[libc] Add a test to directly stimulate the RPC interface

Currently, the RPC interface with the loader is only tested if the other
tests fail. This test adds a direct test that runs a simple integer
increment over the RPC handshake 10000 times.

Depends on https://reviews.llvm.org/D148288

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D148342

libc/src/__support/RPC/rpc.h

@@ -34,6 +34,7 @@ enum Opcode : uint16_t {
   NOOP = 0,
   PRINT_TO_STDERR = 1,
   EXIT = 2,
+  TEST_INCREMENT = 3,
 };
 
 /// A fixed size channel used to communicate between the RPC client and server.

libc/test/integration/startup/gpu/CMakeLists.txt

@@ -12,3 +12,12 @@ add_integration_test(
     FRANCE=Paris
     GERMANY=Berlin
 )
+
+add_integration_test(
+  startup_rpc_test
+  SUITE libc-startup-tests
+  SRCS
+    rpc_test.cpp
+  DEPENDS
+    libc.src.__support.RPC.rpc_client
+)

libc/test/integration/startup/gpu/rpc_test.cpp

@@ -0,0 +1,34 @@
+//===-- Loader test to check the RPC interface with the loader ------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/RPC/rpc_client.h"
+#include "test/IntegrationTest/test.h"
+
+using namespace __llvm_libc;
+
+static void test_add_simple() {
+  constexpr int num_additions = 10000;
+  uint64_t cnt = 0;
+  for (int i = 0; i < num_additions; ++i) {
+    rpc::Port port = rpc::client.open(rpc::TEST_INCREMENT);
+    port.send_and_recv(
+        [=](rpc::Buffer *buffer) {
+          reinterpret_cast<uint64_t *>(buffer->data)[0] = cnt;
+        },
+        [&](rpc::Buffer *buffer) {
+          cnt = reinterpret_cast<uint64_t *>(buffer->data)[0];
+        });
+    port.close();
+  }
+  ASSERT_TRUE(cnt == num_additions && "Incorrect sum");
+}
+
+TEST_MAIN(int argc, char **argv, char **envp) {
+  test_add_simple();
+  return 0;
+}

libc/utils/gpu/loader/Server.h

@@ -42,6 +42,12 @@ void handle_server() {
     });
     break;
   }
+  case __llvm_libc::rpc::Opcode::TEST_INCREMENT: {
+    port->recv_and_send([](__llvm_libc::rpc::Buffer *buffer) {
+      reinterpret_cast<uint64_t *>(buffer->data)[0] += 1;
+    });
+    break;
+  }
   default:
     port->recv([](__llvm_libc::rpc::Buffer *) { /* no-op */ });
     return;