7.3.6.27 Program Built with Foreign Tools and DLL Built with GCC/GNAT

In this case things are slightly more complex because it is not possible to start the main program and then break at the beginning to load the DLL and the associated DLL debugging information. It is not possible to break at the beginning of the program because there is no GDB debugging information, and therefore there is no direct way of getting initial control. This section addresses this issue by describing some methods that can be used to break somewhere in the DLL to debug it.

First suppose that the main procedure is named main (this is for example some C code built with Microsoft Visual C) and that there is a DLL named test.dll containing an Ada entry point named ada_dll.

The DLL (see Introduction to Dynamic Link Libraries (DLLs)) must have been built with debugging information (see GNAT -g option).

Debugging the DLL Directly

• * Find out the executable starting address

  $ objdump --file-header main.exe
  

  The starting address is reported on the last line. For example:

  main.exe:     file format pei-i386
  architecture: i386, flags 0x0000010a:
  EXEC_P, HAS_DEBUG, D_PAGED
  start address 0x00401010
  

• * Launch the debugger on the executable.

  $ gdb main.exe
  

• * Set a breakpoint at the starting address, and launch the program.

  $ (gdb) break *0x00401010
  $ (gdb) run
  

  The program will stop at the given address.

• * Set a breakpoint on a DLL subroutine.

  (gdb) break ada_dll.adb:45
  

  Or if you want to break using a symbol on the DLL, you need first to select the Ada language (language used by the DLL).

  (gdb) set language ada
  (gdb) break ada_dll
  

• * Continue the program.

  (gdb) cont
  

  This will run the program until it reaches the breakpoint that has been set. From that point you can use the standard way to debug a program as described in (Running and Debugging Ada Programs).

It is also possible to debug the DLL by attaching to a running process.

Attaching to a Running Process

With GDB it is always possible to debug a running process by attaching to it. It is possible to debug a DLL this way. The limitation of this approach is that the DLL must run long enough to perform the attach operation. It may be useful for instance to insert a time wasting loop in the code of the DLL to meet this criterion.

• * Launch the main program main.exe.

  $ main
  

• * Use the Windows `Task Manager' to find the process ID. Let’s say that the process PID for main.exe is 208.
• * Launch gdb.

  $ gdb
  

• * Attach to the running process to be debugged.

  (gdb) attach 208
  

• * Load the process debugging information.

  (gdb) symbol-file main.exe
  

• * Break somewhere in the DLL.

  (gdb) break ada_dll
  

• * Continue process execution.

  (gdb) cont
  

This last step will resume the process execution, and stop at the breakpoint we have set. From there you can use the standard approach to debug a program as described in Running and Debugging Ada Programs.