Runtime intercept tables#
Although most tools will want to leverage the callback or buffer tracing services for tracing the HIP, HSA, and ROCTx APIs, rocprofiler-sdk does provide access to the raw API dispatch tables. Each of the aforementioned APIs are designed similar to the following sample.
Dispatch Table Overview#
Forward Declaration of public C API function#
extern "C"
{
// forward declaration of public C API function
int
foo(int) __attribute__((visibility("default")));
}
Internal Implementation of API function#
namespace impl
{
int
foo(int val)
{
// real implementation
return (2 * val);
}
}
Dispatch Table Implementation#
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 above and below, 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#
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 is given an opportunity within impl::construct_dispatch_table()
to
save the original value(s) of the function pointers such as foo_fn
and install
it’s own function pointers in its place – this results in the public C API function foo
calling into the rocprofiler-sdk function pointer, which then in turn, calls the original
function pointer to impl::foo
(this is called “chaining”). Once rocprofiler-sdk
has made any necessary modifications to the dispatch table, tools which indicated
they also want access to the raw dispatch table via rocprofiler_at_intercept_table_registration
will be passed the pointer to the dispatch table.
Sample#
For a demo of dispatch table chaining, please see the samples/intercept_table
example in the
rocprofiler-sdk GitHub repository.