Re: bug in gdb tty command on cygwin

Re: bug in gdb tty command on cygwin

[Steven O'Brien]

Chris Faylor wrote:
>[Reply-To set to gdb mailing list]
>On Sat, Jan 04, 2003 at 09:44:05AM +0000, Steven O'Brien wrote:
>>Hi
>>I submitted a patch to fix a bug in cygwin gdb to the gdb-patches list
>->see:
>>http://sources.redhat.com/ml/gdb-patches/2002-12/msg00761.html
>>
>>However, this did not attract any response. What is the next step in
>>getting this patch into gdb?
>
>Patience?

Thanks for your swift response Chris :)

>>With this patch I am able to build and run a fully functional anjuta
>IDE>on cygwin-xfree86. Without it anjuta's debugger will not work on
>cygwin.>I am sure that other X11 GUIs for gdb on cygwin would also
>benefit from>this patch.
>>
>>The patch moves one line of code in just one file that is only used in
>>the cygwin build; and code that is only invoked if the --tty option or
>>tty command are invoked.
>
>I saw your patch but since it invoked a "Huh?" response, it required
>some study.  I don't see any correlation between your description of
>the problem and your proposed patch.  I don't know why closing the tty
>later would cause the kind of problem you were talking about, so it
>isn't an obvious "plop it right in" kind of patch.
>
>cgf

You are right, the problem should not logically occur because of this.
However, the problem is real is is cured by my patch. In any case,
closing the tty after Create Process is logically incorrect, because the
inferior then inherits this fd which could concievably change its
behaviour. My patch therefore is a correction for an error in the gdb
code. As a bonus, the patch also fixes the broken gdb tty command, which
is what I need for cygwin-xfree86 anjuta.

After more testing, I have found that the problem does not occur when
the target tty is a windows console running bash. It does not matter
whether gdb is running in a console or pseudo-terminal. My testing
previously had used only rxvt (both X11 and native windows), xterm and
gnome-terminal, all of which cause the failure. I guess this might
indicate some problem with cygwin pty code. But the gdb tty command has
been broken for a long time, so its unlikely that the recent cygwin tty
changes are to blame.

Thanks again for looking at this,
Steven

Re: bug in gdb tty command on cygwin

[Christopher Faylor]

[Reply to set to mailing list - beware]
On Sat, Jan 04, 2003 at 10:00:48PM +0000, Steven O'Brien wrote:
>>>With this patch I am able to build and run a fully functional anjuta
>>IDE>on cygwin-xfree86. Without it anjuta's debugger will not work on
>>cygwin.>I am sure that other X11 GUIs for gdb on cygwin would also
>>benefit from>this patch.
>>>
>>>The patch moves one line of code in just one file that is only used in
>>>the cygwin build; and code that is only invoked if the --tty option or
>>>tty command are invoked.
>>
>>I saw your patch but since it invoked a "Huh?" response, it required
>>some study.  I don't see any correlation between your description of
>>the problem and your proposed patch.  I don't know why closing the tty
>>later would cause the kind of problem you were talking about, so it
>>isn't an obvious "plop it right in" kind of patch.
>
>You are right, the problem should not logically occur because of this.
>However, the problem is real is is cured by my patch. In any case,
>closing the tty after Create Process is logically incorrect, because the
>inferior then inherits this fd which could concievably change its
>behaviour. My patch therefore is a correction for an error in the gdb
>code. As a bonus, the patch also fixes the broken gdb tty command, which
>is what I need for cygwin-xfree86 anjuta.

I understand that there is an extra fd open.  I remember making a
conscious decision to keep it open and I really should have added a
comment about it because I don't remember why now.  Given the way cygwin
allocates ttys it is not necessarily a bad thing to keep an fd around
associated with the tty.  One reason, is that if the process closes
stdin/stdout/stderr and reopens the tty it may not get the tty that it
thinks it is getting.

Regardless, I'm never comfortable with patches that "seem to work fine
for me" when there is no explanation as to why.

Actually, the more I think about it, the more I think that the current
implementation could fail in strange ways due to process startup races
even with the current method for doing closes.

>After more testing, I have found that the problem does not occur when
>the target tty is a windows console running bash. It does not matter
>whether gdb is running in a console or pseudo-terminal. My testing
>previously had used only rxvt (both X11 and native windows), xterm and
>gnome-terminal, all of which cause the failure. I guess this might
>indicate some problem with cygwin pty code. But the gdb tty command has
>been broken for a long time, so its unlikely that the recent cygwin tty
>changes are to blame.

No, the gdb command hasn't been broken for a long time.  The tty command
wasn't implemented until 2002-09-13.  An official version of gdb.exe
which supported it was released on 2002-12-16.  I did test it repeatedly
in the console tty case and it seems to work fine.  I didn't think to
try it on rxvt, though.

cgf

bug in gdb tty command on cygwin

[Steven O'Brien]

Hi
I submitted a patch to fix a bug in cygwin gdb to the gdb-patches list -
see:
http://sources.redhat.com/ml/gdb-patches/2002-12/msg00761.html

However, this did not attract any response. What is the next step in
getting this patch into gdb?

With this patch I am able to build and run a fully functional anjuta IDE
on cygwin-xfree86. Without it anjuta's debugger will not work on cygwin.
I am sure that other X11 GUIs for gdb on cygwin would also benefit from
this patch.

The patch moves one line of code in just one file that is only used in
the cygwin build; and code that is only invoked if the --tty option or
tty command are invoked.

Thanks,
Steven

Re: bug in gdb tty command on cygwin

[Christopher Faylor]

[Reply-To set to gdb mailing list]
On Sat, Jan 04, 2003 at 09:44:05AM +0000, Steven O'Brien wrote:
>Hi
>I submitted a patch to fix a bug in cygwin gdb to the gdb-patches list -
>see:
>http://sources.redhat.com/ml/gdb-patches/2002-12/msg00761.html
>
>However, this did not attract any response. What is the next step in
>getting this patch into gdb?

Patience?

>With this patch I am able to build and run a fully functional anjuta IDE
>on cygwin-xfree86. Without it anjuta's debugger will not work on cygwin.
>I am sure that other X11 GUIs for gdb on cygwin would also benefit from
>this patch.
>
>The patch moves one line of code in just one file that is only used in
>the cygwin build; and code that is only invoked if the --tty option or
>tty command are invoked.

I saw your patch but since it invoked a "Huh?" response, it required some
study.  I don't see any correlation between your description of the problem
and your proposed patch.  I don't know why closing the tty later would cause
the kind of problem you were talking about, so it isn't an obvious "plop it
right in" kind of patch.

cgf