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

[jhuber6]

Summary

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

[lntue]

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

20

Can you add a direct dependency to libc.src.__support.RPC.rpc_client instead of relying on its transitive dependency via crt1?

[jhuber6]

Adding dependency on RPC directly.

[lntue]

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

20

The first lambda doesn't need to capture-by-reference.

libc/utils/gpu/loader/Server.h

47

This lambda doesn't need capture-by-reference.

51–52

Same with this one.

[jhuber6]

Addressing comments

[jhuber6]

Add port.close() after removing buggy RAII.

libc/src/__support/RPC/rpc.h

 namespace __llvm_libc {
 namespace rpc {
 
 /// A list of opcodes that we use to invoke certain actions on the server.
 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.
 struct alignas(64) Buffer {
   uint8_t data[62];
   uint16_t opcode;
 };
 static_assert(sizeof(Buffer) == 64, "Buffer size mismatch");

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

 add_custom_target(libc-startup-tests)
 add_dependencies(libc-integration-tests libc-startup-tests)
 
 add_integration_test(
   startup_args_test
   SUITE libc-startup-tests
   SRCS
     args_test.cpp
   ARGS
     1 2 3
   ENV
     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

+//===-- 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

case __llvm_libc::rpc::Opcode::PRINT_TO_STDERR: {
     break;
   }
   case __llvm_libc::rpc::Opcode::EXIT: {
     port->recv([](__llvm_libc::rpc::Buffer *buffer) {
       exit(reinterpret_cast<uint32_t *>(buffer->data)[0]);
     });
     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;
   }
   port->close();
 }
 #endif