Trace Annotator Tool

Introduction

A tool to annotate functions with c++ TRACE_EVENT. This tool serves two workflows:

• Debugging: bulk add traces to all functions in a directory and after finding the bug remove the traces.
• Adding traces to code: bulk add traces to all functions in a directory, review the changes carefully and create a patch.

The goal of this tool is to transfer a function:

int foo(int bar, int baz) {
  return 42;
}

into:

int foo(int bar, int baz) {
  TRACE_EVENT0("test", "foo");
  return 42;
}

In future also argument tracing is to be supported.

This document is based on //docs/clang_tool_refactoring.md

Building

The following might take approx. 2 hours depending on your computer.

• Make a new checkout of chromium (suggested, but optional).
• From chromium/src:
• shell cr build all To make sure all files have been generated.
• shell cp -R third_party/llvm-build ~

• --without-fuchsia --extra-tools trace_annotator```
  *  TODO how to build with plugin 'find-bad-constructs'?
  

• shell cp -R ~/llvm-build third_party This should enable goma support again.

Rebuild just the tool:

• shell cd third_party/llvm-build/Release+Asserts
• shell ninja trace_annotator

Beware that running shell gclient sync might overwrite the build and another full build might be necessary. A backup of the binary from //third_party/llvm-build/Release+Asserts/bin/trace_annotator might be useful.

Testing

• shell tools/clang/scripts/test_tool.py --apply-edits trace_annotator

Running

• Chrome plugins are not supported yet, run: shell gn args out/Debug/ and add: clang_use_chrome_plugins = false option.

• Make sure you have up to date compilation database:

  • To generate it run: shell tools/clang/scripts/generate_compdb.py -p out/Debug/ > out/Debug/compile_commands.json
  • These are the compiler options for individual files (needed to use the right version of C++, right library paths...).

•    git checkout $DIR && tools/clang/scripts/run_tool.py --tool trace_annotator -p out/Debug/ $DIR \
     | tools/clang/scripts/extract_edits.py \
     | tools/clang/scripts/apply_edits.py -p out/Debug $DIR \
     && git cl format $DIR```
  
  

• Consult documentation of //tools/clang/scripts/run_tool.py for more options.

Suggestion:

Do not run the tool on //base or anything that has to do with tracing or synchronization. Or at least do not submit the resulting patch.

Debugging workflow suggestion:

• Do some changes.
• shell git add . ; git commit
• Run the tool.
• shell git add . ; git commit
• Do some more changes (including fixing a bug).
• shell git add . ; git commit
• shell git rebase -i and follow the help.

Creating tracing patch suggestion:

• Run the tool.
• Double check all generated code.
• Add method annotations for methods that are hidden by compiler options (e.g., if you are on unix then the code in c++ #ifdef OS_WIN will not be annotated.

TODO

• Add options:
  • Whether to add “do not submit” comment (in upper case).
  • Function name formatting (without namespace(s) / getQualifiedNameAsString / with namespaces but without template tags).
  • Category name.
  • Make tracing of function arguments.
• Standalone build of the tool (outside of //third_party to avoid overwriting by shell gclient sync).