Re: [PATCH] Fix ctrl-c when debugging WOW64 processes

[Hannes Domani <ssbssa@yahoo.de>]

 Am Donnerstag, 17. September 2020, 22:00:29 MESZ hat Simon Marchi <simark@simark.ca> Folgendes geschrieben:

> On 2020-09-17 2:03 p.m., Hannes Domani via Gdb-patches wrote:
> > DebugBreakProcess starts a new thread in the target process with the
> > entry point DbgUiRemoteBreakin, where an int3 triggers a breakpoint
> > exception for gdb.
> >
> > But this uses DbgUiRemoteBreakin of the 64bit ntdll.dll even for
> > WOW64 processes.
> > It stops in 64bit code, Wow64GetThreadContext reports a wrong pc without
> > the int3, and gdb lets the target process continue.
> >
> > So this uses DbgUiRemoteBreakin of the 32bit ntdll.dll as the thread
> > entry point for WOW64 processes instead.
>
> Interesting.  Is there any reference somewhere that explains that things
> must be done this way when a 64 bit process is debugging a 32 bit
> process?

Sadly, I could find no real reference for this.
It took me quite a few hours to debug/understand this problem.


> In any case, the patch is OK, with the formatting nits below fixed.
>
> > @@ -1522,9 +1524,36 @@ ctrl_c_handler (DWORD event_type)
> >    if (!new_console && !attach_flag)
> >      return TRUE;
> >
> > -  if (!DebugBreakProcess (current_process_handle))
> > -    warning (_("Could not interrupt program.  "
> > -          "Press Ctrl-c in the program console."));
> > +#ifdef __x86_64__
> > +  if (wow64_process)
> > +    {
> > +      /* Call DbgUiRemoteBreakin of the 32bit ntdll.dll in the target process.
> > +    DebugBreakProcess would call the one of the 64bit ntdll.dll, which
> > +    can't be correctly handled by gdb.  */
> > +      if (!wow64_dbgbreak)
>
> wow64_dbgbreak == nullptr
>
>
> > +    {
> > +      CORE_ADDR addr;
> > +      if (!find_minimal_symbol_address ("ntdll!DbgUiRemoteBreakin",
> > +                        &addr, 0))
> > +        wow64_dbgbreak = (void *) addr;
> > +    }
> > +
> > +      if (wow64_dbgbreak)
>
>
> wow64_dbgbreak != nullptr

Pushed with these changes, thanks.


Hannes