[clang] [rtsan][NFC] Documentation of suppression flag (PR #112727)
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Thu Oct 17 08:23:17 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Chris Apple (cjappl)
<details>
<summary>Changes</summary>
---
Full diff: https://github.com/llvm/llvm-project/pull/112727.diff
1 Files Affected:
- (modified) clang/docs/RealtimeSanitizer.rst (+62-4)
``````````diff
diff --git a/clang/docs/RealtimeSanitizer.rst b/clang/docs/RealtimeSanitizer.rst
index 103842e055db70..bec15fd6cad2ac 100644
--- a/clang/docs/RealtimeSanitizer.rst
+++ b/clang/docs/RealtimeSanitizer.rst
@@ -183,6 +183,10 @@ A **partial** list of flags RealtimeSanitizer respects:
- ``true``
- boolean
- If set, use the symbolizer to turn virtual addresses to file/line locations. If false, can greatly speed up the error reporting.
+ * - ``suppressions``
+ - ""
+ - path
+ - If set to a valid suppressions file, will suppress issue reporting. See details in "Disabling", below.
Some issues with flags can be debugged using the ``verbosity=$NUM`` flag:
@@ -194,12 +198,43 @@ Some issues with flags can be debugged using the ``verbosity=$NUM`` flag:
misspelled_flag
...
-Disabling
----------
+Disabling and suppressing
+-------------------------
-In some circumstances, you may want to suppress error reporting in a specific scope.
+There are multiple ways to suppress error reporting when using RealtimeSanitizer.
-In C++, this is achieved via ``__rtsan::ScopedDisabler``. Within the scope where the ``ScopedDisabler`` object is instantiated, all sanitizer error reports are suppressed. This suppression applies to the current scope as well as all invoked functions, including any functions called transitively.
+In general, ``ScopedDisabler`` should be preferred, as it is the most performant.
+
+.. list-table:: Suppression methods
+ :widths: 30 15 15 10 70
+ :header-rows: 1
+
+ * - Suppression method
+ - Specified at?
+ - Scope
+ - Run-time cost
+ - Description
+ * - ``ScopedDisabler``
+ - Compile-time
+ - Stack
+ - Very low
+ - Suppresses all sanitizer error reports in the current scope and all invoked functions.
+ * - ``function-name-matches`` suppression
+ - Run-time
+ - Single function
+ - Medium
+ - Suppresses intercepted and ``[[clang::blocking]]`` function calls by name.
+ * - ``call-stack-contains`` suppression
+ - Run-time
+ - Stack
+ - High
+ - Suppresses any stack trace contaning the specified pattern.
+
+
+``ScopedDisabler``
+##################
+
+At compile time, RealtimeSanitizer may be disabled for a scope using ``__rtsan::ScopedDisabler``. Within the scope where the ``ScopedDisabler`` object is instantiated, all sanitizer error reports are suppressed. This suppression applies to the current scope as well as all invoked functions, including any functions called transitively.
.. code-block:: c++
@@ -233,6 +268,29 @@ In C, you can use the ``__rtsan_disable()`` and ``rtsan_enable()`` functions to
Each call to ``__rtsan_disable()`` must be paired with a subsequent call to ``__rtsan_enable()`` to restore normal sanitizer functionality. If a corresponding ``rtsan_enable()`` call is not made, the behavior is undefined.
+Suppression file
+################
+
+At run-time, suppressions may be specified using a suppressions file passed in ``RTSAN_OPTIONS``. Run-time suppression may be useful if the source cannot be changed.
+
+.. code-block:: console
+
+ > cat suppressions.supp
+ call-stack-contains:MallocViolation
+ call-stack-contains:std::*vector
+ function-name-matches:free
+ function-name-matches:CustomMarkedBlocking*
+ > RTSAN_OPTIONS="suppressions=suppressions.supp" ./a.out
+ ...
+
+Suppressions specified in this file are one of two flavors.
+
+``function-name-matches`` suppresses reporting of any intercepted library call, or function marked ``[[clang::blocking]]`` by name. If, for instance, you know that ``malloc`` is real-time safe on your system, you can disable the check for it via ``function-name-matches:malloc``.
+
+``call-stack-contains`` suppresses reporting of errors in any stack that contains a string matching the pattern specified. For example, suppressing error reporting of any non-real-time-safe behavior in ``std::vector`` may be specified ``call-stack-contains:std::*vector``. You must include symbols in your build for this method to be effective, unsymbolicated stack traces cannot be matched. ``call-stack-contains`` has the highest run-time cost of any method of suppression.
+
+Patterns may be exact matches or are "regex-light" patterns, containing special characters such as ``^$*``.
+
Compile-time sanitizer detection
--------------------------------
``````````
</details>
https://github.com/llvm/llvm-project/pull/112727
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