In 92eaad2 I made it possible to run

a debug session with only a remote path to the file you are debugging
using the SB API's. This patch makes it possible to do this using
target create --remote-file <some_path> without supplying a local file
as well.

Prior to this change we errored out saying that we haven't implemented
copying the binary back from the remote. I didn't implement the copy
back (in the case I'm interested in - iOS debugging - we don't
actually have a way for lldb to do that). This patch doesn't impede
doing that, I just didn't need it. I think for some object file
formats debugging w/o the binary file is hard because of what doesn't
get mapped in. I didn't try to arbitrate that, I'm assuming anybody
who has to do this knows what they are going to get.

If there's a connected platform that can check that the remote file
exists, it will do so, otherwise we trust the user's input - if it
isn't there the process launch is going to fail with no-such-file so
it will be pretty clear what went wrong.

Differential Revision: https://reviews.llvm.org/D124947

lldb/source/Commands/CommandObjectTarget.cpp

@@ -358,10 +358,29 @@ class CommandObjectTargetCreate : public CommandObjectParsed {
                 return false;
               }
             } else {
-              // make up a local file
-              result.AppendError("remote --> local transfer without local "
+              // If the remote file exists, we can debug reading that out of
+              // memory.  If the platform is already connected to an lldb-server
+              // then we can at least check the file exists remotely.  Otherwise
+              // we'll just have to trust that it will be there when we do
+              // process connect.
+              // I don't do this for the host platform because it seems odd to
+              // support supplying a remote file but no local file for a local
+              // debug session.
+              if (platform_sp->IsHost()) {
+                result.AppendError("Supply a local file, not a remote file, "
+                                   "when debugging on the host.");
+                return false;
+              }
+              if (platform_sp->IsConnected() && !platform_sp->GetFileExists(remote_file)) {
+                result.AppendError("remote --> local transfer without local "
                                  "path is not implemented yet");
-              return false;
+                return false;
+              }
+              // Since there's only a remote file, we need to set the executable
+              // file spec to the remote one.
+              ProcessLaunchInfo launch_info = target_sp->GetProcessLaunchInfo();
+              launch_info.SetExecutableFile(FileSpec(remote_file), true);
+              target_sp->SetProcessLaunchInfo(launch_info);
             }
           }
         } else {

lldb/test/API/functionalities/gdb_remote_client/TestNoLocalFile.py

@@ -12,7 +12,13 @@ class TestNoLocalFile(GDBRemoteTestBase):
     mydir = TestBase.compute_mydir(__file__)
 
     @skipIfXmlSupportMissing
-    def test(self):
+    def test_with_python(self):
+        self.do_test(False)
+    @skipIfXmlSupportMissing
+    def test_with_target_ceate(self):
+        self.do_test(True)
+
+    def do_test(self, use_target_create):
         self.absent_file = '/nosuch_dir/nosuch_subdir/nosuch_executable'
         self.a_packet_file = None
         class MyResponder(MockGDBServerResponder):
@@ -67,10 +73,19 @@ def qProcessInfo(self):
 
         error = lldb.SBError()
         self.server.responder = MyResponder(self)
-        target = self.dbg.CreateTarget(None, "x86_64-apple-macosx", "remote-macosx", False, error)
-        self.assertSuccess(error, "Made a valid target")
+        target = lldb.SBTarget()
+        if (use_target_create):
+            create_cmd = "target create --arch x86_64-apple-macosx --platform remote-macosx --remote-file {0}".format(self.absent_file)
+            self.runCmd(create_cmd)
+            target = self.dbg.GetSelectedTarget()
+            self.assertTrue(target.IsValid(), "Made a valid target")
+        else:
+            target = self.dbg.CreateTarget(None, "x86_64-apple-macosx", "remote-macosx", False, error)
+            self.assertSuccess(error, "Made a valid target")
+
         launch_info = target.GetLaunchInfo()
-        launch_info.SetExecutableFile(lldb.SBFileSpec(self.absent_file), True)
+        if (not use_target_create):
+            launch_info.SetExecutableFile(lldb.SBFileSpec(self.absent_file), True)
         flags = launch_info.GetLaunchFlags()
         flags |= lldb.eLaunchFlagStopAtEntry
         launch_info.SetLaunchFlags(flags)