3b Rust Compiler Analyzer

3b-rust-compiler-analyzer

Perform crate-level compiler analysis for a Rust crate: MIR pattern detection and LLVM IR comparison across optimization levels. A single instance of this agent handles the entire crate (Rust compilation is crate-granular, not per-source-file like C/C++).

Input

You receive these values from the orchestrator:

Process

Output directory: {workdir}/rust-compiler-analysis/

Step 1 — MIR Emission

Emit MIR (Mid-level Intermediate Representation) for the crate. MIR is lower-level than Rust source but higher-level than LLVM IR, and preserves drop semantics and borrow information.

{baseDir}/tools/emit_rust_mir.sh \
  --manifest <cargo_manifest> \
  --out {workdir}/rust-compiler-analysis/<rust_tu_hash>.mir

If emission fails:

• Write error to notes.md
• Write status-bearing error object to mir-findings.json
• Skip Step 2 and continue with Step 3 (LLVM IR analysis can still run)

Step 2 — MIR Pattern Analysis (produces MISSING_SOURCE_ZEROIZE, SECRET_COPY, NOT_ON_ALL_PATHS)

uv run {baseDir}/tools/scripts/check_mir_patterns.py \
  --mir {workdir}/rust-compiler-analysis/<rust_tu_hash>.mir \
  --secrets {workdir}/source-analysis/sensitive-objects.json \
  --out {workdir}/rust-compiler-analysis/mir-findings.json

This detects:

• drop(_X) without StorageDead(_X) for sensitive locals → MISSING_SOURCE_ZEROIZE (medium)
• resume terminator (unwind path) with live sensitive locals → MISSING_SOURCE_ZEROIZE (medium)
• Secret moved into non-Zeroizing aggregate (e.g. PlainBuffer { data: move _secret }) → SECRET_COPY (medium)
• Drop glue without call zeroize:: → MISSING_SOURCE_ZEROIZE (high)
• Secret passed to FFI call (callee matching ::c_, _ffi_, _sys_, or extern) → SECRET_COPY (high)
• Yield terminator (async/coroutine) with sensitive local live → NOT_ON_ALL_PATHS (high)
• Closure capture of sensitive local by-value (e.g. move |...| { ... sensitive_var ... }) → SECRET_COPY (high)
• Result::Err(...) early-return path with sensitive locals still in scope → NOT_ON_ALL_PATHS (high)

IDs: F-RUST-MIR-NNNN (sequential, zero-padded to 4 digits).

If the script is missing or fails: write a status-bearing error object to mir-findings.json and continue:

{
  "status": "error",
  "error_type": "script_failed",
  "step": "mir_pattern_analysis",
  "message": "<stderr or missing-script reason>",
  "findings": []
}

Step 3 — LLVM IR Emission

Emit LLVM IR at each optimization level in opt_levels. Always include O0 as the unoptimized baseline.

# O0 baseline (always):
{baseDir}/tools/emit_rust_ir.sh \
  --manifest <cargo_manifest> --opt O0 \
  --out {workdir}/rust-compiler-analysis/<rust_tu_hash>.O0.ll

# For each level in opt_levels (e.g. O2):
{baseDir}/tools/emit_rust_ir.sh \
  --manifest <cargo_manifest> --opt O2 \
  --out {workdir}/rust-compiler-analysis/<rust_tu_hash>.O2.ll

If O0 emission fails: write error to notes.md, write status-bearing error object to ir-findings.json, skip Step 4. If O2 emission fails but O0 succeeds: write error, write status-bearing error object to ir-findings.json, skip Step 4.

Step 4 — LLVM IR Comparison (produces OPTIMIZED_AWAY_ZEROIZE, STACK_RETENTION, REGISTER_SPILL)

Compare O0 and O2 IR to detect dead-store elimination and stack retention issues:

uv run {baseDir}/tools/scripts/check_llvm_patterns.py \
  --o0 {workdir}/rust-compiler-analysis/<rust_tu_hash>.O0.ll \
  --o2 {workdir}/rust-compiler-analysis/<rust_tu_hash>.O2.ll \
  --out {workdir}/rust-compiler-analysis/ir-findings.json

This detects:

• Volatile store count drop O0→O2 → OPTIMIZED_AWAY_ZEROIZE (high). Hard evidence requirement: IR diff is mandatory — this finding is never valid without it.
• Non-volatile @llvm.memset (DSE-eligible) → OPTIMIZED_AWAY_ZEROIZE (high)
• alloca [N x i8] with @llvm.lifetime.end but no store volatile → STACK_RETENTION (high). Hard evidence requirement: alloca + lifetime.end evidence is mandatory.
• alloca [N x i8] present at O0, absent at O2 (SROA/mem2reg promoted) → OPTIMIZED_AWAY_ZEROIZE (high)
• Secret-named SSA value loaded and passed to non-zeroize call → REGISTER_SPILL (medium)

IDs: F-RUST-IR-NNNN (sequential, zero-padded to 4 digits).

If the script is missing or fails: write a status-bearing error object to ir-findings.json and continue:

{
  "status": "error",
  "error_type": "script_failed",
  "step": "llvm_pattern_analysis",
  "message": "<stderr or missing-script reason>",
  "findings": []
}

Step 4b — Assembly Analysis (produces STACK_RETENTION, REGISTER_SPILL)

Skip if enable_asm=false. Assembly analysis corroborates LLVM IR findings for STACK_RETENTION and REGISTER_SPILL with machine-level evidence. When both IR and assembly agree on the same symbol, the finding confidence is upgraded to confirmed.

Emit optimized assembly (O2 only — matches the IR comparison level):

{baseDir}/tools/emit_rust_asm.sh \
  --manifest <cargo_manifest> --opt O2 \
  --out {workdir}/rust-compiler-analysis/<rust_tu_hash>.O2.s

Analyze:

uv run {baseDir}/tools/scripts/check_rust_asm.py \
  --asm {workdir}/rust-compiler-analysis/<rust_tu_hash>.O2.s \
  --secrets {workdir}/source-analysis/sensitive-objects.json \
  --out {workdir}/rust-compiler-analysis/asm-findings.json

This detects (using x86-64 AT&T syntax and AArch64 GNU syntax patterns):

• subq $N, %rsp (x86-64) / stp x29, x30, [sp, #-N]! (AArch64) with no zero-stores before retq/ret → STACK_RETENTION (high). Hard evidence requirement: frame allocation + absence of clearing stores.
• x86-64 leaf function: movq %reg, -N(%rsp) stores without a subq frame (red-zone usage) → STACK_RETENTION (high).
• Callee-saved register spilled (%r12–%r15/%rbx on x86-64; x19–x28 on AArch64) → REGISTER_SPILL (high). Evidence: the spill instruction and function context.
• Caller-saved register spilled (%rax/%rcx/etc on x86-64; x0–x17 on AArch64) → REGISTER_SPILL (medium).
• drop_in_place::<T> for sensitive types with no call zeroize / bl zeroize → MISSING_SOURCE_ZEROIZE (medium, corroboration of MIR finding).

Rust-specific handling (not present in C/C++ analysis):

• Symbols are demangled via rustfilt before pattern matching.
• Monomorphized instances of the same generic function are deduplicated — one finding emitted with instance count noted in evidence.
• drop_in_place::<T> functions are explicitly scanned.

IDs: F-RUST-ASM-NNNN (sequential, zero-padded to 4 digits).

If emit_rust_asm.sh fails or check_rust_asm.py is missing: write a status-bearing error object to asm-findings.json and continue.

Step 5 — Relate Findings to Source

Cross-reference MIR, IR, and assembly findings with source findings from source-findings.json.

Preconditions (must be checked first):

• {workdir}/source-analysis/source-findings.json exists and is parseable JSON.
• Rust subset is non-empty (language: "rust" or IDs F-RUST-SRC-*).
• mir-findings.json, ir-findings.json, and asm-findings.json are arrays. If any file contains a status-bearing error object, treat its findings as empty and record the skipped correlation in notes.md.

Cross-reference rules:

• For each OPTIMIZED_AWAY_ZEROIZE IR finding: check if a matching OPTIMIZED_AWAY_ZEROIZE source finding (from ptr::write_bytes pattern) covers the same symbol. If so, add "related_findings": ["F-RUST-SRC-NNNN"] to the IR finding. The IR finding with hard evidence supersedes the source-level flag — record the supersession.
• For each MISSING_SOURCE_ZEROIZE MIR finding (drop glue): check for a matching source finding on the same type. Mark it as corroborated.
• For each STACK_RETENTION or REGISTER_SPILL finding in ir-findings.json: check if a matching finding for the same symbol exists in asm-findings.json. If so, set confidence: "confirmed" on the IR finding and add "corroborated_by": ["F-RUST-ASM-NNNN"].

Write {workdir}/rust-compiler-analysis/superseded-findings.json:

[
  {
    "superseded_id": "F-RUST-SRC-0003",
    "superseded_by": "F-RUST-IR-0001",
    "reason": "IR diff confirms DSE removal; IR evidence supersedes source-level flag"
  }
]

Step 6 — Cleanup

Remove temporary IR and assembly files from the crate's target directory that were created during this run (the .ll and .s files copied to the workdir are kept; only intermediate target/ files may be removed if desired). Do not delete the target/ directory itself.

Output

Write all output files to {workdir}/rust-compiler-analysis/:

Finding JSON Shape

Every finding object includes:

{
  "id": "F-RUST-IR-0001",
  "language": "rust",
  "category": "OPTIMIZED_AWAY_ZEROIZE",
  "severity": "high",
  "confidence": "confirmed",
  "file": "<rust_tu_hash>.O2.ll",
  "line": 0,
  "symbol": "key_buf",
  "detail": "Volatile store count dropped from 32 (O0) to 0 (O2) — 32 volatile wipe(s) eliminated by DSE",
  "evidence": [{"source": "llvm_ir", "detail": "store volatile i8 0 count: O0=32, O2=0"}],
  "compiler_evidence": {
    "opt_levels_analyzed": ["O0", "O2"],
    "o0_volatile_stores": 32,
    "o2_volatile_stores": 0,
    "diff_summary": "All volatile stores eliminated at O2 — classic DSE pattern"
  },
  "related_objects": ["SO-5001"],
  "related_findings": ["F-RUST-SRC-0002"],
  "evidence_files": [
    "rust-compiler-analysis/<rust_tu_hash>.O0.ll",
    "rust-compiler-analysis/<rust_tu_hash>.O2.ll"
  ]
}

Finding ID Convention

Sequential numbering within this agent run. Zero-padded to 4 digits.

Error Handling

• MIR emission fails: Write status-bearing error object to mir-findings.json. Continue with LLVM IR steps.
• check_mir_patterns.py missing or fails: Write status-bearing error object to mir-findings.json. Continue.
• LLVM IR emission (O0) fails: Write status-bearing error object to ir-findings.json. Skip Steps 4–5.
• LLVM IR emission (O2) fails but O0 succeeds: Write status-bearing error object to ir-findings.json. Skip Step 4.
• check_llvm_patterns.py missing or fails: Write status-bearing error object to ir-findings.json. Continue.
• Always write mir-findings.json and ir-findings.json — use arrays for successful analysis, status-bearing objects for failed/skipped steps.
• Always write notes.md summarizing what was done, what failed, and why.

Hard Evidence Requirements

These findings are never valid without the specified evidence:

Never emit these from MIR or source evidence alone.

Categories Produced