Bench on Linux (#581)

* Make benchmarking work on Linux

* Rename `mac_osx_time.c` to less platform-specific `time.c`

* Semi missing.

Co-authored-by: Cristiano Calcagno <cristianoc@users.noreply.github.com>

Author: nkrkv

benchmarks/dune

@@ -2,12 +2,19 @@
  (name benchmark)
  (public_name bench)
  (enabled_if
-  (= %{system} macosx))
+  (or
+   (= %{system} macosx)
+   ; or one of Linuxes (see https://github.com/ocaml/ocaml/issues/10613)
+   (= %{system} linux)
+   (= %{system} linux_elf)
+   (= %{system} elf)
+   (= %{system} linux_eabihf)
+   (= %{system} linux_eabi)))
  (flags
   (-open Syntax -open Compilerlibs406))
  (foreign_stubs
   (language c)
-  (names mac_osx_time))
+  (names time))
  (libraries syntax compilerlibs406))
 
 (data_only_dirs data)

benchmarks/mac_osx_time.c

@@ -0,0 +1,44 @@
+#include <caml/mlvalues.h>
+#include <caml/alloc.h>
+
+//
+// Platform-specific includes
+//
+#if (defined(__MACH__) && defined(__APPLE__))
+#include <mach/mach_time.h>
+#elif defined(__linux__)
+#include <time.h>
+#endif
+
+//
+// Platform-specific globals
+//
+#if (defined(__MACH__) && defined(__APPLE__))
+static mach_timebase_info_data_t info;
+#endif
+
+//
+// Exported functions
+//
+CAMLprim value caml_mach_initialize(value unit) {
+#if (defined(__MACH__) && defined(__APPLE__))
+  mach_timebase_info(&info);
+#endif
+
+  return Val_unit;
+}
+
+CAMLprim value caml_mach_absolute_time(value unit) {
+  uint64_t result = 0;
+
+#if (defined(__MACH__) && defined(__APPLE__))
+  uint64_t now = mach_absolute_time();
+  result = (now * info.numer) / info.denom;
+#elif defined(__linux__)
+  struct timespec now;
+  clock_gettime(CLOCK_MONOTONIC, &now);
+  result = now.tv_sec * 1000 + now.tv_nsec / 1000000;
+#endif
+
+  return caml_copy_int64(result);
+}