Add dynamic module module support

* configure.ac: Add '--with-modules' option.  Conditionally add
  dynlib.o and module.o to the list of objects.  Add any system
  specific flags to the linker flags to support dynamic libraries.
* m4/ax_gcc_var_attribute.m4: Add autoconf extension to test gcc
  attributes.
* src/Makefile.in: Conditionally add module objects and linker flags.
* src/alloc.c (garbage_collect_1): protect module local values from
  GC.
* src/lisp.h: Add 'module_init' and 'syms_of_module' prototypes.
* src/emacs_module.h: New header file included by modules.  Public
  module API.
* src/module.c: New module implementation file.

Co-authored-by: Philipp Stephani <phst@google.com>

configure.ac

@@ -353,6 +353,7 @@ OPTION_DEFAULT_ON([gsettings],[don't compile with GSettings support])
 OPTION_DEFAULT_ON([selinux],[don't compile with SELinux support])
 OPTION_DEFAULT_ON([gnutls],[don't use -lgnutls for SSL/TLS support])
 OPTION_DEFAULT_ON([zlib],[don't compile with zlib decompression support])
+OPTION_DEFAULT_OFF([modules],[compile with dynamic modules support])
 
 AC_ARG_WITH([file-notification],[AS_HELP_STRING([--with-file-notification=LIB],
  [use a file notification library (LIB one of: yes, gfile, inotify, w32, no)])],
@@ -2191,6 +2192,9 @@ LIBS="$LIBS_SYSTEM $LIBS"
 dnl FIXME replace main with a function we actually want from this library.
 AC_CHECK_LIB(Xbsd, main, LD_SWITCH_X_SITE="$LD_SWITCH_X_SITE -lXbsd")
 
+dnl Check for C11 threads.
+AC_CHECK_HEADERS_ONCE(threads.h)
+
 dnl Check for the POSIX thread library.
 LIB_PTHREAD=
 AC_CHECK_HEADERS_ONCE(pthread.h)
@@ -3285,6 +3289,48 @@ if test "${HAVE_ZLIB}" = "yes"; then
 fi
 AC_SUBST(LIBZ)
 
+### Dynamic modules support
+LIBMODULES=
+HAVE_MODULES=no
+MODULES_OBJ=
+MODULES_SUFFIX=
+if test "${with_modules}" != "no"; then
+  if test "$opsys" = "gnu-linux"; then
+    LIBMODULES="-ldl"
+    MODULES_SUFFIX=".so"
+    HAVE_MODULES=yes
+  elif test "$opsys" = "cygwin"; then
+    # XXX: not tested
+    LIBMODULES="-lcygwin"
+    MODULES_SUFFIX=".dll"
+    HAVE_MODULES=yes
+  elif test "$opsys" = "darwin"; then
+    MODULES_SUFFIX=".so"
+    HAVE_MODULES=yes
+  elif test "$opsys" = "mingw32"; then
+    MODULES_SUFFIX=".dll"
+    HAVE_MODULES=yes
+  else
+    # BSD system have dlopen in the libc
+    AC_CHECK_FUNC(dlopen, [MODULES_SUFFIX=".so"]
+                          [HAVE_MODULES=yes], [])
+  fi
+
+  if test "${HAVE_MODULES}" = no; then
+    AC_MSG_ERROR([Dynamic modules are not supported on your system])
+  fi
+fi
+
+if test "${HAVE_MODULES}" = yes; then
+   MODULES_OBJ="dynlib.o module.o"
+   AC_DEFINE(HAVE_MODULES, 1, [Define to 1 if dynamic modules are enabled])
+   AC_DEFINE_UNQUOTED(MODULES_SUFFIX, "$MODULES_SUFFIX", [System extension for dynamic libraries])
+fi
+AC_SUBST(MODULES_OBJ)
+AC_SUBST(LIBMODULES)
+AX_GCC_VAR_ATTRIBUTE(cleanup)
+AC_CHECK_FUNCS(dladdr)
+
 ### Use -lpng if available, unless '--with-png=no'.
 HAVE_PNG=no
 LIBPNG=
@@ -5175,7 +5221,7 @@ optsep=
 emacs_config_features=
 for opt in XAW3D XPM JPEG TIFF GIF PNG RSVG CAIRO IMAGEMAGICK SOUND GPM DBUS \
   GCONF GSETTINGS NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT \
-  LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS X_TOOLKIT X11 NS; do
+  LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS X_TOOLKIT X11 NS MODULES; do
 
     case $opt in
       NOTIFY|ACL) eval val=\${${opt}_SUMMARY} ;;
@@ -5223,6 +5269,7 @@ AS_ECHO(["  Does Emacs use -lXaw3d?                                 ${HAVE_XAW3D
   Does Emacs use -lotf?                                   ${HAVE_LIBOTF}
   Does Emacs use -lxft?                                   ${HAVE_XFT}
   Does Emacs directly use zlib?                           ${HAVE_ZLIB}
+  Does Emacs has dynamic modules support?                 ${HAVE_MODULES}
   Does Emacs use toolkit scroll bars?                     ${USE_TOOLKIT_SCROLL_BARS}
 "])
 

m4/ax_gcc_var_attribute.m4

@@ -0,0 +1,141 @@
+# ===========================================================================
+#   http://www.gnu.org/software/autoconf-archive/ax_gcc_var_attribute.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_GCC_VAR_ATTRIBUTE(ATTRIBUTE)
+#
+# DESCRIPTION
+#
+#   This macro checks if the compiler supports one of GCC's variable
+#   attributes; many other compilers also provide variable attributes with
+#   the same syntax. Compiler warnings are used to detect supported
+#   attributes as unsupported ones are ignored by default so quieting
+#   warnings when using this macro will yield false positives.
+#
+#   The ATTRIBUTE parameter holds the name of the attribute to be checked.
+#
+#   If ATTRIBUTE is supported define HAVE_VAR_ATTRIBUTE_<ATTRIBUTE>.
+#
+#   The macro caches its result in the ax_cv_have_var_attribute_<attribute>
+#   variable.
+#
+#   The macro currently supports the following variable attributes:
+#
+#    aligned
+#    cleanup
+#    common
+#    nocommon
+#    deprecated
+#    mode
+#    packed
+#    tls_model
+#    unused
+#    used
+#    vector_size
+#    weak
+#    dllimport
+#    dllexport
+#    init_priority
+#
+#   Unsuppored variable attributes will be tested against a global integer
+#   variable and without any arguments given to the attribute itself; the
+#   result of this check might be wrong or meaningless so use with care.
+#
+# LICENSE
+#
+#   Copyright (c) 2013 Gabriele Svelto <gabriele.svelto@gmail.com>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved.  This file is offered as-is, without any
+#   warranty.
+
+#serial 3
+
+AC_DEFUN([AX_GCC_VAR_ATTRIBUTE], [
+    AS_VAR_PUSHDEF([ac_var], [ax_cv_have_var_attribute_$1])
+
+    AC_CACHE_CHECK([for __attribute__(($1))], [ac_var], [
+        AC_LINK_IFELSE([AC_LANG_PROGRAM([
+            m4_case([$1],
+                [aligned], [
+                    int foo __attribute__(($1(32)));
+                ],
+                [cleanup], [
+                    int bar(int *t) { return *t; };
+                ],
+                [common], [
+                    int foo __attribute__(($1));
+                ],
+                [nocommon], [
+                    int foo __attribute__(($1));
+                ],
+                [deprecated], [
+                    int foo __attribute__(($1)) = 0;
+                ],
+                [mode], [
+                    long foo __attribute__(($1(word)));
+                ],
+                [packed], [
+                    struct bar {
+                        int baz __attribute__(($1));
+                    };
+                ],
+                [tls_model], [
+                    __thread int bar1 __attribute__(($1("global-dynamic")));
+                    __thread int bar2 __attribute__(($1("local-dynamic")));
+                    __thread int bar3 __attribute__(($1("initial-exec")));
+                    __thread int bar4 __attribute__(($1("local-exec")));
+                ],
+                [unused], [
+                    int foo __attribute__(($1));
+                ],
+                [used], [
+                    int foo __attribute__(($1));
+                ],
+                [vector_size], [
+                    int foo __attribute__(($1(16)));
+                ],
+                [weak], [
+                    int foo __attribute__(($1));
+                ],
+                [dllimport], [
+                    int foo __attribute__(($1));
+                ],
+                [dllexport], [
+                    int foo __attribute__(($1));
+                ],
+                [init_priority], [
+                    struct bar { bar() {} ~bar() {} };
+                    bar b __attribute__(($1(65535/2)));
+                ],
+                [
+                 m4_warn([syntax], [Unsupported attribute $1, the test may fail])
+                 int foo __attribute__(($1));
+                ]
+            )], [
+            m4_case([$1],
+                [cleanup], [
+                    int foo __attribute__(($1(bar))) = 0;
+                    foo = foo + 1;
+                ],
+                []
+            )])
+            ],
+            dnl GCC doesn't exit with an error if an unknown attribute is
+            dnl provided but only outputs a warning, so accept the attribute
+            dnl only if no warning were issued.
+            [AS_IF([test -s conftest.err],
+                [AS_VAR_SET([ac_var], [no])],
+                [AS_VAR_SET([ac_var], [yes])])],
+            [AS_VAR_SET([ac_var], [no])])
+    ])
+
+    AS_IF([test yes = AS_VAR_GET([ac_var])],
+        [AC_DEFINE_UNQUOTED(AS_TR_CPP(HAVE_VAR_ATTRIBUTE_$1), 1,
+            [Define to 1 if the system has the `$1' variable attribute])], [])
+
+    AS_VAR_POPDEF([ac_var])
+])

src/Makefile.in

@@ -230,6 +230,11 @@ LIBXML2_CFLAGS = @LIBXML2_CFLAGS@
 
 LIBZ = @LIBZ@
 
+## system-specific libs for dynamic modules, else empty
+LIBMODULES = @LIBMODULES@
+## dynlib.o module.o if modules enabled, else empty
+MODULES_OBJ = @MODULES_OBJ@
+
 XRANDR_LIBS = @XRANDR_LIBS@
 XRANDR_CFLAGS = @XRANDR_CFLAGS@
 
@@ -377,7 +382,7 @@ base_obj = dispnew.o frame.o scroll.o xdisp.o menu.o $(XMENU_OBJ) window.o \
 	minibuf.o fileio.o dired.o \
 	cmds.o casetab.o casefiddle.o indent.o search.o regex.o undo.o \
 	alloc.o data.o doc.o editfns.o callint.o \
-	eval.o floatfns.o fns.o font.o print.o lread.o \
+	eval.o floatfns.o fns.o font.o print.o lread.o $(MODULES_OBJ) \
 	syntax.o $(UNEXEC_OBJ) bytecode.o \
 	process.o gnutls.o callproc.o \
 	region-cache.o sound.o atimer.o \
@@ -468,7 +473,7 @@ LIBES = $(LIBS) $(W32_LIBS) $(LIBS_GNUSTEP) $(LIBX_BASE) $(LIBIMAGE) \
    $(LIBS_TERMCAP) $(GETLOADAVG_LIBS) $(SETTINGS_LIBS) $(LIBSELINUX_LIBS) \
    $(FREETYPE_LIBS) $(FONTCONFIG_LIBS) $(LIBOTF_LIBS) $(M17N_FLT_LIBS) \
    $(LIBGNUTLS_LIBS) $(LIB_PTHREAD) \
-   $(GFILENOTIFY_LIBS) $(LIB_MATH) $(LIBZ)
+   $(GFILENOTIFY_LIBS) $(LIB_MATH) $(LIBZ) $(LIBMODULES)
 
 $(leimdir)/leim-list.el: bootstrap-emacs$(EXEEXT)
 	$(MAKE) -C ../leim leim-list.el EMACS="$(bootstrap_exe)"

src/alloc.c

@@ -5574,6 +5574,10 @@ garbage_collect_1 (void *end)
   mark_fringe_data ();
 #endif
 
+#ifdef HAVE_MODULES
+  mark_modules ();
+#endif
+
   /* Everything is now marked, except for the data in font caches,
      undo lists, and finalizers.  The first two are compacted by
      removing an items which aren't reachable otherwise.  */

src/emacs.c

@@ -776,6 +776,10 @@ main (int argc, char **argv)
 
   atexit (close_output_streams);
 
+#ifdef HAVE_MODULES
+  module_init ();
+#endif
+
   sort_args (argc, argv);
   argc = 0;
   while (argv[argc]) argc++;
@@ -1450,6 +1454,11 @@ Using an Emacs configured with --with-x-toolkit=lucid does not have this problem
       syms_of_terminal ();
       syms_of_term ();
       syms_of_undo ();
+
+#ifdef HAVE_MODULES
+      syms_of_module ();
+#endif
+
 #ifdef HAVE_SOUND
       syms_of_sound ();
 #endif

src/emacs_module.h

@@ -0,0 +1,230 @@
+/*
+  emacs_module.h - Module API
+  Copyright (C) 2015 Free Software Foundation, Inc.
+
+  This file is part of GNU Emacs.
+
+  GNU Emacs is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  GNU Emacs is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef EMACS_MODULE_H
+#define EMACS_MODULE_H
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+#ifdef __cplusplus
+#define EMACS_EXTERN_C_BEGIN extern "C" {
+#define EMACS_EXTERN_C_END }
+#else
+#define EMACS_EXTERN_C_BEGIN
+#define EMACS_EXTERN_C_END
+#endif
+
+#if defined(__cplusplus) && __cplusplus >= 201103L
+#define EMACS_NOEXCEPT noexcept
+#else
+#define EMACS_NOEXCEPT
+#endif
+
+EMACS_EXTERN_C_BEGIN
+
+/* Current environement */
+typedef struct emacs_env_25 emacs_env;
+
+/* Opaque structure pointer representing an Emacs Lisp value */
+typedef struct emacs_value_tag* emacs_value;
+
+enum emacs_arity {
+  emacs_variadic_function = -2
+};
+
+/* Struct passed to a module init function (emacs_module_init) */
+struct emacs_runtime {
+  /* Structure size (for version checking) */
+  size_t size;
+
+  /* Private data; users should not touch this */
+  struct emacs_runtime_private *private_members;
+
+  /* Returns an environment pointer. */
+  emacs_env* (*get_environment)(struct emacs_runtime *ert);
+};
+
+
+/* Function prototype for the module init function */
+typedef int (*emacs_init_function)(struct emacs_runtime *ert);
+
+/* Function prototype for the module Lisp functions */
+typedef emacs_value (*emacs_subr)(emacs_env *env,
+                                  int nargs,
+                                  emacs_value args[],
+                                  void *data);
+
+/* Function prototype for module user-pointer finalizers */
+typedef void (*emacs_finalizer_function)(void*);
+
+/* Possible Emacs function call outcomes. */
+enum emacs_funcall_exit {
+  /* Function has returned normally. */
+  emacs_funcall_exit_return = 0,
+  /* Function has signaled an error using `signal'. */
+  emacs_funcall_exit_signal = 1,
+  /* Function has exit using `throw'. */
+  emacs_funcall_exit_throw = 2,
+};
+
+struct emacs_env_25 {
+  /*
+   * Structure size (for version checking)
+   */
+
+  size_t size;
+
+  /* Private data; users should not touch this */
+  struct emacs_env_private *private_members;
+
+  /*
+   * Memory management
+   */
+
+
+  emacs_value (*make_global_ref)(emacs_env *env,
+                                 emacs_value any_reference);
+
+  void (*free_global_ref)(emacs_env *env,
+                          emacs_value global_reference);
+
+  /*
+   * Non-local exit handling
+   */
+
+  enum emacs_funcall_exit (*non_local_exit_check)(emacs_env *env);
+
+  void (*non_local_exit_clear)(emacs_env *env);
+
+  enum emacs_funcall_exit (*non_local_exit_get)(emacs_env *env,
+                                       emacs_value *non_local_exit_symbol_out,
+                                       emacs_value *non_local_exit_data_out);
+
+  void (*non_local_exit_signal)(emacs_env *env,
+                       emacs_value non_local_exit_symbol,
+                       emacs_value non_local_exit_data);
+
+  void (*non_local_exit_throw)(emacs_env *env,
+                      emacs_value tag,
+                      emacs_value value);
+
+  /*
+   * Function registration
+   */
+
+  emacs_value (*make_function)(emacs_env *env,
+                               int min_arity,
+                               int max_arity,
+                               emacs_value (*function)(emacs_env*, int, emacs_value*, void*) EMACS_NOEXCEPT,
+                               const char *documentation,
+                               void *data);
+
+  emacs_value (*funcall)(emacs_env *env,
+                         emacs_value function,
+                         int nargs,
+                         emacs_value args[]);
+
+  emacs_value (*intern)(emacs_env *env,
+                        const char *symbol_name);
+
+  /*
+   * Type conversion
+   */
+
+  emacs_value (*type_of)(emacs_env *env,
+                         emacs_value value);
+
+  bool (*is_not_nil)(emacs_env *env, emacs_value value);
+
+  bool (*eq)(emacs_env *env, emacs_value a, emacs_value b);
+
+  int64_t (*extract_integer)(emacs_env *env,
+                             emacs_value value);
+
+  emacs_value (*make_integer)(emacs_env *env,
+                              int64_t value);
+
+  double (*extract_float)(emacs_env *env,
+                          emacs_value value);
+
+  emacs_value (*make_float)(emacs_env *env,
+                            double value);
+
+  /*
+   * Copy the content of the lisp string VALUE to BUFFER as an utf8
+   * null-terminated string.
+   *
+   * SIZE must point to the total size of the buffer.  If BUFFER is
+   * NULL or if SIZE is not big enough, write the required buffer size
+   * to SIZE and return false.
+   *
+   * Note that SIZE must include the last null byte (e.g. "abc" needs
+   * a buffer of size 4).
+   *
+   * Returns true if the string was successfully copied.
+   */
+
+  bool (*copy_string_contents)(emacs_env *env,
+                               emacs_value value,
+                               char *buffer,
+                               size_t *size_inout);
+
+  /*
+   * Create a lisp string from a utf8 encoded string.
+   */
+  emacs_value (*make_string)(emacs_env *env,
+                             const char *contents, size_t length);
+
+  /*
+   * Embedded pointer type
+   */
+  emacs_value (*make_user_ptr)(emacs_env *env,
+                               void (*fin)(void *) EMACS_NOEXCEPT,
+                               void *ptr);
+
+  void* (*get_user_ptr)(emacs_env *env, emacs_value uptr);
+  void (*set_user_ptr)(emacs_env *env, emacs_value uptr, void *ptr);
+
+  void (*(*get_user_finalizer)(emacs_env *env, emacs_value uptr))(void *) EMACS_NOEXCEPT;
+  void (*set_user_finalizer)(emacs_env *env,
+                             emacs_value uptr,
+                             void (*fin)(void *) EMACS_NOEXCEPT);
+
+  /*
+   * Vector functions
+   */
+  emacs_value (*vec_get) (emacs_env *env,
+			  emacs_value vec,
+			  size_t i);
+
+  void (*vec_set) (emacs_env *env,
+		   emacs_value vec,
+		   size_t i,
+		   emacs_value val);
+
+  size_t (*vec_size) (emacs_env *env,
+		      emacs_value vec);
+};
+
+EMACS_EXTERN_C_END
+
+#endif /* EMACS_MODULE_H */

src/lisp.h

@@ -3916,6 +3916,10 @@ extern bool let_shadows_global_binding_p (Lisp_Object symbol);
 /* Defined in alloc.c.  */
 extern Lisp_Object make_user_ptr (void (*finalizer) (void*), void *p);
 
+/* Defined in module.c.  */
+extern void module_init (void);
+extern void mark_modules (void);
+extern void syms_of_module (void);
 #endif
 
 /* Defined in editfns.c.  */