Re: Display problems with non-ascii characters

[Kenichi Handa <handa@m17n.org>]

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In article <m2hc7fsfmf.fsf@kenny.sha-bang.de>, Sascha Wilde <wilde@sha-bang.de> writes:

> I'm not intending to be a pita, but this is still an issue and I think
> it should be further investigated and resolved.

Thank you for keeping on attacking this problem.  But...

> If I can help, by sending debugger info or the like please tell me what
> to do.

as the reported phenomenon is so mysterious that I can't
think of any good debugging strategy.  :-(

> On a second thought I think that my statement:
> > So It seems the problem might really be a strange X11 bug, which is
> > triggered by the new Emacs display code?

> is somewhat to much of an excuse:  The problem really only shows with
> recent Emacs, not with any other application where I'm using exactly the
> same fonts, nor with older (22) Emacsn.

> More additional information, I don't know if its useful but it might
> contain some hints for those who know the dirty details of Emacs
> display...  ;-)

> I noticed the following phenomenon (which is really an extended version
> of my observations from the last mail):

> I have two systems, A and B, and two users foo and bar, they both have
> access to the very same Emacs binary (over nfs) and they both can use
> the same X display (via ssh -X).
> My X-server runs an system A.

> 1. I start Emacs with -Q as user bar on system B and do my C-h H test.
>    No problem when changing the default font to terminus.
>    After that I quit Emacs.

> 2. I start Emacs as user foo on system A and do some work, until the
>    "vanished special chars" bug shows up.  I keep that Emacs running and
>    ...

> 3. ... start again Emacs -Q as bar on system B and do my C-h H test.
>    After changing the default font to terminus the umlauts are vanished
>    in this instance of Emacs, too!

>    Please note that the only thing the two Emacsn have in common is the
>    X Display, as they run on different hosts by different users.

> 4. Now: when I quit both Emacsn and restart at 1. the bug is gone again!

>    So it affects all Emacsn on the same display once it appeared, but it
>    "heals" again when all affected Emacsn are closed...

> Any ideas?  Insights?  Suggestions on how to proceed debugging this?

As far as I can't reproduce the problem, I think there's no
way other than you debug Emacs by gdb.

As you wrote:
----------------------------------------------------------------------
C-u C-x =  on the vanished `^[$(D)N^[(B' shows:
[...]
    x:-xos4-terminus-medium-r-normal--16-160-72-72-c-80-iso10646-1 (#xDF)
----------------------------------------------------------------------

Please find a way to reproduce the problem with a buffer
that contains only "^[$(D)N^[(B".  Then, run Emacs under gdb as this:

% cd .../src/emacs
% gdb emacs
(gdb) br xfont.c:833
(gdb) cond 3 len==1&& s->char2b.byte2==0xDF
(gdb) run

and repeat the above procedure.  Emacs should stop at line
841.  Then try this and see how screen changes:

(gdb) ff
(gdb) fin
(gdb) ff

See also emacs/etc/DEBUG.  It has many hints for debugging
Emacs with gdb.

---
Kenichi Handa
handa@ni.aist.go.jp