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projects/rocprofiler-sdk/source/docs/api-reference/intercept_table.rst

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+
+.. meta::
+    :description: ROCprofiler-SDK is a tooling infrastructure for profiling general-purpose GPU compute applications running on the ROCm software
+    :keywords: ROCprofiler-SDK API reference, ROCprofiler-SDK intercept table, Intercept table API
+
+.. _runtime-intercept-tables:
+
+Runtime intercept tables
+=========================
+
+While tools commonly leverage the callback or buffer tracing services for tracing the HIP, HSA, and ROCTx
+APIs, ROCprofiler-SDK also provides access to the raw API dispatch tables.
+
+Forward declaration of public C API function
+----------------------------------------------
+
+All the aforementioned APIs are designed similar to the following sample:
+
+.. code-block:: cpp
+
+    extern "C"
+    {
+    // forward declaration of public C API function
+    int
+    foo(int) __attribute__((visibility("default")));
+    }
+
+Internal implementation of API function
+-----------------------------------------
+
+.. code-block:: cpp
+
+    namespace impl
+    {
+    int
+    foo(int val)
+    {
+        // real implementation
+        return (2 * val);
+    }
+    }
+
+Dispatch table implementation
+-------------------------------
+
+.. code-block:: cpp
+
+    namespace impl
+    {
+    struct dispatch_table
+    {
+        int (*foo_fn)(int) = nullptr;
+    };
+
+    // Invoked once: populates the dispatch_table with function pointers to implementation
+    dispatch_table*&
+    construct_dispatch_table()
+    {
+        static dispatch_table* tbl = new dispatch_table{};
+        tbl->foo_fn                = impl::foo;
+
+        // In between, ROCprofiler-SDK gets passed the pointer
+        // to the dispatch table and has the opportunity to wrap the function
+        // pointers for interception
+
+        return tbl;
+    }
+
+    // Constructs dispatch table and stores it in static variable
+    dispatch_table*
+    get_dispatch_table()
+    {
+        static dispatch_table*& tbl = construct_dispatch_table();
+        return tbl;
+    }
+    }  // namespace impl
+
+Implementation of public C API function
+-----------------------------------------
+
+.. code-block:: cpp
+
+    extern "C"
+    {
+    // implementation of public C API function
+    int
+    foo(int val)
+    {
+        return impl::get_dispatch_table()->foo_fn(val);
+    }
+    }
+
+Dispatch table chaining
+-------------------------
+
+ROCprofiler-SDK can save the original values of the function pointers such as ``foo_fn`` in ``impl::construct_dispatch_table()`` and install its own function pointers in its place. This results in the public C API function ``foo`` calling into the ROCprofiler-SDK function pointer, which in turn, calls the original function pointer to ``impl::foo``. This phenomenon is named chaining. Once ROCprofiler-SDK
+makes necessary modifications to the dispatch table, tools requesting access to the raw dispatch table via ``rocprofiler_at_intercept_table_registration`` are provided the pointer to the dispatch table.
+
+For examples on dispatch table chaining, see `samples/intercept_table <https://github.com/ROCm/rocprofiler-sdk/tree/amd-staging/samples/intercept_table>`_.