Add loadable modules using Daniel Colascione's ideas.scratch/dynamic-modules-2

See https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00960.html

* src/Makefile.in (base_obj): add module.o
  (LIBES): add -lltdl

* src/emacs.c (main): add syms_of_module

* src/lisp.h: add syms_of_module

* src/emacs_module.h: New file; emacs API for modules.

* src/module.c: New file; implement API.

* modules/basic/Makefile: New file; build example module on Linux.

* modules/basic/basic.c: New file; simple example module.

1 files changed, 64 insertions, 0 deletions

diff --git a/modules/basic/basic.c b/modules/basic/basic.c
new file mode 100644
index 00000000000..f288b3832ca
--- /dev/null
+++ b/modules/basic/basic.c
@@ -0,0 +1,64 @@
+/*
+
+  basic.c - sample module
+
+  This module provides a simple `basic-sum' function.
+
+  I've used the following prefixes throughout the code:
+  - Sfoo: subr (function wraper)
+  - Qfoo: symbol value
+  - Ffoo: function value
+
+*/
+
+#include <emacs_module.h>
+
+int plugin_is_GPL_compatible;
+
+/* C function we want to expose to emacs */
+static int64_t sum (int64_t a, int64_t b)
+{
+  return a + b;
+}
+
+/* Proper module subr that wraps the C function */
+static emacs_value Fsum (emacs_env *env, int nargs, emacs_value args[])
+{
+  int64_t a = env->fixnum_to_int (env, args[0]);
+  int64_t b = env->fixnum_to_int (env, args[1]);
+
+  int64_t r = sum(a, b);
+
+  return env->make_fixnum (env, r);
+}
+
+/* Binds NAME to FUN */
+static void bind_function (emacs_env *env, const char *name, emacs_value Ffun)
+{
+  emacs_value Qfset = env->intern (env, "fset");
+  emacs_value Qsym = env->intern (env, name);
+  emacs_value args[] = { Qsym, Ffun };
+
+  env->funcall (env, Qfset, 2, args);
+}
+
+/* Provide FEATURE to Emacs */
+static void provide (emacs_env *env, const char *feature)
+{
+  emacs_value Qfeat = env->intern (env, feature);
+  emacs_value Qprovide = env->intern (env, "provide");
+  emacs_value args[] = { Qfeat };
+
+  env->funcall (env, Qprovide, 1, args);
+}
+
+int emacs_module_init (struct emacs_runtime *ert)
+{
+  emacs_env *env = ert->get_environment (ert);
+  emacs_value Ssum = env->make_function (env, 2, 2, Fsum);
+
+  bind_function (env, "basic-sum", Ssum);
+  provide (env, "basic");
+
+  return 0;
+}