From c52a98dba20b37236fbf6c20ca07271fa442cada Mon Sep 17 00:00:00 2001
From: Martin <laz.git@mfriebe.de>
Date: Sun, 22 Jun 2025 15:31:05 +0200
Subject: [PATCH] FpDebug: Fix attaching to a process, if the project does not
 provide the filename of the (host) executable. Issue #41201

(cherry picked from commit 7f0a0f7ea64ec1589f7e8a452fc6b3230c041543)
---
 components/fpdebug/fpdbgcontroller.pas        | 37 +++++++++++++------
 .../lazdebuggerfp/fpdebugdebugger.pas         | 21 ++++++-----
 2 files changed, 38 insertions(+), 20 deletions(-)

diff --git a/components/fpdebug/fpdbgcontroller.pas b/components/fpdebug/fpdbgcontroller.pas
index 35b4215372..137b685a1f 100644
--- a/components/fpdebug/fpdbgcontroller.pas
+++ b/components/fpdebug/fpdbgcontroller.pas
@@ -305,6 +305,7 @@ type
     procedure SetParams(AValue: TStringList);
 
     procedure CheckExecutableAndLoadClasses(out ATargetInfo: TTargetDescriptor);
+    procedure InitForDefaultTargetAndLoadClasses(out ATargetInfo: TTargetDescriptor);
   protected
     FMainProcess: TDbgProcess;
     FCurrentProcess: TDbgProcess;
@@ -1554,6 +1555,13 @@ begin
   FOsDbgClasses := FpDbgClasses.GetDbgProcessClass(ATargetInfo);
 end;
 
+procedure TDbgController.InitForDefaultTargetAndLoadClasses(out ATargetInfo: TTargetDescriptor);
+begin
+  ATargetInfo := hostDescriptor;
+
+  FOsDbgClasses := FpDbgClasses.GetDbgProcessClass(ATargetInfo);
+end;
+
 procedure TDbgController.SetExecutableFilename(const AValue: string);
 begin
   if assigned(FMainProcess) then
@@ -2163,19 +2171,26 @@ begin
   Result := nil;
   assert(FMainProcess = nil, 'TDbgController.CreateDbgProcess: FMainProcess = nil');
 
-  if FExecutableFilename = '' then begin
-    DebugLn(DBG_WARNINGS, 'No filename given to execute.');
-    FLastError := CreateError(fpInternalErr, ['No filename given to execute.']);
-    Exit;
-  end;
-  if not FileExists(FExecutableFilename) then begin
-    DebugLn(DBG_WARNINGS, 'File %s does not exist.',[FExecutableFilename]);
-    FLastError := CreateError(fpInternalErr, ['File does not exist: ' + FExecutableFilename]);
-    Exit;
+  if AttachToPid = 0 then begin
+    if FExecutableFilename = '' then begin
+      DebugLn(DBG_WARNINGS, 'No filename given to execute.');
+      FLastError := CreateError(fpInternalErr, ['No filename given to execute.']);
+      Exit;
+    end;
+    if not FileExists(FExecutableFilename) then begin
+      DebugLn(DBG_WARNINGS, 'File %s does not exist.',[FExecutableFilename]);
+      FLastError := CreateError(fpInternalErr, ['File does not exist: ' + FExecutableFilename]);
+      Exit;
+    end;
+
+    // Get exe info, load classes
+    CheckExecutableAndLoadClasses(TargetDescriptor);
+  end
+  else begin
+    // Attach, get debug classes for the host system
+    InitForDefaultTargetAndLoadClasses(TargetDescriptor);
   end;
 
-  // Get exe info, load classes
-  CheckExecutableAndLoadClasses(TargetDescriptor);
   if not Assigned(OsDbgClasses) then begin
     DebugLn(DBG_WARNINGS, 'Error - No support registered for debug target');
     FLastError := CreateError(fpInternalErr, ['Unsupported target for file: ' + FExecutableFilename+'.'#13#10 +
diff --git a/components/lazdebuggers/lazdebuggerfp/fpdebugdebugger.pas b/components/lazdebuggers/lazdebuggerfp/fpdebugdebugger.pas
index 6438129e9e..f8305bb6fb 100644
--- a/components/lazdebuggers/lazdebuggerfp/fpdebugdebugger.pas
+++ b/components/lazdebuggers/lazdebuggerfp/fpdebugdebugger.pas
@@ -4157,7 +4157,19 @@ begin
     {$ifdef windows}
     FDbgController.ForceNewConsoleWin:=TFpDebugDebuggerProperties(GetProperties).ForceNewConsole;
     {$endif windows}
+
+    FDbgController.AttachToPid := 0;
+    if ACommand = dcAttach then begin
+      FDbgController.AttachToPid := StrToIntDef(String(AParams[0].VAnsiString), 0);
+      Result := FDbgController.AttachToPid <> 0;
+      if not Result then begin
+        FileName := '';
+        Exit;
+      end;
+    end;
+
     // Check if CreateDbgProcess returns a valid TDbgProcess
+//    if ACommand <> dcAttach then begin
     if Assigned(FDbgController.CurrentProcess) then begin
       FDbgController.CurrentProcess.Config.UseConsoleWinPos    := FUseConsoleWinPos;
       FDbgController.CurrentProcess.Config.UseConsoleWinSize   := FUseConsoleWinSize;
@@ -4175,15 +4187,6 @@ begin
 
       FDbgController.CurrentProcess.Config.BreakpointSearchMaxLines := TFpDebugDebuggerProperties(GetProperties).BreakpointSearchMaxLines;
 
-      FDbgController.AttachToPid := 0;
-      if ACommand = dcAttach then begin
-        FDbgController.AttachToPid := StrToIntDef(String(AParams[0].VAnsiString), 0);
-        Result := FDbgController.AttachToPid <> 0;
-        if not Result then begin
-          FileName := '';
-          Exit;
-        end;
-      end;
       FWorkQueue.Clear;
       FWorkQueue.ThreadCount := 1;
       {$IFDEF FPDEBUG_THREAD_CHECK} CurrentFpDebugThreadIdForAssert := FWorkQueue.Threads[0].ThreadID;{$ENDIF}