[llvm-jitlink] Fix use of getaddrinfo(3) when connecting remote executor via TCP socket

[sgraenitz]

Summary

Since llvm-jitlink moved from gethostbyname to getaddrinfo in D95477, it seems to no longer connect to llvm-jitlink-executor via TCP. I can reproduce this behavior on both, Debian 10 and macOS 10.15.7:

> llvm-jitlink-executor listen=localhost:10819
--
> llvm-jitlink --oop-executor-connect=localhost:10819 /path/to/obj.o
Failed to resolve localhost:10819

[sgraenitz]

The patch proposed here is a minimal fix. I am eager to streamline the code and add better error messages in a follow-up commit.

llvm/tools/llvm-jitlink/llvm-jitlink.cpp

707

This caused the getaddrinfo failure below.

722

We can pass the obtained AI structs to socket directly, but they might vary from entry to entry.

724

This caused a segfault in any second iteration. Not sure under which conditions the AI output memory is writable.

[sgraenitz]

Unfortunately, we seem to have no test coverage for this code. My last take was that LIT doesn't exactly make it easy to run client and server concurrently. Is that still the case or could we do it somehow differently?
I had to take a detailed look into this code now anyway, so I could just as well add a test case.

[rzurob]

LGTM

llvm/tools/llvm-jitlink/llvm-jitlink.cpp

if (PortStr.getAsInteger(10, Port))
     return make_error<StringError>("port number " + PortStr +
                                        " is not a valid integer",
                                    inconvertibleErrorCode());
 
   addrinfo *AI;
   addrinfo Hints{};
   Hints.ai_family = AF_INET;
   Hints.ai_socktype = SOCK_STREAM;
-  Hints.ai_protocol = PF_INET;
   Hints.ai_flags = AI_NUMERICSERV;
-  if (getaddrinfo(HostName.c_str(), PortStr.str().c_str(), &Hints, &AI) != 0)
-    return make_error<StringError>("Failed to resolve " + HostName + ":" +
-                                       Twine(Port),
+  if (int EC =
+          getaddrinfo(HostName.c_str(), PortStr.str().c_str(), &Hints, &AI))
+    return make_error<StringError>(formatv("Failed to resolve {0}:{1} ({2})",
+                                           HostName, Port, gai_strerror(EC)),
                                    inconvertibleErrorCode());
 
-  int SockFD = socket(PF_INET, SOCK_STREAM, 0);
-  sockaddr_in ServAddr;
-  memset(&ServAddr, 0, sizeof(ServAddr));
-  ServAddr.sin_family = PF_INET;
-  ServAddr.sin_port = htons(Port);
-
   // getaddrinfo returns a list of address structures.  Go through the list
   // to find one we can connect to.
+  int SockFD;
   int ConnectRC = -1;
   for (addrinfo *Server = AI; Server; Server = Server->ai_next) {
-    memmove(&Server->ai_addr, &ServAddr.sin_addr.s_addr, Server->ai_addrlen);
-    ConnectRC = connect(SockFD, reinterpret_cast<sockaddr *>(&ServAddr),
-                        sizeof(ServAddr));
+    // If socket fails, maybe it's because the address family is not supported.
+    // Skip to the next addrinfo structure.
+    if ((SockFD = socket(AI->ai_family, AI->ai_socktype, AI->ai_protocol)) < 0)
+      continue;
+
+    ConnectRC = connect(SockFD, Server->ai_addr, Server->ai_addrlen);
     if (ConnectRC == 0)
       break;
+
+    close(SockFD);
   }
   freeaddrinfo(AI);
   if (ConnectRC == -1)
     return make_error<StringError>("Failed to connect to " + HostName + ":" +
                                        Twine(Port),
                                    inconvertibleErrorCode());
 
   auto SSP = std::make_shared<SymbolStringPool>();