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Patching Smali Files

A92·Sep 3, 2026·Source: Web

Markdown
---
name: patching-smali-files
description: Reads, analyzes, modifies, and validates Android .smali files against a natural-language patch instruction, producing error-free patched smali with full round-trip validation, a detailed patch report, and metadata. Use when the user uploads .smali files and asks to inject code, force a return value, bypass a check, remove logic, or otherwise modify decompiled Android bytecode. Never delivers patched output if any validation error or warning exists.
---

Quick Start14 / 15

Upload one or more .smali files and describe the patch (e.g. "force isPremium() to always return true"). The skill analyzes the target method, generates a register-safe patch, round-trips it through the assembler/disassembler for validation, and returns patched_output.zip (patched files + originals + report + logs) — only if validation passes with 0 errors and 0 warnings. On failure, only the report and logs are returned, never the ZIP.

Recommendation▾

Add a brief negative/failure example showing what a FAILED report and remediation_steps section looks like in practice

Inputs & Outputs

Inputs:

smali_files (required) — one or more .smali files
patch_instruction (required) — natural language description of the desired change
preferred_style (optional, default minimal) — minimal (no comments) or verbose (inline comments)
max_attempts (optional, default 5) — retry budget for validation fixes
allow_creative_solution (optional, default true) — if false, pause on any ambiguity instead of choosing

Outputs:

patched_output.zip — delivered ONLY on PASSED: /patched/, /originals/, patch_report.txt, metadata.json, validation_logs/
patch_report.txt — always delivered
metadata.json — always delivered
validation_logs/ — always delivered

Acceptance Criteria

Round-trip (smali → dex → baksmali → smali → dex) MUST yield 0 errors and 0 warnings, or nothing is delivered except report+logs.
Only requested files/methods are modified; any extra change is explicitly justified in the report.
patch_report.txt includes before/after snippets, reasoning, assumptions, and validation summary for every touched method.
Originals preserved verbatim under /originals/.
metadata.json includes SHA-256 checksums for originals, patched files, and the final ZIP.

Hard Constraints

MUST update .locals whenever new registers are introduced.
MUST NOT deliver patched_output.zip if any error/warning exists anywhere in validation logs.
MUST NOT reuse a register that is live or needed later on any control path.
MUST NOT insert instructions after an executed return/throw on the same path (no dead code injection unless explicitly retained as documented unreachable code).
MUST NOT circumvent DRM, licensing, or violate applicable law — refuse instead.
MUST log exact tool versions and exact shell commands verbatim per step.
MUST NOT modify method signatures, class headers, or field declarations unless explicitly required by the instruction.
MUST preserve existing exception handlers unless explicitly targeted.
MUST prefix injected labels uniquely: :patch_<job_id>_<n>.
MUST document every assumption when the instruction is ambiguous or underspecified.

Workflow15 / 15

Progress:

Step 1: Parse & normalize instruction
Step 2: Pre-check & setup (checksums, toolchain versions, working copies)
Step 3: Static analysis (CFG, registers, exception ranges, insertion point)
Step 4: Generate & insert patch
Step 5: Round-trip validation (mandatory, with retry loop)
Step 6: Smoke tests (if provided)
Step 7: Package output + write report/metadata
Step 8: Deliver (ZIP only if PASSED)

Step 1 — Parse & Normalize

Map instruction verbs to canonical ops: inject, replace, remove, change-return, add-hook, replace-conditional. Classify ambiguity:

LOW — single unambiguous target → proceed.
MEDIUM — multiple candidates or unclear insertion point → if allow_creative_solution=true, pick using the candidate resolution priority (exact descriptor match > visibility > param similarity > file order) and document; else pause and ask.
HIGH — sweeping language ("remove all checks", "disable everything") → ALWAYS pause for explicit confirmation, regardless of allow_creative_solution.

If a clause maps to zero methods, report as NO-OP and list available signatures.

Step 2 — Pre-check & Setup

Compute SHA-256 for every input file; verify it parses (.class header + matched .method/.end method).
Log tool versions: smali --version, baksmali --version, java -version → validation_logs/00_toolchain.log.
Copy originals verbatim to /originals/; all edits happen on working copies only.

Step 3 — Static Analysis

Extract class header, fields, method signatures.
For each target method: current .locals, full register map, CFG with basic blocks/branches/returns, exception handler ranges, and live-register set at each candidate insertion point (forward data-flow: a register is live if read on some path before being overwritten).
Determine exact insertion point per action type (inject-at-start, inject-before-return[s], replace, replace-conditional) and document it.

Step 4 — Patch Generation & Insertion

Generate snippet per preferred_style.
Compute new registers needed; increment .locals by exactly that amount, allocating from the highest unused index downward to avoid clobbering live/parameter registers.
Insert at the determined point, matching indentation, with unique :patch_<job_id>_<n> labels.
Run static sanity checks before assembling: label uniqueness/resolution, valid type descriptors, .locals ≥ max register used, no post-return instructions on the same path. Auto-correct failures before proceeding.

Step 5 — Round-Trip Validation (MANDATORY)

smali assemble -o patched.dex patched_smali/ → 01_assemble.log
baksmali disassemble -o roundtrip_smali/ patched.dex → 02_disassemble.log
smali assemble -o roundtrip.dex roundtrip_smali/ → 03_reassemble.log
Diff patched regions only (patched_smali/ vs roundtrip_smali/), ignoring cosmetic normalization → 04_diff.log
On any error/warning: diagnose (see Troubleshooting), auto-fix, increment attempt counter, re-run 1–4. Log each attempt as attempt_<N>_*.log. If max_attempts reached without a clean pass → mark FAILED, skip to Step 7 (report/logs only).

Step 6 — Smoke Tests (if applicable)

Run any user-supplied tests/verifier against the patched dex. Log to 05_smoke_tests.log / 06_verifier.log. Failures here are flagged as WARNING in the report but do not block delivery on their own (only round-trip errors/warnings block delivery).

Step 7 — Packaging & Reporting

Build the ZIP structure exactly as specified in Outputs. Generate patch_report.txt (see Report Template) and metadata.json with job id, timestamp, status, tool versions, per-file checksums/methods/line deltas, zip checksum, attempt count, and allow_creative_solution.

Step 8 — Delivery

PASSED → deliver ZIP + report + metadata.
FAILED → deliver report + metadata + logs only, never the ZIP. Report MUST include a numbered remediation_steps section and the last unvalidated patched file labeled UNVALIDATED — DO NOT USE IN PRODUCTION.

Recommendation▾

Consider trimming the Hard Constraints section slightly by grouping related rules, as it's dense even if thorough

Examples18 / 20

Example 1 — Inject at method start Input: "inject a write to debug_log.txt at the start of onCreate" on Lcom/example/MyActivity;->onCreate(Landroid/os/Bundle;)V Output: .locals raised 2→5, try/catch-wrapped FileWriter write inserted after the locals directive and before invoke-super, unique :patch_abc123_* labels, PASSED after 1 attempt. Assumptions logged: external storage permission assumed present; IOException swallowed silently.

Example 2 — Force return value Input: "force isPremium() to always return true" Output: Entire method body replaced with const/4 v0, 0x1 / return v0; .locals reduced 4→1; original validation call removed and documented as an explicit, intentional deletion. PASSED after 1 attempt.

Example 3 — Bypass conditional check Input: "bypass license check in checkLicense(Ljava/lang/String;)Z" Output: if-eqz v0, :cond_fail branch removed, unconditional return v1 (true) inserted; :cond_fail block retained as documented dead code to avoid dangling label references. PASSED after 1 attempt.

Example 4 — Remove a guard (risk-flagged) Input: "remove the null check at the top of processData(Ljava/lang/Object;)V" Output: if-eqz p1, :cond_null removed; :cond_null retained as dead code; report flags MEDIUM runtime NPE risk and states the user is responsible for call-site safety. PASSED after 1 attempt.

Recommendation▾

Include a small example of metadata.json or patch_report.txt structure to make the output format fully concrete

Best Practices

Always run the full LOW/MEDIUM/HIGH ambiguity check before touching any file — HIGH-risk phrasing always requires confirmation, no exceptions.
Allocate new registers from the top down; never touch a register proven live by data-flow analysis.
Keep diffs minimal — the report must justify every line changed beyond the literal instruction.
Treat round-trip validation as non-negotiable: it is the sole gate for ZIP delivery, independent of how "obviously correct" a patch looks.
Retain unreachable code (e.g., orphaned :cond_fail blocks) instead of deleting it when other references might exist — safer than risking a dangling label.

Common Pitfalls

Forgetting to bump .locals after adding registers → Verifier error: .locals count too low.
Reusing a live register for injected temporaries → corrupts unrelated program state.
Inserting code after a return/throw without a reachable label/goto → dead code / unreachable instruction errors.
Colliding injected label names with existing ones → Duplicate label errors.
Treating baksmali's cosmetic re-formatting as a real diff mismatch — compare opcodes/registers, not whitespace.
Delivering the ZIP "because it looks fine" without completing the full 4-log round-trip — never skip validation steps 5.1–5.4.
Silently resolving HIGH-risk ambiguous instructions ("remove all checks") instead of pausing for confirmation.