Add experimental helpers for calling kernel functions and writing to …

…memory

These are highly-requested features that I didn't implement for awhile
because I thought they would be too difficult or hacky. The approach
that I finally came up with is slightly deranged but solid: we manually
generate a kernel module ELF file and machine code to do a function
call. An alternative approach that I tried was generating C source code
for a kernel module and building it, but that relies on having
kernel-devel and a compatible toolchain installed, and it's slow. (Kudos
to Matthew Wilcox for suggesting the kernel module approach last year:
https://lwn.net/Articles/953256/.)

For now, this is under a new drgn.helpers.experimental package, in the
drgn.helpers.experimental.kmodify module, with no stability guarantees,
but we still have tests for it.

Signed-off-by: Omar Sandoval <[email protected]>

drgn/helpers/experimental/__init__.py

@@ -0,0 +1,11 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+"""
+Experimental
+------------
+
+The ``drgn.helpers.experimental`` package contains experimental helpers with no
+stability guarantees. They may change, move to another package, or be removed.
+They are not automatically imported by the CLI.
+"""