Re: [RFA/windows] Spurious "dll not found" error messages on x64-windows.

[Christopher Faylor <cgf-use-the-mailinglist-please@sourceware.org>]

On Thu, Feb 04, 2010 at 08:12:48AM +0400, Joel Brobecker wrote:
>When running 32bit programs on x64 windows, GDB produces the following
>error messages:
>
>        (gdb) start
>        Temporary breakpoint 1 at 0x4015ae: file simple_main.adb, line 4.
>        Starting program: C:\[...]/simple_main.exe
>        [New Thread 31464.0x8cd4]
> !!! -> Error: dll starting at 0x77a60000 not found.
> !!! -> Error: dll starting at 0x77650000 not found.
> !!! -> Error: dll starting at 0x77a60000 not found.
> !!! -> Error: dll starting at 0x77990000 not found.
>
>        Temporary breakpoint 1, simple_main () at simple_main.adb:4
>        4           simple.test_simple;
>
>This is something that was already discussed previously for gdbserver,
>where these events were not well handled and eventually lead to a crash:
>    http://www.sourceware.org/ml/gdb-patches/2010-02/msg00011.html
>
>A quick investigation showed that there were no dll-load-events that
>correspond to these base addresses.  A search on the net points at
>the WOW layer which interfaces between the 32bit and 64bit worlds.
>
>My first proposal is to silently ignore these spurious events during
>the startup phase.  We could probably refine this check by also verifying
>that we are running a 32bit exe on 64bit Windows.  But given that this
>error did not trigger in the past, I think that'd be overkill.  In fact,
>I don't think that ditching the error would be a big loss (we could turn
>it into a complaint if we want to be able to see it in special occasions).
>
>gdb/ChangeLog:
>
>        * windows-nat.c (handle_unload_dll): Disable unknown-dll error
>        during the inferior startup phase.
>
>Tested on x86_64-windows using a x86-windows compiler/debugger.
>OK to apply?
>
>Thanks,
>-- 
>Joel
>
>---
>diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
>index 2740366..4c2d1d8 100644
>--- a/gdb/windows-nat.c
>+++ b/gdb/windows-nat.c
>@@ -783,7 +783,16 @@ handle_unload_dll (void *dummy)
> 	return 1;
>       }
> 
>-  error (_("Error: dll starting at %s not found."),
>+  /* We did not find any DLL that was previously loaded at this address.
>+     This is normally an error.  However, we have observed that running
>+     32bit applications on x64 Windows causes us to receive 4 mysterious
>+     UNLOAD_DLL_DEBUG_EVENTs during the startup phase.  These events are
>+     apparently caused by the WOW layer (this is the interface between
>+     the 32bit and 64bit worlds).  Because of these events, we only report
>+     the error after the initialization phase is complete (there is not
>+     much data that we can use to identify these spurious events).  */
>+  if (windows_initialization_done)
>+    error (_("Error: dll starting at %s not found."),
> 	   host_address_to_string (lpBaseOfDll));
> 
>   return 0;

Sorry but, I don't think this right.  What's the point of issuing the
error after inferior startup?  I think it's only during startup that
something like this would be useful.

I think making the error a complaint makes more sense.

cgf