GNU bug report logs - #77478
Fixes a crash in the Haiku font driver for daemon mode

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From: Eli Zaretskii <eliz <at> gnu.org>
To: luangruo <at> yahoo.com
Cc: kyle <at> ambroffkao.com, 77478 <at> debbugs.gnu.org
Subject: bug#77478: Fixes a crash in the Haiku font driver for daemon mode
Date: Sat, 26 Apr 2025 14:34:52 +0300

Ping!  Po Lu, any suggestions or comments?

> Cc: 77478 <at> debbugs.gnu.org
> Date: Sat, 12 Apr 2025 14:35:17 +0300
> From: Eli Zaretskii <eliz <at> gnu.org>
> 
> > Date: Thu, 03 Apr 2025 07:10:53 +0000
> > From: "Kyle Ambroff-Kao" <kyle <at> ambroffkao.com>
> > 
> > This fixes double-free bug in Emacs daemon mode on Haiku. To reproduce:
> > 
> > 1. Start emacs with "emacs --daemon"
> > 2. Create a new frame with "emacsclient -c" and then close it.
> > 3. Create a new frame with "emacsclient -c"
> > 
> > Step 3 will cause the Emacs daemon to crash.
> > 
> >   KERN: debug_server: Thread 3616 entered the debugger: Debugger call:
> >   `tried to free 0xb960bc9fd0 which points at page 232 which is not an
> >   allocation first page'
> > 
> > The backtrace from Emacs:
> >    heap_free(void*) + 0x35 
> >    BFont_close + 0x4d 
> >    haikufont_close(font*) + 0x29 (/Code/emacs/src/haikufont.c:893)
> >    sweep_vectors(void) + 0x1af (/Code/emacs/src/alloc.c:3242)
> >    garbage_collect(void) + 0x7b3 (/Code/emacs/src/alloc.c:7247)
> >    Ffuncall(ptrdiff_t, Lisp_Object*) + 0x194 (/Code/emacs/src/eval.c:3084)
> >    internal_condition_case_n(*, ptrdiff_t, Lisp_Object*, Lisp_Object, *)
> >    + 0x6c (/Code/emacs/src/eval.c:1699)
> >    safe_funcall(ptrdiff_t, Lisp_Object*) + 0x50 (/Code/emacs/src/eval.c:3114)
> >    map_keymap_canonical(Lisp_Object,map_keymap_function_t,Lisp_Object,void*)
> >    + 0x2b (/Code/emacs/src/keymap.c:608)
> >    ...
> > 
> > It appears that the BFont has already been closed. I think that the
> > driver is holding on to the pointer to the freed BFont
> > (into->be_font). This patch addresses this by setting be_font to NULL so
> > that this pointer will not be freed again.
> > 
> > The same thing applies to info->metrics and info->glyphs, since just
> > making this change to be_font wasn't enough to avoid crashes.
> > 
> > With this patch I can open and close as many frames as I want without
> > crashing.
> > 
> > I don't totally understand the interactions here, and I see there are
> > similar bugs in other font drivers with different workarounds. For
> > example, in Bug#16069 which I found from xfont.c:xfont_close, it seems
> > like there is an attempt to just not free the fonts when GC is invoked.
> > 
> > I think the solution in this patch seems a little simpler, but possibly
> > means that the fonts are initialized every time the frame count goes
> > from 0 to 1 or more instead of just once for the life of the daemon.
> 
> Po Lu, any suggestions or comments?
> 
> 
> 
> 

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