c-static-analysis

Testing & Quality

Run Clang static analysis on Julia's C/C++ runtime and codegen, and satisfy the GC-rooting checker. Use after modifying runtime/codegen .c/.cpp files under src/ (excluding headers), before opening a PR.

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C/C++ static analysis (src/)

Use this after you modify a runtime/codegen C/C++ source file under src/ (not headers). Note that runtime changes also require a rebuild (make -j).

Run static analysis checks:

First run make -C src install-analysis-deps to initialize dependencies (only needed once the first time, or after the LLVM/Clang toolchain dependencies change). This may download and install LLVM/Clang artifacts.
For a source file such as src/jloptions.c or src/codegen.cpp, use the file stem without the .c/.cpp extension:
```
make -C src analyze-<file-stem> -j8 [--output-sync]
```
For example, to analyze src/jloptions.c, run:
```
make -C src analyze-jloptions -j8
```
Add --output-sync when your make supports it to keep parallel output grouped; otherwise omit it.
Checks can also be rerun individually with clang-sa-<file-stem>, clang-sagc-<file-stem> or clang-tidy-<file-stem>.

Fixing the GC-rooting checker (clang-sagc)

If clang-sagc-<file-stem> fails, first look for fixes that establish real rooting, such as adding appropriate JL_GC_PUSH/JL_GC_POP scopes, or for lock/control-flow fixes.

Do not add JL_GC_PROMISE_ROOTED without explicit user or maintainer confirmation. JL_GC_PROMISE_ROOTED asserts that a value is already rooted; it does not root the value. If it appears necessary, stop and ask for confirmation, showing the exact expression, the existing root that makes it safe, and the safepoints considered.

Remember arguments are assumed rooted, so check the callers to make sure that is handled.
As a diagnostic hint when asking for confirmation: if the value is temporarily moved through a struct or arraylist and then reloaded, the promised expression may need to refer to the reloaded field, such as JL_GC_PROMISE_ROOTED(struct->field), immediately after the reload and before any use of that field.
If confirmed, put the promise as early in the code as is legal, near the definition or reload rather than the use.