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When developing the Dart SDK, various debugging tools and sanitizers can help identify memory errors, race conditions, and undefined behavior.

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Memory Sanitizers

Sanitizers instrument code to detect runtime issues. They require special builds and environment configuration.

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AddressSanitizer (ASan)

Detects memory errors like use-after-free, buffer overflows, and memory leaks.
1

Set environment variables

export ASAN_OPTIONS="handle_segv=0:detect_leaks=1:detect_stack_use_after_return=0:disable_coredump=0:abort_on_error=1"
export ASAN_SYMBOLIZER_PATH="$PWD/buildtools/linux-x64/clang/bin/llvm-symbolizer"
The handle_segv=0 option is crucial when running test suites, as some tests intentionally segfault.
2

Build with ASan

./tools/build.py --mode release --arch x64 --sanitizer asan \
  runtime runtime_precompiled create_sdk
3

Run tests

./tools/sdks/dart-sdk/bin/dart ./tools/test.dart \
  -n dartk-asan-linux-release-x64 \
  -N dartk-asan-linux-release-x64
Legacy approach: 
./tools/gn.py -m release --asan
./tools/build.py -m release runtime
./tools/test.py -m release --builder-tag=asan -t240

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MemorySanitizer (MSan)

Detects reads of uninitialized memory.
1

Set environment variables

export MSAN_OPTIONS="handle_segv=0:detect_leaks=1:detect_stack_use_after_return=0:disable_coredump=0:abort_on_error=1"
export MSAN_SYMBOLIZER_PATH="$PWD/buildtools/linux-x64/clang/bin/llvm-symbolizer"
2

Build with MSan

./tools/build.py --mode release --arch x64 --sanitizer msan \
  runtime runtime_precompiled create_sdk
3

Run tests

./tools/sdks/dart-sdk/bin/dart ./tools/test.dart \
  -n dartk-asan-linux-release-x64 \
  -N dartk-msan-linux-release-x64

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LeakSanitizer (LSan)

Detects memory leaks.
1

Set environment variables

export ASAN_OPTIONS="handle_segv=0:detect_leaks=1:detect_stack_use_after_return=0:disable_coredump=0:abort_on_error=1"
export ASAN_SYMBOLIZER_PATH="$PWD/buildtools/linux-x64/clang/bin/llvm-symbolizer"
2

Build with LSan

./tools/build.py --mode release --arch x64 --sanitizer lsan \
  runtime runtime_precompiled create_sdk
3

Run tests

./tools/sdks/dart-sdk/bin/dart ./tools/test.dart \
  -n dartk-asan-linux-release-x64 \
  -N dartk-lsan-linux-release-x64

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ThreadSanitizer (TSan)

Detects data races and threading issues.
1

Set environment variables

export TSAN_OPTIONS="handle_segv=0:disable_coredump=0:abort_on_error=1"
export TSAN_SYMBOLIZER_PATH="$PWD/buildtools/linux-x64/clang/bin/llvm-symbolizer"
2

Build with TSan

./tools/build.py --mode release --arch x64 --sanitizer tsan \
  dart runtime runtime_precompiled create_sdk
3

Run tests

./tools/sdks/dart-sdk/bin/dart ./tools/test.dart \
  -n dartk-asan-linux-release-x64 \
  -N dartk-tsan-linux-release-x64
Legacy approach: 
./tools/gn.py -m release --tsan
./tools/build.py -m release runtime
./tools/test.py -m release

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UndefinedBehaviorSanitizer (UBSan)

Detects undefined behavior like integer overflow, null pointer dereference, etc.
1

Set environment variables

export UBSAN_OPTIONS="handle_segv=0:disable_coredump=0:abort_on_error=1"
export UBSAN_SYMBOLIZER_PATH="$PWD/buildtools/linux-x64/clang/bin/llvm-symbolizer"
2

Build with UBSan

./tools/build.py --mode release --arch x64 --sanitizer ubsan \
  runtime runtime_precompiled create_sdk
3

Run tests

./tools/sdks/dart-sdk/bin/dart ./tools/test.dart \
  -n dartk-linux-release-x64 \
  -N dartk-ubsan-linux-release-x64

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Debugging VM Code

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Noopt Mode

Disables JIT optimization for easier debugging: 
# Build noopt runtime
./tools/build.py -mdebug,release runtime_and_noopt

# Run tests without optimization
./tools/test.py -mdebug,release --noopt

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ASan with VM Development

AddressSanitizer works at the C++ level and doesn’t automatically know about JIT-generated code or low-level stack manipulation.

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Manual Stack Unpoisoning

Use the ASAN_UNPOISON(ptr, len) macro to inform ASan about stack regions manipulated outside normal C++ code: 
// After manually manipulating stack
ASAN_UNPOISON(stack_ptr, stack_size);

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Getting Real Stack Pointer

When running with detect_stack_use_after_return=1, ASan returns fake stack pointers. Use Isolate::GetCurrentStackPointer() to get the real stack pointer: 
uword stack_ptr = Isolate::GetCurrentStackPointer();
This calls a pregenerated stub to bypass ASan’s instrumentation.

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Testing Precompilation

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Standard Precompilation

./tools/build.py -mrelease runtime_precompiled
./tools/test.py -mrelease -cprecompiler -rdart_precompiled

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Precompilation on Android

1

Build for Android

./tools/build.py -mrelease -aarm --os=android runtime_precompiled
2

Add ADB to PATH

export PATH=$PATH:$PWD/third_party/android_tools/sdk/platform-tools
3

Run tests on device

./tools/test.py -mrelease -aarm --system=android \
  -cprecompiler -rdart_precompiled --use-blobs

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Quick Minimal Tests

For rapid iteration during development, use these minimal test commands:

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macOS

./tools/build.py -mrelease dart2js
./sdk/bin/dart2js_developer -v --categories=all \
  --package-root=out/ReleaseIA32/packages/ \
  tests/utils/dummy_compiler_test.dart

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Linux

./tools/build.py -mrelease dart2js
./sdk/bin/dart2js_developer -v --categories=all \
  --package-root=out/ReleaseIA32/packages/ \
  tests/utils/dummy_compiler_test.dart

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Windows

python ./tools/build.py -mrelease dart2js
sdk\bin\dart2js_developer.bat -v --categories=all \
  --package-root=out/ReleaseIA32/packages/ \
  tests/utils/dummy_compiler_test.dart
Minimal tests are quick but may miss issues. Always run full test suites before submitting.

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