Month: 2025-10 — Focused delivery and reliability hardening across the OpenXiangShan codebase, with notable cross-repo integration to align the DiffTest framework with XiangShanSim. Delivered core feature upgrades, stabilized CI, and improved top-level simulation design to boost developer productivity and confidence in hardware verification results.

September 2025: Delivered targeted performance, coverage, and build-system enhancements across OpenXiangShan repositories, delivering measurable business value through improved observability, CI reliability, and scalable RTL integration. Key momentum in code-quality tooling, coverage workflows, and memory model capabilities, complemented by stability fixes for Verilator compatibility and tool-path handling.

August 2025 monthly summary highlighting key features and stability improvements across OpenXiangShan/difftest and OpenXiangShan/circt. Implemented CI optimization using pre-built libfuzzer.a to speed CI builds; added FIRRTL branch-coverage instrumentation; automated firtool release process across multiple OSes, streamlining builds, tests, and releases. Impact: reduced CI build times, enhanced hardware-coverage visibility, and increased release reliability. Demonstrated skills in CI/CD optimization, tooling automation, FIRRTL transformations, and cross-OS release engineering.

July 2025 Monthly Summary This month focused on CI reliability, standardized tooling, and build flexibility across the OpenXiangShan codebase, with targeted enhancements in the difftest testing framework and XiangShan build processes. The work improved test coverage, reduced runtime overhead, and provided clearer interfaces for future integrations. Key features delivered - CI improvements: Unified Docker image references to the xs-env repository and expanded GSIM test coverage across CI pipelines (commits 86c69dc6ea2834d81b929b0efe33f3c4b24d0479; 09c581f40ea774bdc31564c2892b63618a637f14). - Standardized file naming: Introduced create_noop_filename utility to standardize output filenames (waveforms, snapshots, coverage) and refactored code for consistency (commit b0cb62de028ca5bcacd7d062bd9e842dacc074de). - Waveform tracing improvements: Refactored tracing with EmuWaveform class and gated tracing behind VM_TRACE to reduce overhead (commit 105756a7b009dfa241d8fd705e218021b57ac66f). - RTL simulators abstraction: Added an abstraction layer for RTL simulators in emu-mode to standardize interfaces and simplify DiffTest integration (commit def17e3d9212f3056d5368592c7ad52594767068). - XiangShan build flexibility: Refactor Makefile to apply --split-verilog only when CHISEL_TARGET=systemverilog and add support for configurable FIRTOOL binary path, improving targeted Verilog generation and build flexibility (commit 95d4f4a07bdc781a0c6d4bee570649b913629037). Major bugs fixed - Memory management bug in update_is_feedback: Correct allocation/deallocation using new[]/delete[] to address clang warning and prevent potential leaks, ensuring robust memory handling in correctness checks (commit 6af13d93fa6fc85fbb092406d8b118de67fe8740). Overall impact and accomplishments - Increased CI reliability and test coverage across the OpenXiangShan repos, reducing risk in deployment pipelines and accelerating feedback loops. - Improved maintainability and consistency through standardized naming, deterministic waveform/coverage outputs, and a unified emulator interface. - Enhanced build flexibility for SystemVerilog workflows and custom tool paths, enabling targeted Verilog generation and smoother integration into new verification flows. Technologies and skills demonstrated - C/C++ memory management, dynamic allocation patterns, and compiler warning mitigation. - CI/CD process improvements, Docker image management, and test strategy expansion (GSIM integration). - Build system optimization (Makefile logic, CHISEL_TARGET/FIRTOOL handling) and configuration management. - Emulation tooling improvements (EmuWaveform, VM_TRACE gating) and modular abstractions for RTL simulators. - Cross-repo collaboration and integration of testing frameworks with the DiffTest ecosystem.

May 2025 monthly summary for OpenXiangShan/XiangShan-doc centered on documenting research outputs and improving traceability. Implemented a publication record entry for the XiangShan 2024 IEEE Hot Chips 36 Symposium with DOI and links; updated publications.md; reinforced repository documentation hygiene and visibility of key publications.

April 2025 monthly summary: Key feature deliveries and reliability improvements across OpenXiangShan/difftest and OpenXiangShan/XiangShan. Difftest CI/CD environment standardized by migrating to OpenXiangShan Docker images for cross-Ubuntu testing, removing redundant environment setup, and pre-installing the Rust toolchain before fuzz tests to prevent nightly regressions. Difftest instruction display refactor replaced the vector-based circular queue with a native C++ queue, simplifying data flow and potential performance gains. XiangShan fuzz testing configuration updated to KunminghuV2 to enhance test reliability and coverage. These changes collectively improve build stability, reduce flaky tests, and accelerate feedback loops for developers. Demonstrated proficiency in Dockerized CI, C++ data handling, Rust toolchain management, and fuzz configuration practices.

March 2025: OpenXiangShan/difftest focused on strengthening the toolchain by upgrading the Chisel dependency to 6.7.0 to ensure MLIR FIRRTL compatibility and to leverage newer compiler features. This included updating README.md and build scripts to reflect the upgrade. No critical bugs were identified or fixed this month; the work delivered improvements in compatibility, maintainability, and readiness for future MLIR FIRRTL workflows. Commit 4759cebc49f83c035385fdb5438b06174a1c4972 (Bump Chisel 6.7.0 (#596)) documents the change. Business value: smoother CI/CD, reduced risk from outdated tooling, and improved developer velocity for downstream features.

February 2025 monthly summary for OpenXiangShan/difftest focused on quality and noise reduction in issue tracking. Delivered a targeted bug fix to disable blank GitHub issue creation, ensuring submitted issues contain meaningful content and reducing support overhead. The change is implemented via the blank_issues_enabled flag set to false, tied to commit e710bf07feeae1908e32cfd7fccef2e8006d5a49 (github: disable blank issues) and aligns with issue #577.

January 2025 monthly summary for OpenXiangShan projects focused on improving CI/build reliability for libdifftest, expanding DiffTest resources, and adding hardware verification presentation materials. Key outcomes include a robust Libdifftest CI/build flow for XiangShan with proper RTL header inclusion, CI validation of libdifftest.so, suppression of Verilator noise when it is not installed, and corrected artifact upload paths. Documentation expanded with DiffTest resources and guidance on integrating DiffTest with coverage-guided fuzzing. Hardware verification tooling slides were added to XiangShan-doc to aid knowledge transfer, training, and stakeholder communications. Major improvements were accompanied by targeted fixes: (1) fix(libso): include headers from RTL simulators, eliminating missing-header errors; (2) fix(ci): correct path for libdifftest.so, ensuring reliable artifact collection; (3) avoid error messages for non-Verilator environments, reducing CI noise. These changes collectively improve CI stability, build reproducibility, and onboarding for contributors. Technologies/skills demonstrated include: CI/CD automation, build system tuning and header management, Verilator integration handling, artifact management, and documentation/slide creation, all contributing to faster delivery and better test coverage.

December 2024 highlights across OpenXiangShan/difftest and OpenXiangShan/riscv-isa-sim, focusing on robustness, test fidelity, and CI reliability to accelerate hardware/software validation and onboarding. Major work targeted core reliability in flash handling, richer diff-testing capabilities, and streamlined build/test workflows, delivering tangible business value through faster feedback cycles, reduced manual setup, and lower risk of flaky tests. Key features delivered and business value: - Flash image loading and initialization overhaul: introduced a new load_flash_bin_v2 API, unified flash initialization via a flash_device_t structure, and updated refproxy.cpp and difftest.cpp to the new initialization flow. This improves robustness and flexibility of flash handling across tests and reduces setup complexity for large designs. (Commits: 4660e7258b9beaedf5185d9b359e03e1edc8ef14; 0db57c1997b52af467af01a90fb2822abb6a53ef; 9f7766521e73544121246ceb337e5dc7021546ab; 4f4f2ee3f594e619026651875784b71ace8fb4bd) - Difftest: support recursive bundles: enhanced DifftestBundle parsing to handle recursive bundles, including nested bundles and vectors, aligning DPI-C and DifftestBundle behavior for more complex data structures. This expands test coverage for intricate hardware data flows. (Commit: bcc18062ad7a498f97bbfaedcdfa7a03e1e25b85) - CI/CD workflow improvements: moved fuzzing tests to a nightly schedule and simplified build commands to reduce noise and improve test stability across commits, enabling faster and more reliable feedback. (Commits: 794609064097328e5d5965c16057f4ec9d22344d; 8cfb9925e64b31ba94041895cbc624b4a9ceae11) - Wiring: propagate only visible data: restricted data propagation in wiring addSink to visible sources to avoid propagating invisible or pending data in hierarchical wiring scenarios, improving correctness and reducing side effects. (Commit: 47f87d513248fca289ba092dc48dc62ef6520c43) - Build system and performance tuning: streamlined builds and runtime performance by setting the default REF Proxy to Nemu and increasing the default LightSSS snapshot interval from 1s to 10s, reducing overhead for large designs while preserving observability. (Commits: 8a4a73eab5fb99d25c68077e891c8907c787d481; 235012ec8f4507a2df3952e857bbcec5448f2950)

November 2024 performance summary across OpenXiangShan/NEMU, OpenXiangShan/difftest, and OpenXiangShan/ChiselAIA. Focused on reliability, profiling capabilities, and developer productivity. Key outcomes include a critical bug fix in flash memory IO, a robust difftest profiling framework with public APIs and JSON export, IO/file-writing refactor for better maintainability, improved resilience when no CPU cores are connected, and tooling/documentation upgrades that align with modern Chisel/Mill versions.

October 2024 monthly summary for OpenXiangShan/NEMU. The focus this month was strengthening reliability, correctness, and build stability to support faster iteration and fewer regressions in development and testing environments. Key emulator correctness fixes, robust diff-testing workflows, and targeted build/init improvements collectively improved product quality and developer velocity.