pw_assert_tokenized#

Overview#

The pw_assert_tokenized module provides PW_ASSERT() and PW_CHECK_*() backends for the pw_assert module. These backends are much more space efficient than using pw_assert_log with pw_log_tokenized The tradeoff, however, is that PW_CHECK_*() macros are much more limited as all argument values are discarded. This means only constant string information is captured in the reported tokens.

  • PW_ASSERT(): The PW_ASSERT() macro will capture the file name and line number of the assert statement. By default, it is passed to the logging system to produce a string like this:

    PW_ASSERT() or PW_DASSERT() failure at pw_result/public/pw_result/result.h:63

  • PW_CHECK_*(): The PW_CHECK_*() macros work in contexts where tokenization is fully supported, so they are able to capture the CHECK statement expression and any provided string literal in addition to the file name in the pw_log_tokenized key/value format:

    “■msg♦Check failure: *unoptimizable >= 0, Ensure this CHECK logic stays■module♦KVS■file♦pw_kvs/size_report/base.cc”

    Evaluated values of PW_CHECK_*() statements are not captured, and any string formatting arguments are also not captured. This minimizes call-site cost as only two arguments are ever passed to the handler (the calculated token, and the line number of the statement).

    Note that the line number is passed to the tokenized logging system as metadata, but is not part of the tokenized string. This is to ensure the CHECK callsite maximizes efficiency by only passing two arguments to the handler.

In both cases, the assert handler is only called with two arguments: a 32-bit token to represent a string, and the integer line number of the callsite.

Setup#

  1. Set pw_assert_BACKEND = "$dir_pw_assert_tokenized:check_backend" and pw_assert_LITE_BACKEND = "$dir_pw_assert_tokenized:assert_backend" in your target configuration.

  2. Ensure your target provides pw_tokenizer_GLOBAL_HANDLER_BACKEND. By default, pw_assert_tokenized will forward assert failures to the tokenizer handler as logs. The tokenizer handler should check for LOG_LEVEL_FATAL and properly divert to a crash handler.

  3. Add file name tokens to your token database. pw_assert_tokenized can’t create file name tokens that can be parsed out of the final compiled binary. The pw_relative_source_file_names GN template can be used to collect the names of all source files used in your final executable into a JSON file, which can then be included in the creation of a tokenizer database.

Example file name token database setup#

pw_executable("main") {
  deps = [
    # ...
  ]
  sources = [ "main.cc" ]
}

pw_tokenizer_database("log_tokens") {
  database = "tools/tokenized_logs.csv"
  deps = [
    ":source_file_names",
    ":main",
  ]
  optional_paths = [ "$root_build_dir/**/*.elf" ]
  input_databases = [ "$target_gen_dir/source_file_names.json" ]
}

# Extracts all source/header file names from "main" and its transitive
# dependencies for tokenization.
pw_relative_source_file_names("source_file_names") {
  deps = [ ":main" ]
  outputs = [ "$target_gen_dir/source_file_names.json" ]
}

Warning

This module is experimental and does not provide a stable API.