Code Coverage with gcov
This Claude Code skill adds gcov instrumentation to C/C++ projects to measure test coverage. Use it when you need to analyze which lines of code are executed during testing, integrating the `--coverage` flag into Makefile or CMake build systems, then generating text or HTML reports showing line-by-line, branch, and function coverage metrics.
git clone --depth 1 https://github.com/deonmenezes/mantishack /tmp/code-coverage-with-gcov && cp -r /tmp/code-coverage-with-gcov/.claude/skills/crash-analysis/gcov-coverage ~/.claude/skills/code-coverage-with-gcovSKILL.md
# Code Coverage with gcov
## Purpose
Instrument C/C++ programs with gcov to measure test coverage.
## How It Works
### Build with Coverage
```bash
gcc --coverage -o program source.c
```
### Run Program
```bash
./program
# Creates .gcda files with execution data
```
### Generate Reports
**Text report:**
```bash
gcov source.c
# Creates source.c.gcov with line-by-line coverage
```
**HTML report:**
```bash
gcovr --html-details -o coverage.html
```
## Coverage Flags
- `--coverage` (shorthand for `-fprofile-arcs -ftest-coverage -lgcov`)
- Add to both `CFLAGS` and `LDFLAGS`
## Build System Integration
### Makefile
```makefile
ENABLE_COVERAGE ?= 0
ifeq ($(ENABLE_COVERAGE),1)
CFLAGS += --coverage
LDFLAGS += --coverage
endif
```
### CMake
```cmake
option(ENABLE_COVERAGE "Enable coverage" OFF)
if(ENABLE_COVERAGE)
add_compile_options(--coverage)
add_link_options(--coverage)
endif()
```
## When User Requests Coverage
### Steps
1. Detect build system (Makefile/CMake/other)
2. Add `--coverage` to CFLAGS and LDFLAGS
3. Clean previous build: `make clean` or `rm -f *.gcda *.gcno`
4. Build with coverage: `make ENABLE_COVERAGE=1` or `cmake -DENABLE_COVERAGE=ON`
5. Run tests: `make test` or `./test_suite`
6. Generate report: `gcovr --html-details coverage.html --print-summary`
7. Present summary and path to HTML report
## Output
**Text (.gcov files):**
```
-: 0:Source:main.c
5: 42: int x = 10;
#####: 43: unused_code();
```
- `5:` = executed 5 times
- `#####:` = not executed
- `-:` = non-executable
**HTML:** Interactive report with color-coded coverage
## Metrics
- **Line coverage**: Executed lines / total lines
- **Branch coverage**: Taken branches / total branches
- **Function coverage**: Called functions / total functions
Target: 80%+ line coverage, 70%+ branch coverageUse this agent when the target is a LIVE REST or GraphQL API you are authorized to test and the question is "can I tamper request bodies, headers, ids, and tokens to read or act on data that isn't mine?" — active, request-driven abuse of the API contract, not static code review. It drives REAL HTTP at the endpoints: BOLA/IDOR object-id enumeration (increment/swap/UUID-shuffle the id and diff the access decision), broken function-level authz (replay an admin verb/path with a low-priv token), mass-assignment (inject role/is_admin/is_verified/owner_id into the JSON body), excessive-data-exposure (the response over-returns fields the UI never shows), GraphQL introspection + alias/batch amplification + nested-query DoS, content-type and HTTP-verb tampering (POST→PUT/PATCH/DELETE, application/json→text/plain→x-www-form-urlencoded), JWT/session/token swap across two users, and rate-limit / idempotency-key bypass. It proves every finding with a behavioral oracle — a status/length/timing/field-set diff between the authorized baseline and the tampered request — never a guess. Prefer this agent over a code reader when you hold a base URL or a schema and want to mutate live traffic methodically.\n\n<example>\nContext: The user has a running API with numeric resource ids and two test accounts.\nuser: "Here's our staging API at https://api.staging.acme.test and tokens for user A and user B — can user A read user B's orders?"\nassistant: "That's textbook BOLA: same endpoint, swap the object id (or the bearer token) and diff the access decision. I'll use the Task tool to launch the api-abuse-fuzzer agent to enumerate /orders/{id} with A's token against B's ids and prove the cross-tenant read with a status + ownership-field oracle."\n<agent_launch>\nDelegating to api-abuse-fuzzer: a live authorized API + two tokens + object-id enumeration is its core BOLA/IDOR mission.\n</agent_launch>\n</example>\n\n<example>\nContext: The user exposes a GraphQL endpoint and isn't sure introspection or query batching is locked down.\nuser: "Our /graphql is behind auth but I want to know if a low-priv user can pull admin fields, brute force via aliases, or knock it over with a deep nested query."\nassistant: "GraphQL abuse surface: introspect the schema, alias-batch a login/lookup to bypass per-request rate limits, and send a bounded cyclic nested query as a timing oracle. I'll launch the api-abuse-fuzzer agent to tamper the operation and measure the depth/timing oracle."\n<agent_launch>\nDelegating to api-abuse-fuzzer for GraphQL introspection, alias/batch amplification, and nested-query DoS against the live endpoint.\n</agent_launch>\n</example>\n\nProactively suggest using this agent when: a live base URL + an OpenAPI/Swagger/GraphQL schema (or a captured request) is in hand and the target is authorized in-scope; endpoints take a resource identifier in the path/query/body (/users/{id}, ?account=, {"order_id": ...}) — BOLA/IDOR territory; the user holds 2+ accounts or tokens (low-priv + high-priv, tenant A + tenant B) to run an authorization differential; there are admin/privileged verbs (DELETE, PUT /admin/*, role-changing mutations) and you want to hit them as a non-admin; a write endpoint accepts a JSON object — test mass-assignment of role/is_admin/verified/balance/owner_id; a /graphql endpoint exists (introspection, alias/batch abuse, nested-query DoS, field-level authz); or the user mentions rate limiting, coupon/OTP brute force, idempotency keys, BOLA, BFLA, mass assignment, or "excessive data exposure".
Use this agent when a codebase, PR, or service needs its IMPLICIT TRUST ASSUMPTIONS enumerated and attacked — every place the code silently trusts a header, an "internal-only" route, an "already-validated-upstream" input, an ID that "belongs to the caller," or a value that "can't be null/negative." It specializes in confused-deputy (CWE-441), mass-assignment (CWE-915), input-validation gaps (CWE-20), and second-order/stored injection (CWE-89/CWE-79). This is the agent for trust-boundary audits, multi-service request paths, ORM/serializer review, and proxy/gateway/header-forwarding code.\n\n<example>\nContext: User has a multi-service backend where an edge proxy forwards auth context downstream.\nuser: "Our gateway sets X-User-Id from the JWT and the internal services read it to authorize. Can you check this?"\nassistant: "This is a classic confused-deputy / trust-boundary surface — the downstream services trust a header they can't verify. I'll use the Task tool to launch the assumption-pressure-test agent to enumerate every internal endpoint that reads X-User-Id and prove whether an attacker can reach it directly and forge it."\n<agent_launch>\nDelegating to assumption-pressure-test: the request hinges on an implicit 'this header is trusted because the gateway set it' assumption that must be attacked.\n</agent_launch>\n</example>\n\n<example>\nContext: User just merged an ORM update endpoint.\nuser: "Here's the new profile update handler: User.objects.filter(id=request.user.id).update(**request.data)"\nassistant: "That `**request.data` spread is a mass-assignment sink — it trusts that the request body only contains the fields you intended. I'll launch the assumption-pressure-test agent to map which model columns (is_admin, balance, role) become attacker-writable and confirm reachability."\n<agent_launch>\nDelegating to assumption-pressure-test for the CWE-915 mass-assignment and the implicit 'the body only has safe fields' assumption.\n</agent_launch>\n</example>\n\nProactively suggest using this agent when:\n- Code reads request headers (X-Forwarded-For, X-User-Id, X-Real-IP, X-Internal-*, Host) for trust or authorization decisions\n- A serializer/ORM uses bulk binding: `**req.body`, `Object.assign`, `ModelMapper`, `BeanUtils.copyProperties`, `update_attributes`, `params.permit!`\n- Comments or names assert trust: "internal only", "already validated", "trusted", "comes from gateway", "sanitized upstream"\n- Data is stored then later concatenated into SQL/HTML/shell (second-order injection)\n- An endpoint takes an `id`/`uuid`/`account`/`order` param that maps to a resource (IDOR / object ownership)
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