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bug#10164: 24.0.91; Instant crash enabling linum-mode
From: |
Eli Zaretskii |
Subject: |
bug#10164: 24.0.91; Instant crash enabling linum-mode |
Date: |
Wed, 30 Nov 2011 08:54:41 -0500 |
> From: Dan Nicolaescu <dann@gnu.org>
> Cc: Tim Crews <tim.crews@code-affinity.com>, 10164@debbugs.gnu.org
> Date: Wed, 30 Nov 2011 07:52:40 -0500
>
> Eli Zaretskii <eliz@gnu.org> writes:
>
> >> Date: Tue, 29 Nov 2011 19:05:20 -0700
> >> From: Tim Crews <tim.crews@code-affinity.com>
> >>
> >> Start Emacs with runemacs -Q --no-init-file
> >> C-x C-f foo.txt
> >> M-x linum-mode
> >> (Emacs doesn't crash yet)
> >> Type anything. Emacs instantly crashes.
> >
> > Arrgh! This is GCC 4.6.x "as-is" code reordering in action. Emacs
> > crashes here:
> >
> > xassert (!row->enabled_p
> > || row->mode_line_p
> > || verify_row_hash (row));
> >
> > Evidently, it calls verify_row_hash before it tests row->mode_line_p.
>
> Are you sure?
How else can I explain this display from GDB:
(gdb) prow
y=0 x=0 pwid=673 a+d=12+4=16 phys=12+4=16 vis=16
used=(LMargin=0,Text=84,RMargin=0) Hash=263825844
start=0 end=0 ENA MODEL
? MODEL says that this row has its mode_line_p flag set.
Just to be sure, I ran the recipe again under GDB, setting a
breakpoint inside verify_row_hash thusly:
(gdb) break verify_row_hash if row->mode_line_p != 0
and sure enough, it breaks as soon as I turn on linum-mode, with ROW
that shows the glyphs in the mode line.
> Without interprocedural analysis the compiler cannot know
> that `verify_row_hash' does not alter row->enabled_p, so it cannot
> change the evaluation order.
I don't know. Maybe GCC does perform such an analysis. Or maybe it
decides that the result of this comparison in verify_row_hash:
row->hash == row_hash (row)
will not change even if row_hash does modify its argument ROW. Or
maybe it's a bug in GCC.
bug#10164: 24.0.91; Instant crash enabling linum-mode, Eli Zaretskii, 2011/11/30
- bug#10164: 24.0.91; Instant crash enabling linum-mode, Juanma Barranquero, 2011/11/30
- bug#10164: 24.0.91; Instant crash enabling linum-mode, Eli Zaretskii, 2011/11/30
- Message not available
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- bug#10164: 24.0.91; Instant crash enabling linum-mode, Eli Zaretskii, 2011/11/30
- bug#10164: 24.0.91; Instant crash enabling linum-mode, Chong Yidong, 2011/11/30
- bug#10164: 24.0.91; Instant crash enabling linum-mode, Chong Yidong, 2011/11/30
- bug#10164: 24.0.91; Instant crash enabling linum-mode, Juanma Barranquero, 2011/11/30