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134 lines
4.5 KiB
Markdown
134 lines
4.5 KiB
Markdown
# "debug-tools" sample introduction
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Tool to symoblicate stack traces. When using wasm in production, debug info are usually stripped using tools like `wasm-opt`, to decrease the binary size. If a corresponding unstripped wasm file is kept, location information (function, file, line, column) can be retrieved from the stripped stack trace.
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## Build and run the sample
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### Generate the stack trace
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Build `iwasm` with `WAMR_BUILD_DUMP_CALL_STACK=1` and `WAMR_BUILD_FAST_INTERP=0` and the wasm file with debug info (e.g. `clang -g`). As it is done in [CMakeLists.txt](./CMakeLists.txt) and [wasm-apps/CMakeLists.txt](./wasm-apps/CMakeLists.txt) (look for `addr2line`):
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```bash
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$ mkdir build && cd build
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$ cmake ..
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$ make
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$ ./iwasm wasm-apps/trap.wasm
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```
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The output should be something like
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```text
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#00: 0x0159 - $f5
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#01: 0x01b2 - $f6
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#02: 0x0200 - $f7
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#03: 0x026b - $f8
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#04: 0x236b - $f15
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#05: 0x011f - _start
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Exception: unreachable
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```
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Copy the stack trace printed to stdout into a separate file (`call_stack.txt`):
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```bash
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$ ./iwasm wasm-apps/trap.wasm | grep "#" > call_stack.txt
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```
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Same for AOT. The AOT binary has to be generated using the `--enable-dump-call-stack` option of `wamrc`, as in [CMakeLists.txt](./wasm-apps/CMakeLists.txt). Then run:
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```bash
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$ ./iwasm wasm-apps/trap.aot | grep "#" > call_stack.txt
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```
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### Symbolicate the stack trace
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Run the [addr2line](../../test-tools/addr2line/addr2line.py) script to symbolicate the stack trace:
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```bash
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$ python3 ../../../test-tools/addr2line/addr2line.py \
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--wasi-sdk /opt/wasi-sdk \
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--wabt /opt/wabt \
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--wasm-file wasm-apps/trap.wasm \
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call_stack.txt
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```
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The output should be something like:
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```text
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0: c
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at wasm-micro-runtime/samples/debug-tools/wasm-apps/trap.c:5:1
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1: b
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at wasm-micro-runtime/samples/debug-tools/wasm-apps/trap.c:11:12
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2: a
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at wasm-micro-runtime/samples/debug-tools/wasm-apps/trap.c:17:12
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3: main
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at wasm-micro-runtime/samples/debug-tools/wasm-apps/trap.c:24:5
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4: __main_void
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at unknown:?:?
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5: _start
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```
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If WAMR is run in fast interpreter mode (`WAMR_BUILD_FAST_INTERP=1`), addresses in the stack trace cannot be tracked back to location info.
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If WAMR <= `1.3.2` is used, the stack trace does not contain addresses.
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In those two cases, run the script with `--no-addr`: the line info returned refers to the start of the function
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```bash
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$ python3 ../../../test-tools/addr2line/addr2line.py \
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--wasi-sdk /opt/wasi-sdk \
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--wabt /opt/wabt \
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--wasm-file wasm-apps/trap.wasm \
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call_stack.txt --no-addr
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```
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#### sourcemap
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This script also supports _sourcemap_ which is produced by [_emscripten_](https://emscripten.org/docs/tools_reference/emcc.html). The _sourcemap_ is used to map the wasm function to the original source file. To use it, add `-gsource-map` option to _emcc_ command line. The output should be a section named "sourceMappingURL" and a separated file named "_.map_.
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If the wasm file is with _sourcemap_, the script will use it to get the source file and line info. It needs an extra command line option `--emsdk` to specify the path of _emsdk_. The script will use _emsymbolizer_ to query the source file and line info.
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````bash
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$ python3 ../../../test-tools/addr2line/addr2line.py \
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--wasi-sdk /opt/wasi-sdk \
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--wabt /opt/wabt \
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--wasm-file emscripten/wasm-apps/trap.wasm \
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--emsdk /opt/emsdk \
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call_stack.from_wasm_w_sourcemap.txt
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The output should be something like:
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```text
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1: c
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at ../../../../../wasm-apps/trap.c:5:1
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2: b
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at ../../../../../wasm-apps/trap.c:11:12
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3: a
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at ../../../../../wasm-apps/trap.c:17:12
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4: main
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at ../../../../../wasm-apps/trap.c:24:5
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5: __main_void
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at ../../../../../../../../../emsdk/emscripten/system/lib/standalone/__main_void.c:53:10
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6: _start
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at ../../../../../../../../../emsdk/emscripten/system/lib/libc/crt1.c:27:3
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````
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> The script assume the separated map file _.map_ is in the same directory as the wasm file.
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### Another approach
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If the wasm file is with "name" section, it is able to output function name in the stack trace. To achieve that, need to enable `WAMR_BUILD_LOAD_CUSTOM_SECTION` and `WAMR_BUILD_CUSTOM_NAME_SECTION`. If using .aot file, need to add `--emit-custom-sections=name` into wamrc command line options.
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Then the output should be something like
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```text
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#00: 0x0159 - c
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#01: 0x01b2 - b
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#02: 0x0200 - a
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#03: 0x026b - main
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#04: 0x236b - __main_void
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#05: 0x011f - _start
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Exception: unreachable
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```
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Also, it is able to use _addr2line.py_ to add file and line info to the stack trace.
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