644
>> --- a/tools/ocaml/libs/xc/Makefile
>> +++ b/tools/ocaml/libs/xc/Makefile
>> @@ -2,7 +2,7 @@ OCAML_TOPLEVEL=$(CURDIR)/../..
>> XEN_ROOT=$(OCAML_TOPLEVEL)/../..
>> include $(OCAML_TOPLEVEL)/common.make
>>
>> -CFLAGS += -I../mmap $(CFLAGS_libxenctrl) $(CFLAGS_libxenguest)
>> +CFLAGS += -I../ -I../mmap $(CFLAGS_libxenctrl) $(CFLAGS_libxenguest)
>> CFLAGS += $(APPEND_CFLAGS)
>> OCAMLINCLUDE += -I ../mmap -I ../eventchn
>>
>> diff --git a/tools/ocaml/libs/xc/xenctrl_stubs.c
>> b/tools/ocaml/libs/xc/xenctrl_stubs.c
>> index a52908012960..c78191f95abc 100644
>> --- a/tools/ocaml/libs/xc/xenctrl_stubs.c
>> +++ b/tools/ocaml/libs/xc/xenctrl_stubs.c
>> @@ -25,6 +25,8 @@
>> #include <caml/fail.h>
>> #include <caml/callback.h>
>>
>> +#include "xen-caml-compat.h"
>> +
>> #include <sys/mman.h>
>> #include <stdint.h>
>> #include <string.h>
>> @@ -37,14 +39,6 @@
>>
>> #include "mmap_stubs.h"
>>
>> -#ifndef Val_none
>> -#define Val_none (Val_int(0))
>> -#endif
>> -
>> -#ifndef Tag_some
>> -#define Tag_some 0
>> -#endif
>> -
>> static inline xc_interface *xch_of_val(value v)
>> {
>> xc_interface *xch = *(xc_interface **)Data_custom_val(v);
>> @@ -744,8 +738,7 @@ CAMLprim value stub_xc_evtchn_status(value xch_val,
>> value domid, value port)
>> Store_field(result_status, 0, Val_int(status.vcpu));
>> Store_field(result_status, 1, stat);
>>
>> - result = caml_alloc_small(1, Tag_some);
>> - Store_field(result, 0, result_status);
>> + result = caml_alloc_some(result_status);
>>
>> CAMLreturn(result);
>> }
>> diff --git a/tools/ocaml/libs/xen-caml-compat.h
>> b/tools/ocaml/libs/xen-caml-compat.h
>> new file mode 100644
>> index 000000000000..b4a0ca4ce90c
>> --- /dev/null
>> +++ b/tools/ocaml/libs/xen-caml-compat.h
>> @@ -0,0 +1,23 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-only WITH OCaml-LGPL-linking-exception
>> */
>> +#ifndef XEN_CAML_COMPAT_H
>> +#define XEN_CAML_COMPAT_H
>> +
>> +#ifndef Val_none /* Option handling. Compat for Ocaml < 4.12 */
>> +
>> +#define Val_none Val_int(0)
>> +#define Tag_some 0
>> +#define Some_val(v) Field(v, 0)
>> +
>> +static inline value caml_alloc_some(value v)
>> +{
>> + CAMLparam1(v);
>> +
>> + value some = caml_alloc_small(1, Tag_some);
>> + Store_field(some, 0, v);
> The compiler uses Field() rather than Store_field() here.
> I think using Store_field here can potentially read uninitialized
> data, because 'caml_alloc_small' gives you uninitialized memory
> that you must immediately fill with valid values.
> Looking at the implementation Store_field calls caml_modify which will
> read the old value to figure out whether it was in minor or major
> heap,
> and doing that on uninitialized data is unpredictable.
>
> We should follow what the manual says and use Field() when
> caml_alloc_small() is used, and use Store_field() when caml_alloc() is
> used,
> and not attempt to mix them:
> See https://ocaml.org/manual/5.2/intfc.html#ss:c-low-level-gc-harmony
Lovely, this got changed in Ocaml with no information or justification...
https://github.com/ocaml/ocaml/pull/9819
I'll resync this locally, but I shaltn't repost.
~Andrew
