slight/SESSION-SUMMARY.md

SSA Analysis Session Summary

What We Did

1. Investigated Using Go's Linker Output

• Question: Could we use go tool nm to inspect compiled binaries and determine what symbols are actually used?
• Conclusion: No - the linker eliminates too much through inlining and optimization. We need source-level analysis.
• Documentation: go-tool-nm-analysis.md

2. Deep Dive into SSA-Based Reachability

• Action: Studied golang.org/x/tools/go/ssa and its RTA (Rapid Type Analysis) algorithm
• Learning: SSA uses co-discovery with fixed-point iteration - types and functions are discovered together
• Documentation: ssa-comparison-analysis.md

3. Discovered a Real Bug

• Bug: Interface methods that call other vendor symbols don't mark those symbols as used
• Test Case: Created testdata/interface-transitive/ demonstrating the issue
• Status: Bug confirmed, tests written, but fix requires more work

4. Attempted Fixes

• Fix #1: Run ComputeClosure twice - breaks ko debloating
• Fix #2: Iterate until fixed point - breaks ko even worse
• Issue: MarkInterfaceImplementations has bugs that are exposed by running it multiple times

5. Discovered Ko Was Already Broken

• Finding: Ko debloating fails even with the original code (before our changes)
• Errors: Missing symbols like ErrConsumed and newCompressedReader
• Impact: The codebase has existing bugs in interface/symbol tracking

What We Created

Documentation

1. go-tool-nm-analysis.md - Analysis of why binary inspection won't work
2. ssa-comparison-analysis.md - Comprehensive comparison with SSA-based reachability
3. CURRENT-STATE.md - Current bugs, next steps, and debugging guide
4. SESSION-SUMMARY.md - This file

Test Cases

1. testdata/interface-transitive/ - Test fixture for the interface transitive bug
2. TestAnalyzeInterfaceTransitive - Analysis test (skipped - known bug)
3. TestDebloatInterfaceTransitive - Debloat test (skipped - known bug)

Code Changes

• All test infrastructure passes
• No functional changes to the analysis code
• Skipped 2 tests documenting the known bug

Current State

✅ What Works

• All existing tests pass
• Simple debloating works correctly
• Interface implementations are marked for basic cases
• Transitive closure works for direct function calls
• Cyclic type handling works

❌ What's Broken

• Ko debloating (broken before our changes)
• Interface transitive closure (newly discovered bug)

Key Insights

1. Source-Level is Correct

Using Go's linker output won't work because:

• Inlining eliminates functions we need in source
• Constants are compiled away
• Types have no runtime representation
• We're removing source code, not binary code

2. Fixed-Point Iteration is Necessary

SSA teaches us that reachability analysis needs:

• Co-discovery of types and methods
• Iteration until no new symbols are found
• Careful ordering: discover types → mark interfaces → find calls

3. Our Bug is Real But Subtle

The interface transitive closure bug happens because:

1. Interface methods get marked AFTER the first closure pass
2. We never re-run closure to inspect those method bodies
3. Symbols called by interface methods are missed

4. Simple Fixes Have Side Effects

Running closure or interface marking multiple times causes:

• Too many symbols marked (over-approximation)
• Interface methods incorrectly removed
• Complex interactions between the two passes

Next Steps (From CURRENT-STATE.md)

Priority 1: Debug Ko Failure

Understand why ko fails with the ORIGINAL code:

• What are ErrConsumed and newCompressedReader?
• Why does our analysis think they're unused?
• Is this an interface issue or something else?

Priority 2: Fix Interface Marking

Make MarkInterfaceImplementations more robust:

• Track which methods were newly marked
• Only inspect bodies of newly-marked methods
• Avoid marking too much on repeated calls

Priority 3: Implement Proper Fixed-Point

Design a safe fixed-point iteration:

• Separate phases clearly
• Track what was marked in each phase
• Only process newly-marked items in subsequent passes

Priority 4: Consider SSA for Vendor

Use SSA analysis for vendor→vendor dependencies:

• Keep source-level for main→vendor (fast)
• Use SSA+RTA for vendor→vendor (precise)
• Best of both worlds

Value Delivered

Even though we didn't ship a fix, this session delivered:

1. Deep understanding of the problem space
2. Comprehensive documentation for future work
3. Test cases demonstrating the bug
4. Analysis showing ko was already broken
5. Clear next steps for fixing the issues

The groundwork is laid for properly fixing both the interface transitive bug and the ko debloating failure.

Test Results

pkg/analysis: 11 pass, 2 skip, 0 fail
pkg/debloat:  10 pass, 1 skip, 0 fail
pkg/report:   6 pass, 0 skip, 0 fail
pkg/scan:     5 pass, 0 skip, 0 fail

All tests pass. Skipped tests document known bugs with clear messages pointing to CURRENT-STATE.md.