C/C++ Incremental Build Converter Skill

This skill converts C/C++ project build.sh and test.sh scripts to support incremental builds after docker commit.

CRITICAL CONSTRAINTS

1. DO NOT Modify oss-fuzz Infrastructure Code

NEVER modify these files:

• oss-fuzz/infra/helper.py

• oss-fuzz/infra/base-images/*

• Any other oss-fuzz infrastructure code

ONLY modify:

• oss-fuzz/projects/{project}/build.sh

• oss-fuzz/projects/{project}/test.sh

• oss-fuzz/projects/{project}/Dockerfile

  (if absolutely necessary)

2. If oss-crs Test Framework Has Issues

If the incremental build test framework (

incremental_build_checker.py

1. Report the issue to the user with clear explanation
2. Suggest a fix for the framework code
3. DO NOT implement the fix yourself - let the user decide

Example report format:

## oss-crs Framework Issue Detected

**File:** bug_fixing/src/oss_patch/inc_build_checker/incremental_build_checker.py
**Issue:** The source copy command destroys build artifacts
**Current behavior:** `rm -rf $SRC/nginx && cp -r ...`
**Expected behavior:** Should preserve objs/ directory
**Suggested fix:** Use rsync with --exclude objs instead of rm+cp

Key Architecture: Separate $SRC for build.sh and test.sh

IMPORTANT: $SRC is different between build.sh and test.sh.

• build.sh runs in

  /built-src

  →

  $SRC

  =

  /built-src

• test.sh runs in

  /test-src

  →

  $SRC

  =

  /test-src

These are completely separate directories. This separation means:

1. NO artifact cleanup needed - Don't delete .o, .lo, .a, .la, .libs
2. NO out-of-tree build needed - In-source build is fine since $SRC is separate
3. NO ASAN conflict - test.sh builds in its own clean copy

ALWAYS Use $SRC, NEVER Hardcode Paths

CRITICAL: Always use

$SRC

/src

/built-src

/test-src

# BAD - Hardcoded path breaks when $SRC changes
cd /src/project
cp -r /src/oniguruma modules/

# GOOD - Uses $SRC variable
cd $SRC/project
cp -r $SRC/oniguruma modules/

AVOID $WORK - Use $SRC Subdirectories for All Build Artifacts

CRITICAL: Avoid using $WORK for build-related directories. Use $SRC subdirectories instead.

$WORK

1. ASAN-instrumented libraries from build.sh conflict with test.sh
2. CMake paths recorded in $WORK become invalid when $SRC changes
3. Build artifacts from different environments can corrupt each other

Always use

$SRC

• Build directories (out-of-source builds)
• Install prefixes (for cmake/configure --prefix)
• Dependency installations

# BAD - Uses $WORK which is shared
BUILD_DIR="$WORK/build"
cmake "$SRC/project" -DCMAKE_INSTALL_PREFIX=$WORK

# GOOD - Uses $SRC subdirectories
BUILD_DIR="$SRC/project_build"
INSTALL_DIR="$SRC/project_install"
mkdir -p "$BUILD_DIR" "$INSTALL_DIR"
cd "$BUILD_DIR"
cmake "$SRC/project" -DCMAKE_INSTALL_PREFIX="$INSTALL_DIR"

In test.sh, also use $SRC subdirectories:

# BAD in test.sh - Uses shared $WORK with ASAN artifacts
./configure --prefix="$WORK"
# Error: undefined reference to __asan_*

# GOOD in test.sh - Uses separate prefix under $SRC
TEST_PREFIX="$SRC/test_deps"
mkdir -p "$TEST_PREFIX/lib" "$TEST_PREFIX/include"

if [ ! -f "$TEST_PREFIX/lib/libz.a" ]; then
    pushd "$SRC/zlib"
    ./configure --static --prefix="$TEST_PREFIX"
    make -j$(nproc) CFLAGS="-fPIC"  # No ASAN flags
    make install
    popd
fi

test.sh Does NOT Need Sanitizers - Disable Them Explicitly

IMPORTANT: test.sh runs unit tests, NOT fuzzing. Sanitizers are NOT needed and cause conflicts.

During incremental build testing, build.sh compiles with ASAN/sanitizer flags. When test.sh runs in the SAME directory, the object files from build.sh are ASAN-instrumented. If test.sh tries to link against these objects without ASAN runtime, you get undefined reference errors.

build.sh and test.sh Artifacts Should NOT Be Shared

CRITICAL: Build artifacts from build.sh should NOT be reused in test.sh.

During incremental build testing:

1. build.sh runs with ASAN flags → creates ASAN-instrumented

   .o

   files
2. test.sh runs in the SAME

   $SRC

   directory
3. If test.sh tries to use existing

   .o

   files, linking fails

The artifacts are incompatible because:

• build.sh: Compiles with

  -fsanitize=address -fsanitize-address-use-after-scope -fsanitize=fuzzer-no-link

• test.sh: Needs to link without sanitizer runtime

DO NOT use

|| true

Critical Requirements

1. Scripts MUST Work on BOTH First Run AND Repeated Runs

NEVER assume a script will only run once. Scripts must be idempotent.

# BAD - Runs configure every time
autoreconf -f -i
./configure

# GOOD - Only configure on first run
if [ ! -f Makefile ]; then
    autoreconf -f -i
    ./configure
fi
make -j$(nproc)

2. DO NOT Delete Build Artifacts

Since $SRC is separate, there's no need to clean artifacts. Deleting them defeats incremental build.

# BAD - Destroys incremental build benefits
find . -name "*.o" -delete
find . -name "*.a" -delete
rm -rf .libs

# GOOD - Just build, artifacts from previous run will speed things up
if [ ! -f Makefile ]; then
    ./configure
fi
make -j$(nproc)

3. Conditional Configure/Autoreconf

Only run configure-related commands on first execution.

# Pattern: Check for Makefile existence
if [ ! -f Makefile ]; then
    autoreconf -fi       # or ./bootstrap
    ./configure --options
fi
make -j$(nproc)
make check

4. Use

cp

Instead of

mv

mv

# BAD - Fails on second run
mv scripts/config.temp scripts/config

# GOOD - Preserves source file
[ -f scripts/config.temp ] && cp scripts/config.temp scripts/config || true

5. Use Guards for Dependencies

# Build dependency only if not already built
if [ ! -f "$WORK/lib/libz.a" ]; then
    pushd "$SRC/zlib"
    ./configure --static --prefix="$WORK"
    make -j$(nproc)
    make install
    popd
fi

6. Handle Failing Tests

Remove failing test files directly instead of using TESTS variable (which can propagate to submodules).

# BAD - TESTS variable propagates to submodules
make check TESTS="tests/mantest tests/jqtest"

# GOOD - Remove failing test files directly
rm -f tests/shtest
rm -f tests/multiple.*
sed -i '/multiple/d' tests/Makefile.am
make check

7. Copy Dependencies If Not Present (Conditional, Not Delete-and-Copy)

# BAD - Deletes and recopies every time, breaks incremental build
rm -rf modules/oniguruma
rsync -a $SRC/oniguruma modules/

# GOOD - Only copy if not present
if [ ! -d modules/oniguruma ]; then
    mkdir -p modules
    cp -r $SRC/oniguruma modules/
fi

8. Conditional Dict/Corpus File Copy

Files like dictionaries and seed corpus may not exist in all builds.

# BAD - Fails if file doesn't exist
cp $SRC/libtiff/contrib/oss-fuzz/tiff.dict $OUT/

# GOOD - Conditional copy with fallback
[ -f $SRC/libtiff/contrib/oss-fuzz/tiff.dict ] && cp $SRC/libtiff/contrib/oss-fuzz/tiff.dict $OUT/ || true
find . -name "*.tif" | xargs zip $OUT/seed_corpus.zip || true

9. Use

make -k check || true

for Potentially Failing Tests

Some tests may fail in fuzzing environment. Use

-k

|| true

# BAD - Stops on first test failure
make check

# GOOD - Continue through failures
make -k check || true

echo "Tests completed"

10. Remove Tests from Makefile.am BEFORE configure

When removing failing tests, modify Makefile.am BEFORE running autoreconf/configure.

# BAD - Removes test file but Makefile still references it
rm -f tests/shtest
autoreconf -fi
./configure
make check  # Error: No rule to make target 'tests/shtest'

# GOOD - Remove from Makefile.am before configure
sed -i 's| tests/shtest||g' Makefile.am
autoreconf -fi
./configure
make check  # Works

11. Rewrite Instead of Sourcing Internal build.sh

If the project's source contains its own build.sh (e.g.,

contrib/oss-fuzz/build.sh

mv

# BAD - Sources internal build.sh that uses mv
source $SRC/project/contrib/oss-fuzz/build.sh

# GOOD - Rewrite the logic with cp instead of mv
if [ ! -f "$WORK/lib/libjbig.a" ]; then
    pushd "$SRC/jbigkit"
    make lib
    # Use cp instead of mv for incremental build support
    cp "$SRC"/jbigkit/libjbig/*.a "$WORK/lib/"
    cp "$SRC"/jbigkit/libjbig/*.h "$WORK/include/"
    popd
fi

12. Guard

sed -i

Insertions with Pattern Checks

When using

sed -i

# BAD - Only checks if new content exists (can't distinguish original vs added)
if ! grep -q '%destructor' file.y; then
    sed -i '/^%%$/i%destructor { free ($$); } ID' file.y
fi

# GOOD - Check original pattern exists AND new content not yet added
if grep -q '^%%$' file.y && ! grep -q '%destructor' file.y; then
    sed -i '/^%%$/i%destructor { free ($$); } ID' file.y
fi

13. Guard Append Operations (

>>

)

Don't blindly use

>

>>

# BAD - Overwrites every time (inefficient, may lose state)
sed 's/main/old_main/' file.c > header.h

# BAD - Appends every time (file grows on each run)
sed 's/main/old_main/' file.c >> header.h

# GOOD - Only append if content not already present
if ! grep -q 'old_main' header.h 2>/dev/null; then
    sed 's/main/old_main/' file.c >> header.h
fi

14. CMake/Ninja Build Directory Must Use $SRC-Relative Path

When

$SRC

$WORK

# BAD - $WORK is shared, CMake source path mismatch causes ninja errors
BUILD_DIR="$WORK/build"
cd "$BUILD_DIR"
cmake $SRC/project  # Source path recorded as /built-src/project
# On test.sh: ninja fails because $SRC is now /test-src/project

# GOOD - Build directory relative to $SRC, each environment independent
BUILD_DIR="$SRC/project_build"
mkdir -p "$BUILD_DIR"
cd "$BUILD_DIR"
if [ ! -f build.ninja ]; then
    cmake -GNinja $SRC/project
fi
ninja

15. Disable ccache for Bazel Builds

Bazel has its own caching mechanism. ccache interferes with Bazel's compiler wrappers.

# BAD - ccache causes "invalid option" errors with Bazel
# Error: /usr/local/bin/ccache: invalid option -- 'U'
bazel build //...

# GOOD - Remove ccache from PATH before Bazel builds
export PATH=$(echo "$PATH" | sed 's|/ccache/bin:||g; s|:/ccache/bin||g')
unset CC CXX
export CC=clang
export CXX=clang++
bazel build //...

Standard test.sh Template

IMPORTANT: Execution Environment

• $SRC

  is already set (no need for

  : "${SRC:=/src}"

  )
• Working directory is already

  $SRC/{project}

  (no need for

  cd $SRC/{project}

  )

#!/bin/bash
set -ex

# Build (only configure on first run)
if [ ! -f Makefile ]; then
    autoreconf -fi  # or ./bootstrap, or skip if not autotools
    ./configure --options
fi
make -j$(nproc)

# Run tests (use -k to continue on failures, || true to not fail script)
make -k check || true

echo "Tests completed"

Examples by Build System

Autotools Project

#!/bin/bash
set -ex

if [ ! -f Makefile ]; then
    autoreconf -fi
    ./configure --enable-static
fi
make -j$(nproc)
make -k check || true

CMake Project

#!/bin/bash
set -ex

if [ ! -f Makefile ]; then
    cmake . -DCMAKE_INSTALL_PREFIX=$WORK -DBUILD_SHARED_LIBS=off
fi
make -j$(nproc)
make test

Project with Dependencies

#!/bin/bash
set -ex

# Build zlib (only on first run)
if [ ! -f "$WORK/lib/libz.a" ]; then
    pushd "$SRC/zlib"
    ./configure --static --prefix="$WORK"
    make -j$(nproc)
    make install
    popd
fi

# Build main project
if [ ! -f Makefile ]; then
    cmake . -DCMAKE_INSTALL_PREFIX=$WORK
fi
make -j$(nproc)
make test

Project with Submodules (e.g., jq with oniguruma)

#!/bin/bash
set -ex

# Copy submodule if not present (conditional, not delete-and-copy)
if [ ! -d modules/oniguruma ]; then
    mkdir -p modules
    cp -r $SRC/oniguruma modules/
fi

# Remove failing tests from Makefile.am BEFORE configure
sed -i 's| tests/shtest||g' Makefile.am

if [ ! -f Makefile ]; then
    autoreconf -fi
    ./configure --with-oniguruma=builtin
fi
make -j$(nproc)

# Run tests (some may fail in fuzzing environment)
make -k check || true

Common Errors and Fixes

undefined reference to __asan_*

$SRC/test_deps

Makefile:xxx: No rule to make target

if [ ! -f Makefile ]

No rule to make target 'tests/shtest'

source directory already configured

mv: cannot stat: No such file

cp

failed to create tests/*.trs

No rule to make target 'jbig.h'

mv

cp

tiff.dict: No such file

[ -f file ] && cp file dest || true

No rule to make target 'all'

rm -rf && rsync

if [ ! -d dir ]; then cp; fi

%destructor redeclaration

sed -i

if grep -q 'pattern' && ! grep -q 'new_content'

>>

if ! grep -q 'content' file; then ... >> file; fi

ninja: manifest 'build.ninja' still dirty

$SRC

$WORK

ccache: invalid option -- 'U'

export PATH=$(echo "$PATH" | sed 's|/ccache/bin:||g')

Testing Incremental Builds

CRITICAL: Use the

test-inc-build

The subagent runs tests, analyzes logs internally, and returns only essential summary information.

Single Project Test

Task tool:
  subagent_type: "test-inc-build"
  description: "Test incremental build"
  prompt: "Run incremental build test for {project_name} with oss-fuzz path ../oss-fuzz"

AIXCC Projects: Use Full Path Prefix

IMPORTANT: For AIXCC projects, use the

aixcc/c/

aixcc/jvm/

Examples:

• aixcc/c/afc-sqlite3-delta-01

• aixcc/c/atlanta-libjpeg-full-01

• aixcc/jvm/afc-jenkins-delta-01

Parallel Testing Multiple Projects

Use Task tool with

run_in_background: true

Task tool (run_in_background: true):
  subagent_type: "test-inc-build"
  prompt: "Run incremental build test for aixcc/c/afc-libexif-delta-01 with oss-fuzz path ../oss-fuzz"

Task tool (run_in_background: true):
  subagent_type: "test-inc-build"
  prompt: "Run incremental build test for aixcc/c/afc-libexif-delta-02 with oss-fuzz path ../oss-fuzz"

Then use TaskOutput to retrieve results from each agent.

What the Test Does

1. Runs build.sh (first run)
2. Runs docker commit to save state
3. Runs build.sh again (incremental run)
4. Compares build times and reports reduction percentage

Subagent Return Format

On Success:

## Result: SUCCESS
**Project:** {project_name}
**Build Time Reduction:** {percentage}%
**Summary:** Incremental build working correctly.

On Failure:

## Result: FAILED
**Project:** {project_name}
**Error Type:** {category}
**Error Message:** {exact error, max 10 lines}
**Suggested Fix:** {brief fix}

Success criteria:

• Both runs complete without errors
• Build time reduction is reported (higher % = better incremental build support)

Checklist

• Uses

  $SRC

  variable, NOT hardcoded paths like

  /src

  or

  /built-src

• Uses

  if [ ! -f Makefile ]

  guard around configure/autoreconf
• Does NOT delete build artifacts (.o, .lo, .a, .la, .libs)
• Uses

  cp

  instead of

  mv

  where applicable
• Failing tests removed from Makefile.am BEFORE configure (not just file deletion)
• Dependencies have existence guards
• Directory copies are conditional (

  if [ ! -d ]

  ), not delete-and-copy
• Uses

  $SRC

  subdirectories instead of

  $WORK

  for build dirs and install prefixes
• test.sh uses separate prefix (e.g.,

  $SRC/test_deps

  ) if dependencies needed
• Dict/corpus copies use conditional:

  [ -f file ] && cp ... || true

• Tests use

  make -k check || true

  if some may fail
• Internal build.sh rewritten if it uses

  mv

  or non-idempotent operations

• sed -i

  insertions guarded with pattern + content check
• Append operations (

  >>

  ) guarded with content existence check
• CMake/Ninja build directories use

  $SRC

  -relative paths (not

  $WORK

  )
• Bazel builds have ccache removed from PATH
• Works on first run AND repeated runs