[clang] [NFC][rtsan] Docs of how to disable rtsan (PR #107707)

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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/107707.diff


1 Files Affected:

- (modified) clang/docs/RealtimeSanitizer.rst (+50) 


``````````diff
diff --git a/clang/docs/RealtimeSanitizer.rst b/clang/docs/RealtimeSanitizer.rst
index 799cd43509c6e6..7854cd3c0331a4 100644
--- a/clang/docs/RealtimeSanitizer.rst
+++ b/clang/docs/RealtimeSanitizer.rst
@@ -83,3 +83,53 @@ non-zero exit code.
     #13 0x00010230dd64 in main main.cpp:9
     #14 0x0001958960dc  (<unknown module>)
     #15 0x2f557ffffffffffc  (<unknown module>)
+
+Disabling
+---------
+
+In some circumstances, you may want to suppress RealtimeSanitizer violations in a specific scope.
+
+In C++, this is achieved via  ``__rtsan::ScopedDisabler``. Within the scope where the ``ScopedDisabler`` object is instantiated, all sanitizer-reported violations are suppressed. This suppression applies to the current scope as well as all invoked functions, including any functions called transitively. 
+
+.. code-block:: c++
+
+    #include <sanitizer/rtsan_interface.h>
+
+    void process(const std::vector<float>& buffer) [[clang::nonblocking]] {
+        {
+            __rtsan::ScopedDisabler d;
+            ...
+        }
+    }
+
+If RealtimeSanitizer is not enabled at compile time (i.e., the code is not compiled with the ``-fsanitize=realtime`` flag), the ``ScopedDisabler`` is compiled as a no-op.
+
+In C, you can use the ``__rtsan_disable()`` and ``rtsan_enable()`` functions to manually disable and re-enable RealtimeSanitizer checks. 
+
+.. code-block:: c++
+
+    #include <sanitizer/rtsan_interface.h>
+
+    int process(const float* buffer) [[clang::nonblocking]]
+    {
+        {
+            __rtsan_disable();
+
+            ...
+
+            __rtsan_enable();
+        }
+    }
+
+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, undefined behavior may result, potentially leaving the sanitizer permanently disabled for the rest of the program's execution.
+
+Compile-time sanitizer detection
+--------------------------------
+
+Clang provides the pre-processor macro ``__has_feature`` which may be used to detect if RealtimeSanitizer is enabled at compile-time.
+
+.. code-block:: c++
+
+    #if defined(__has_feature) && __has_feature(realtime_sanitizer)
+    ...
+    #endif

``````````

</details>


https://github.com/llvm/llvm-project/pull/107707