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+=====================================
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+Cross Translation Unit (CTU) Analysis
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+=====================================
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+
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+Normally, static analysis works in the boundary of one translation unit (TU).
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+However, with additional steps and configuration we can enable the analysis to inline the definition of a function from another TU.
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+
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+.. contents::
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+ :local:
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+
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+Manual CTU Analysis
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+-------------------
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+
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+Let's consider these source files in our minimal example:
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+
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+.. code-block:: cpp
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+
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+ // main.cpp
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+ int foo();
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+
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+ int main() {
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+ return 3 / foo();
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+ }
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+
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+.. code-block:: cpp
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+
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+ // foo.cpp
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+ int foo() {
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+ return 0;
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+ }
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+
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+And a compilation database:
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+
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+.. code-block:: bash
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+
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+ [
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+ {
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+ "directory": "/path/to/your/project",
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+ "command": "clang++ -c foo.cpp -o foo.o",
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+ "file": "foo.cpp"
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+ },
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+ {
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+ "directory": "/path/to/your/project",
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+ "command": "clang++ -c main.cpp -o main.o",
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+ "file": "main.cpp"
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+ }
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+ ]
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+
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+We'd like to analyze `main.cpp` and discover the division by zero bug.
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+In order to be able to inline the definition of `foo` from `foo.cpp` first we have to generate the `AST` (or `PCH`) file of `foo.cpp`:
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+
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+.. code-block:: bash
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+
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+ $ pwd $ /path/to/your/project
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+ $ clang++ -emit-ast -o foo.cpp.ast foo.cpp
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+ $ # Check that the .ast file is generated:
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+ $ ls
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+ compile_commands.json foo.cpp.ast foo.cpp main.cpp
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+ $
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+
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+The next step is to create a CTU index file which holds the `USR` name and location of external definitions in the source files:
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+
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+.. code-block:: bash
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+
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+ $ clang-extdef-mapping -p . foo.cpp
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+ c:@F@foo# /path/to/your/project/foo.cpp
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+ $ clang-extdef-mapping -p . foo.cpp > externalDefMap.txt
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+
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+We have to modify `externalDefMap.txt` to contain the name of the `.ast` files instead of the source files:
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+
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+.. code-block:: bash
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+
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+ $ sed -i -e "s/.cpp/.cpp.ast/g" externalDefMap.txt
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+
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+We still have to further modify the `externalDefMap.txt` file to contain relative paths:
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+
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+.. code-block:: bash
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+
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+ $ sed -i -e "s|$(pwd)/||g" externalDefMap.txt
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+
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+Now everything is available for the CTU analysis.
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+We have to feed Clang with CTU specific extra arguments:
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+
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+.. code-block:: bash
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+
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+ $ pwd
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+ /path/to/your/project
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+ $ clang++ --analyze -Xclang -analyzer-config -Xclang experimental-enable-naive-ctu-analysis=true -Xclang -analyzer-config -Xclang ctu-dir=. -Xclang -analyzer-output=plist-multi-file main.cpp
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+ main.cpp:5:12: warning: Division by zero
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+ return 3 / foo();
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+ ~~^~~~~~~
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+ 1 warning generated.
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+ $ # The plist file with the result is generated.
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+ $ ls
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+ compile_commands.json externalDefMap.txt foo.ast foo.cpp foo.cpp.ast main.cpp main.plist
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+ $
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+
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+This manual procedure is error-prone and not scalable, therefore to analyze real projects it is recommended to use `CodeChecker` or `scan-build-py`.
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+
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+Automated CTU Analysis with CodeChecker
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+---------------------------------------
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+The `CodeChecker <https://github.com/Ericsson/codechecker>`_ project fully supports automated CTU analysis with Clang.
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+Once we have set up the `PATH` environment variable and we activated the python `venv` then it is all it takes:
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+
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+.. code-block:: bash
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+
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+ $ CodeChecker analyze --ctu compile_commands.json -o reports
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+ [INFO 2019-07-16 17:21] - Pre-analysis started.
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+ [INFO 2019-07-16 17:21] - Collecting data for ctu analysis.
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+ [INFO 2019-07-16 17:21] - [1/2] foo.cpp
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+ [INFO 2019-07-16 17:21] - [2/2] main.cpp
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+ [INFO 2019-07-16 17:21] - Pre-analysis finished.
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+ [INFO 2019-07-16 17:21] - Starting static analysis ...
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+ [INFO 2019-07-16 17:21] - [1/2] clangsa analyzed foo.cpp successfully.
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+ [INFO 2019-07-16 17:21] - [2/2] clangsa analyzed main.cpp successfully.
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+ [INFO 2019-07-16 17:21] - ----==== Summary ====----
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+ [INFO 2019-07-16 17:21] - Successfully analyzed
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+ [INFO 2019-07-16 17:21] - clangsa: 2
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+ [INFO 2019-07-16 17:21] - Total analyzed compilation commands: 2
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+ [INFO 2019-07-16 17:21] - ----=================----
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+ [INFO 2019-07-16 17:21] - Analysis finished.
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+ [INFO 2019-07-16 17:21] - To view results in the terminal use the "CodeChecker parse" command.
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+ [INFO 2019-07-16 17:21] - To store results use the "CodeChecker store" command.
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+ [INFO 2019-07-16 17:21] - See --help and the user guide for further options about parsing and storing the reports.
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+ [INFO 2019-07-16 17:21] - ----=================----
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+ [INFO 2019-07-16 17:21] - Analysis length: 0.659618854523 sec.
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+ $ ls
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+ compile_commands.json foo.cpp foo.cpp.ast main.cpp reports
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+ $ tree reports
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+ reports
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+ ├── compile_cmd.json
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+ ├── compiler_info.json
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+ ├── foo.cpp_53f6fbf7ab7ec9931301524b551959e2.plist
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+ ├── main.cpp_23db3d8df52ff0812e6e5a03071c8337.plist
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+ ├── metadata.json
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+ └── unique_compile_commands.json
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+
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+ 0 directories, 6 files
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+ $
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+
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+The `plist` files contain the results of the analysis, which may be viewed with the regular analysis tools.
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+E.g. one may use `CodeChecker parse` to view the results in command line:
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+
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+.. code-block:: bash
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+
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+ $ CodeChecker parse reports
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+ [HIGH] /home/egbomrt/ctu_mini_raw_project/main.cpp:5:12: Division by zero [core.DivideZero]
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+ return 3 / foo();
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+ ^
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+
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+ Found 1 defect(s) in main.cpp
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+
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+
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+ ----==== Summary ====----
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+ -----------------------
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+ Filename | Report count
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+ -----------------------
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+ main.cpp | 1
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+ -----------------------
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+ -----------------------
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+ Severity | Report count
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+ -----------------------
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+ HIGH | 1
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+ -----------------------
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+ ----=================----
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+ Total number of reports: 1
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+ ----=================----
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+
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+Or we can use `CodeChecker parse -e html` to export the results into HTML format:
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+
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+.. code-block:: bash
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+
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+ $ CodeChecker parse -e html -o html_out reports
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+ $ firefox html_out/index.html
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+
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+If you experience that Clang crashes during the visitation of the BugPath then please disable macro expansion when CTU is used:
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+
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+.. code-block:: bash
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+
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+ $ echo "-Xclang -analyzer-stats -Xclang -analyzer-config -Xclang expand-macros=false" >./saargs_file
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+ $ CodeChecker analyze --ctu --saargs ./saargs_file compile_commands.json -o reports
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+
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+We have a patch which will solve this issue soon.
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+
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+Automated CTU Analysis with scan-build-py (don't do it)
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+-------------------------------------------------------
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+We actively develop CTU with CodeChecker as a "runner" script, `scan-build-py` is not actively developed for CTU.
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+`scan-build-py` has various errors and issues, expect it to work with the very basic projects only.
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+
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+Example usage of scan-build-py:
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+
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+.. code-block:: bash
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+
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+ $ /your/path/to/llvm-project/clang/tools/scan-build-py/bin/analyze-build --ctu
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+ analyze-build: Run 'scan-view /tmp/scan-build-2019-07-17-17-53-33-810365-7fqgWk' to examine bug reports.
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+ $ /your/path/to/llvm-project/clang/tools/scan-view/bin/scan-view /tmp/scan-build-2019-07-17-17-53-33-810365-7fqgWk
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+ Starting scan-view at: http://127.0.0.1:8181
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+ Use Ctrl-C to exit.
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+ [6336:6431:0717/175357.633914:ERROR:browser_process_sub_thread.cc(209)] Waited 5 ms for network service
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+ Opening in existing browser session.
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+ ^C
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+ $
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