Add a section about debugging tips in user guide (#987)

Co-authored-by: Kunshan Wang <wks1986@gmail.com>

Author: qinsoon

docs/userguide/src/SUMMARY.md

@@ -31,6 +31,8 @@
     - [How to Undertake a Port](portingguide/howto/prefix.md)
         - [NoGC](portingguide/howto/nogc.md)
         - [Next Steps](portingguide/howto/next_steps.md)
+    - [Debugging Tips](portingguide/debugging/prefix.md)
+        - [Enabling Debug Assertions](portingguide/debugging/assertions.md)
     - [Performance Tuning](portingguide/perf_tuning/prefix.md)
         - [Link Time Optimization](portingguide/perf_tuning/lto.md)
         - [Optimizing Allocation](portingguide/perf_tuning/alloc.md)

docs/userguide/src/portingguide/debugging/assertions.md

@@ -0,0 +1,15 @@
+# Enabling debug assertions
+
+MMTk is implemented with an extensive amount of assertions to ensure the correctness.
+We strongly recommend using a debug build of MMTk that includes all the debugging assertions
+when one is developing on a MMTk binding. The assertions are normal Rust `debug_assert!`,
+and they can be turned on in a release build with Rust flags (https://doc.rust-lang.org/cargo/reference/profiles.html#debug-assertions).
+
+## Extreme debugging assertions
+
+In addition to the normal debugging assertions, MMTk also has a set of
+optional runtime checks that can be turned on by enabling the feature `extreme_assertions`.
+These usually include checks that are too expensive (even in a debug build) that we do not
+want to enable by default.
+
+You should make sure your MMTk binding can pass all the assertions (including `extreme_assertions`).

docs/userguide/src/portingguide/debugging/prefix.md

@@ -0,0 +1,10 @@
+# Debugging Tips
+
+In this section, we discuss debugging tips that will be useful to debug MMTk
+in a binding implementation. We will focus on discussing strategies and tools
+in the specific context of debugging MMTk.
+
+We aim to enhance the debugging capabilities for MMTk. However, as of October 2023, our debugging
+tools remain limited. We welcome your feedback and suggestions. If there's a specific debugging tool
+you'd like to see or have recommendations, please reach out to us on [Zulip](https://mmtk.zulipchat.com/)
+or submit your thoughts via [issues](https://github.com/mmtk/mmtk-core/issues).