[debugserver] Initialize logging earlier in the startup sequence

[bulbazord]

Summary

Prior to setting up logging, we have uses of RNBLogSTDERR and
RNBLogSTDOUT. These macros will dump to STDERR and STDOUT respectively
if debugserver has a tty. Otherwise, it uses _DNBLog, which will do
nothing if a logging function hasn't been set up. For example, if you
specify a log file that cannot be opened for any reason and you don't
have a tty, you have 0 insight into what happened.

rdar://105473133

[jasonmolenda]

lldb/tools/debugserver/source/debugserver.cpp

1340–1341

Should this be moved out of this log_file != NULL block so that the logging flags are set based on -f value? Otherwise looks good to me.

[bulbazord]

lldb/tools/debugserver/source/debugserver.cpp

1340–1341

Good catch, that is indeed the case. I'll update this.

[bulbazord]

Moving second use of DNBSetLogMask outside of the log file block

lldb/tools/debugserver/source/debugserver.cpp

#endif
   // death,
   // we don't need no stinking SIGCHLD's...
 
   sigset_t sigset;
   sigemptyset(&sigset);
   sigaddset(&sigset, SIGCHLD);
   sigprocmask(SIG_BLOCK, &sigset, NULL);
 
+  // Set up DNB logging by default. If the user passes different log flags or a
+  // log file, these settings will be modified after processing the command line
+  // arguments.
+  auto log_callback = OsLogger::GetLogFunction();
+  if (log_callback) {
+    // if os_log() support is available, log through that.
+    DNBLogSetLogCallback(log_callback, nullptr);
+    DNBLog("debugserver will use os_log for internal logging.");
+  } else {
+    // Fall back to ASL support.
+    DNBLogSetLogCallback(ASLLogCallback, nullptr);
+    DNBLog("debugserver will use ASL for internal logging.");
+  }
+  DNBLogSetLogMask(/*log_flags*/ 0);
+
   g_remoteSP = std::make_shared<RNBRemote>();
 
   RNBRemote *remote = g_remoteSP.get();
   if (remote == NULL) {
     RNBLogSTDERR("error: failed to create a remote connection class\n");
     return -1;
   }
 
#endif
 
   remote->Context().SetDetachOnError(g_detach_on_error);
 
   remote->Initialize();
 
   // It is ok for us to set NULL as the logfile (this will disable any logging)
 
   if (log_file != NULL) {
+    DNBLog("debugserver is switching to logging to a file.");
     DNBLogSetLogCallback(FileLogCallback, log_file);
     // If our log file was set, yet we have no log flags, log everything!
     if (log_flags == 0)
       log_flags = LOG_ALL | LOG_RNB_ALL;
-
-    DNBLogSetLogMask(log_flags);
-  } else {
-    // Enable DNB logging
-
-    // if os_log() support is available, log through that.
-    auto log_callback = OsLogger::GetLogFunction();
-    if (log_callback) {
-      DNBLogSetLogCallback(log_callback, nullptr);
-      DNBLog("debugserver will use os_log for internal logging.");
-    } else {
-      // Fall back to ASL support.
-      DNBLogSetLogCallback(ASLLogCallback, NULL);
-      DNBLog("debugserver will use ASL for internal logging.");
-    }
-    DNBLogSetLogMask(log_flags);
-  }
 
   if (DNBLogEnabled()) {
     for (i = 0; i < argc; i++)
       DNBLogDebug("argv[%i] = %s", i, argv[i]);
   }
 
   // as long as we're dropping remotenub in as a replacement for gdbserver,
   // explicitly note that this is not gdbserver.