Re: [PATCH 31/34 v1.2] Windows gdb+gdbserver: Check whether DBG_REPLY_LATER is available

[Hannes Domani <ssbssa@yahoo.de>]

 Am Mittwoch, 8. Mai 2024 um 23:34:25 MESZ hat Pedro Alves <pedro@palves.net> Folgendes geschrieben:

> On 2024-05-08 13:45, Eli Zaretskii wrote:
>
> >> However, I found out that we can find the Windows major/minor/build in
> >> the KUSER_SHARED_DATA structure, which defines the layout of a data
> >> area that the kernel places at a pre-set address for sharing with
> >> user-mode software:
> >>
> >>  https://www.geoffchappell.com/studies/windows/km/ntoskrnl/structs/kuser_shared_data/index.htm
> >>
> >> The Windows major/minor/build version retrieved using that method
> >> bypasses the manifest stuff, it actually gets you the real OS version
> >> numbers.  That is what this patch is using.
> >
> > ...do we really need to do this via a version-check?  Can't we instead
> > just call ContinueDebugEvent and if it fails, consider DBG_REPLY_LATER
> > unsupported?  (If calling ContinueDebugEvent with that flag on older
> > versions of Windows causes an exception, we could use try/catch.)  If
> > this works, it is a more reliable way to test, IMO and IME.  I think
> > we should prefer that to poking kernel data structures.
>
> We need to know whether DBG_REPLY_LATER will work before starting the inferior.
> And we can only call ContinueDebugEvent after starting some inferior, and
> after the kernel returns an event for it via WaitForDebugEvent.

Looks like just trying to call ContinueDebugEvent is possible after all.

#include <windows.h>
#include <stdio.h>

#ifndef DBG_REPLY_LATER
#define DBG_REPLY_LATER 0x40010001
#endif

int main()
{
  if (!ContinueDebugEvent(0, 0, DBG_REPLY_LATER))
    printf("error: 0x%lx\n", GetLastError());

  return 0;
}

On Win10 this gives me error 0x6 (ERROR_INVALID_HANDLE), and on Win7 it
gives me error 0x57 (ERROR_INVALID_PARAMETER).


Hannes