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>

1 files changed, 141 insertions, 0 deletions

diff --git a/m4/ax_gcc_var_attribute.m4 b/m4/ax_gcc_var_attribute.m4
new file mode 100644
index 00000000000..247cc4ab3eb
--- /dev/null
+++ b/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])
+])