A year ago, we discussed the possibility of having a module that implements
immutable objects, along the lines of
<https://lists.gnu.org/archive/html/bug-gnulib/2019-12/msg00231.html> and
<https://lists.gnu.org/archive/html/bug-gnulib/2019-12/msg00235.html>.

Here's the implementation. Quite easy, now that the 'ssfmalloc' module is
present.

Note: In <https://lists.gnu.org/archive/html/bug-gnulib/2019-12/msg00240.html>
we discussed the possible need for data cache flushing. In my tests, it is
not needed (so far). Please report if you find a platform where this module
introduces non-deterministic crashes.


2021-01-09  Bruno Haible  <bruno@clisp.org>

	immutable: Add tests.
	* tests/test-immutable.sh: New file.
	* tests/test-immutable.c: New file.
	* modules/immutable-tests: New file.

	immutable: New module.
	* lib/immutable.h: New file.
	* lib/immutable.c: New file.
	* m4/immutable.m4: New file.
	* m4/mprotect.m4: New file, based on libffcall/m4/codeexec.m4.
	* modules/immutable: New file.