[project] Generate syscalls from new interface DSL

This change adds a new interface DSL for specifying objects (with
methods) and interfaces (that expose objects, and optionally have their
own methods).

Significant changes:

- Add the new scripts/definitions Python module to parse the DSL
- Add the new definitions directory containing DSL definition files
- Use cog to generate syscall-related code in kernel and libj6
- Unify ordering of pointer + length pairs in interfaces

scripts/definitions/generate.py

@@ -0,0 +1,62 @@
+def generate_template(template, outfile, **kwargs):
+    from hashlib import md5
+    from os import makedirs
+    from os.path import dirname, exists
+
+    content = template.render(**kwargs)
+    h = md5(content.encode('utf-8')).hexdigest()
+
+    if exists(outfile):
+        existing = open(outfile, 'r').read().encode('utf-8')
+        if md5(existing).hexdigest() == h:
+            return False
+
+    makedirs(dirname(outfile), exist_ok=True)
+    open(outfile, 'w').write(content)
+
+    return True
+
+def generate(ctx, outdir, template_type):
+    from os.path import basename, join, split, splitext
+    from jinja2 import Environment, PackageLoader
+
+    for name, interface in ctx.interfaces.items():
+        base = "_".join(sorted(interface.options))
+
+        path = join("templates", base, template_type)
+        env = Environment(
+            loader = PackageLoader('definitions', package_path=path),
+            trim_blocks = True, lstrip_blocks = True)
+
+        env.filters
+
+        for template_name in env.list_templates():
+            template = env.get_template(template_name)
+
+            basepath, filename = split(template_name)
+            filename, ext = splitext(filename)
+
+            if filename == "_object_":
+                for obj in ctx.objects.values():
+                    outfile = join(outdir, basepath, obj.name + ext)
+                    wrote = generate_template(
+                                template, outfile,
+                                filename=obj.name + ext,
+                                basepath=basepath,
+                                object=obj,
+                                interface=interface,
+                                objects=ctx.objects)
+
+                    if wrote and ctx.verbose:
+                        print(f"Writing {outfile}")
+
+            else:
+                outfile = join(outdir, template_name)
+                wrote = generate_template(
+                            template, outfile,
+                            filename=basename(template_name),
+                            interface=interface,
+                            objects=ctx.objects)
+
+                if wrote and ctx.verbose:
+                    print(f"Writing {outfile}")