[RFA] windows-nat.c Cygwin save_context fix
Pierre Muller
muller@ics.u-strasbg.fr
Mon Sep 21 22:35:00 GMT 2009
> -----Message d'origine-----
> De : Christopher Faylor [mailto:cgf-use-the-mailinglist-
> please@sourceware.org]
> Envoyé : Tuesday, September 22, 2009 12:27 AM
> À : gdb-patches@sourceware.org; Pierre Muller
> Objet : Re: [RFA] windows-nat.c Cygwin save_context fix
>
> On Mon, Sep 21, 2009 at 05:14:57PM +0200, Pierre Muller wrote:
> > Cygwin has a way to give a "fake" context for
> >an exception using a OUTPUT_DEBUG_STRING_EVENT.
> >
> > While trying to debug some crashes inside cygwin dll,
> >I realized the the saved_context code has a problem.
> >
> > The saved context was correctly written to the thread_info
> >struct, but later overwritten by a call to GetThreadContext.
> >
> > After the cygwin special output_debug_string was correctly
> >converted into a context stored in saved_context.
> > The next call to do_windows_fetch_inferior_registers
> >then copied this context to the thread_info struct,
> >set the reload_context field to zero.
> >
> > But a later call to thread_rec() with get_context=1
> >can reset reload_context to one, if suspended field
> >is zero (this only happens if it is not the main thread).
> >
> > My patch fixes the problem by explicitly calling
> >SuspendThread for the threaded of the saved_context
> >if suspended is still zero at that point.
> >
> >
> >Pierre Muller
> >Pascal language support maintainer for GDB
> >
> >
> >
> >2009-09-21 Pierre Muller <muller@ics.u-strasbg.fr>
> >
> > * src/gdb/windows-nat.c (saved_threadid): New variable.
> > (do_windows_fetch_inferior_registers): Check for correct thread
> id
> > and force call to SuspendThread if needed.
> > (handle_output_debug_string): Set saved_threadid.
>
> I REALLY hate SuspendThread and am not likely to accept a patch which
> uses it as a solution.
I don't think that we really need to call SuspendThread,
in fact, I suspect the best would be to set suspended
to -1 as for main_threadid. I will try to check out if this also works.
> I don't really understand the scenario that you are talking about since
> I (obviously?) have no problems debugging SEGVs in cygwin. However,
I was trying to debug a home compiled expect
linked to 8.5.7 tcl library, that was call abort,
and the subsequent cygwin stackdump was segfaulting.
> would just removing the "have_saved_context = 0;" from
> do_windows_fetch_inferior_registers fix the problem?
But them we need to be really careful about to where
we should reset it to zero, otherwise we might end up
by still copying saved_context, even after having reran the debuggee, no?
Pierre
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