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WAMR Source Debugging With LLDB

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!

Build wasm application with debug information

To debug your application, you need to compile them with debug information. You can use -g option when compiling the source code if you are using wasi-sdk (also work for emcc and rustc):
/opt/wasi-sdk/bin/clang -g test.c -o test.wasm
Then you will get test.wasm which is a WebAssembly module with embedded DWARF sections. Further, you can use llvm-dwarfdump to check if the generated wasm file contains DWARF information:
llvm-dwarfdump-12 test.wasm

Debugging with interpreter

  1. 1.
    Install dependent libraries
apt update && apt install cmake make g++ libxml2-dev -y
  1. 2.
    Build iwasm with source debugging feature
cd ${WAMR_ROOT}/product-mini/platforms/linux
mkdir build && cd build
Note: On MacOS M1 environment, pass the additional -DWAMR_DISABLE_HW_BOUND_CHECK=1 cmake configuration.
  1. 3.
    Execute iwasm with debug engine enabled
iwasm -g= test.wasm
# Use port = 0 to allow a random assigned debug port
  1. 4.
    Build customized lldb
git clone --branch release/13.x --depth=1
cd llvm-project
git apply ${WAMR_ROOT}/build-scripts/lldb_wasm.patch
mkdir build-lldb
cmake -S ./llvm -B build-lldb \
-G Ninja \
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. 5.
    Launch customized lldb and connect to iwasm
(lldb) process connect -p wasm connect://
Then you can use lldb commands to debug your applications. Please refer to lldb document for command usage.

Debugging with AOT

Note: AOT debugging is experimental and only a few debugging capabilities are supported.
  1. 1.
    Build lldb (assume you have already built llvm)
cd ${WAMR_ROOT}/core/deps/llvm/build
make -j $(nproc)
  1. 2.
    Build wamrc with debugging feature
cd ${WAMR_ROOT}/wamr-compiler
mkdir build && cd build
make -j $(nproc)
  1. 3.
    Build iwasm with debugging feature
cd ${WAMR_ROOT}/product-mini/platforms/linux
mkdir build && cd build
  1. 4.
    Compile wasm module to AOT module
wamrc -o test.aot test.wasm
  1. 5.
    Execute iwasm using lldb
    Then you can use lldb commands to debug both wamr runtime and your wasm application in current terminal.
    % lldb iwasm -- test.aot
    (lldb) target create "iwasm"
    Current executable set to 'iwasm' (x86_64).
    (lldb) settings set -- "test.aot"
    (lldb) settings set plugin.jit-loader.gdb.enable on
    (lldb) b main
    Breakpoint 1: where = iwasm`main + 48 at main.c:294:11, address = 0x0000000100001020
    (lldb) run
    Process 27954 launched: '/tmp/bin/iwasm' (x86_64)
    Process 27954 stopped
    * thread #1, queue = '', stop reason = breakpoint 1.1
    frame #0: 0x0000000100001020 iwasm`main(argc=2, argv=0x00007ff7bfeff678) at main.c:294:11
    291 int
    292 main(int argc, char *argv[])
    293 {
    -> 294 int32 ret = -1;
    295 char *wasm_file = NULL;
    296 const char *func_name = NULL;
    297 uint8 *wasm_file_buf = NULL;
    Target 0: (iwasm) stopped.
    (lldb) c
    Process 27954 resuming
    1 location added to breakpoint 1
    error: need to add support for DW_TAG_base_type 'void' encoded with DW_ATE = 0x0, bit_size = 0
    Process 27954 stopped
    * thread #1, queue = '', stop reason = breakpoint 1.2
    frame #0: 0x00000001002980a0 JIT(0x100298004)`main(exenv=0x0000000301808200) at hello.c:6:9
    3 int
    4 main(void)
    5 {
    -> 6 printf("hello\n");
    8 return 0;
    9 }
    Target 0: (iwasm) stopped.
    (lldb) br l
    Current breakpoints:
    1: name = 'main', locations = 2, resolved = 2, hit count = 2
    1.1: where = iwasm`main + 48 at main.c:294:11, address = 0x0000000100001020, resolved, hit count = 1
    1.2: where = JIT(0x100298004)`main + 12 at hello.c:6:9, address = 0x00000001002980a0, resolved, hit count = 1
    • In the above example,
      • The first main function, which is in main.c, is the main function of the iwasm command.
      • The second main function, which is in hello.c, is the main function of the AOT-compiled wasm module.
    • WAMR AOT debugging uses the GDB JIT loader mechanism to load the debug info of the debugee module. On some platforms including macOS, you need to enable it explicitly. (settings set plugin.jit-loader.gdb.enable on)

Enable debugging in embedders (for interpreter)

There are three steps to enable debugging in embedders
  1. 1.
    Set the debug parameters when initializing the runtime environment:
    RuntimeInitArgs init_args;
    memset(&init_args, 0, sizeof(RuntimeInitArgs));
    /* ... */
    strcpy(init_args.ip_addr, "");
    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. 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. 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:


  • Debugging multi-thread wasm module is not supported, if your wasm module use pthread APIs (see, 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://