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source_debugging_interpreter.md

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WAMR source debugging (interpreter)

References:

WAMR supports source level debugging based on DWARF (normally used in C/C++/Rust), source map (normally used in AssemblyScript) is not supported.

The lldb's ability to debug wasm application is based on the patch Add class WasmProcess for WebAssembly debugging. Thanks very much to the author @paolosev for such a great work!

Debugging with interpreter

  1. Install dependent libraries
apt update && apt install cmake make g++ libxml2-dev -y
  1. Build iwasm with source debugging feature
cd ${WAMR_ROOT}/product-mini/platforms/linux
mkdir build && cd build
cmake .. -DWAMR_BUILD_DEBUG_INTERP=1
make

Note: On MacOS M1 environment, pass the additional -DWAMR_DISABLE_HW_BOUND_CHECK=1 cmake configuration.

  1. Execute iwasm with debug engine enabled
iwasm -g=127.0.0.1:1234 test.wasm
# Use port = 0 to allow a random assigned debug port
  1. Build customized lldb
git clone --branch release/13.x --depth=1 https://github.com/llvm/llvm-project
cd llvm-project
git apply ${WAMR_ROOT}/build-scripts/lldb_wasm.patch
mkdir build-lldb
cmake -S ./llvm -B build-lldb \
    -G Ninja \
    -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang;lldb" \
    -DLLVM_TARGETS_TO_BUILD:STRING="X86;WebAssembly" \
    -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DLLVM_BUILD_BENCHMARKS:BOOL=OFF \
    -DLLVM_BUILD_DOCS:BOOL=OFF  -DLLVM_BUILD_EXAMPLES:BOOL=OFF  \
    -DLLVM_BUILD_LLVM_DYLIB:BOOL=OFF  -DLLVM_BUILD_TESTS:BOOL=OFF  \
    -DLLVM_ENABLE_BINDINGS:BOOL=OFF  -DLLVM_INCLUDE_BENCHMARKS:BOOL=OFF  \
    -DLLVM_INCLUDE_DOCS:BOOL=OFF  -DLLVM_INCLUDE_EXAMPLES:BOOL=OFF  \
    -DLLVM_INCLUDE_TESTS:BOOL=OFF -DLLVM_ENABLE_LIBXML2:BOOL=ON
cmake --build build-lldb --target lldb --parallel $(nproc)
# The lldb is generated under build-lldb/bin/lldb

Note: If using CommandLineTools on MacOS, make sure only one SDK is present in /Library/Developer/CommandLineTools/SDKs.

You can download pre-built wamr-lldb binaries from here.

  1. Launch customized lldb and connect to iwasm
lldb
(lldb) process connect -p wasm connect://127.0.0.1:1234

Then you can use lldb commands to debug your applications. Please refer to lldb document for command usage.

Enable debugging in embedders (for interpreter)

There are three steps to enable debugging in embedders

  1. Set the debug parameters when initializing the runtime environment:

    RuntimeInitArgs init_args;
memset(&init_args, 0, sizeof(RuntimeInitArgs));

/* ... */
strcpy(init_args.ip_addr, "127.0.0.1");
init_args.instance_port = 1234;
/*
* Or set port to 0 to use a port assigned by os
* init_args.instance_port = 0;
*/

if (!wasm_runtime_full_init(&init_args)) {
    return false;
}

  2. Use wasm_runtime_start_debug_instance to create the debug instance:

    /*
    initialization, loading and instantiating
    ...
*/
exec_env = wasm_runtime_create_exec_env(module_inst, stack_size);
uint32_t debug_port = wasm_runtime_start_debug_instance(exec_env);

  3. Enable source debugging features during building

    You can use -DWAMR_BUILD_DEBUG_INTERP=1 during cmake configuration

    Or you can set it directly in cmake files:

    set (WAMR_BUILD_DEBUG_INTERP 1)

Attentions

  • Debugging multi-thread wasm module is not supported, if your wasm module use pthread APIs (see pthread_library.md), or the embedder use wasm_runtime_spawn_thread to create new wasm threads, then there may be unexpected behaviour during debugging.

    Note: This attention is about "wasm thread" rather than native threads. Executing wasm functions in several different native threads will not affect the normal behaviour of debugging feature.

  • When using source debugging features, don't create multiple wasm_instance from the same wasm_module, because the debugger may change the bytecode (set/unset breakpoints) of the wasm_module. If you do need several instance from the same bytecode, you need to copy the bytecode to a new butter, then load a new wasm_module, and then instantiate the new wasm module to get the new instance.

  • If you are running lldb on non-linux platforms, please use platform select remote-linux command in lldb before connecting to the runtime:

    (lldb) platform select remote-linux
(lldb) process connect -p wasm connect://127.0.0.1:1234