bug#63283: Emacs crash within fontset

[Seppo Ronkainen]

Your suggested patch successfully avoided the abort, great !

Where the abort would previously occur now instead the buffer renders all 
characters with four digit code point rectangular representations which I would 
consider preferable to an abort the entire emacs server session with thirty or 
so windows. Tested with visiting a large file emacs/src/xdisp.c and Emacs 
swapps back to render regular characters when text is scaled back. I would vote 
for your suggested fix, well done thank you !




Live long and prosper

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------- Original Message -------
On Sunday, May 7th, 2023 at 6:48 AM, Eli Zaretskii <eliz@gnu.org> wrote:


> > Date: Sat, 06 May 2023 22:36:35 +0000
> > From: Seppo Ronkainen sodr80@protonmail.com
> > Cc: 63283@debbugs.gnu.org
> > 
> > (gdb) frame 2
> > #2 0x00000055559233c4 in face_for_char (f=0x55564c8470, face=0x5556292b90, 
> > c=12302, pos=1, object=XIL(0)) at fontset.c:970
> > 970 eassert (fontset_id_valid_p (face->fontset));
> > (gdb) info locals
> > fontset = XIL(0)
> > rfont_def = XIL(0x555605b2b8)
> > charset = XIL(0x300effff7380)
> > face_id = 85
> > id = 1432078920
> > (gdb) print font_driver_list
> > $1 = (struct font_driver_list *) 0x55560d77e0
> > (gdb) print f->font_driver_list
> > $2 = (struct font_driver_list *) 0x5556274ae0
> > (gdb) frame 3
> > #3 0x00000055555bd308 in FACE_FOR_CHAR (f=0x55564c8470, face=0x5556292b90, 
> > character=12302, pos=1, object=XIL(0)) at dispextern.h:1911
> > (gdb) p face->font
> > $5 = (struct font *) 0x0
> > (gdb) p face->fontset
> > $6 = -1
> > (gdb) q
> 
> 
> Thanks. If you apply the patch below, does it avoid the abort?
> 
> > relevant commit ?
> > 3c0dda2663e38635163f0fd6c19748c6eba1c3c8
> > Avoid asserting for fontset validity before it is used
> 
> 
> No, I don't think so. We'd just abort earlier in that function.
> 
> diff --git a/src/fontset.c b/src/fontset.c
> index f196dee..e004cd9 100644
> --- a/src/fontset.c
> +++ b/src/fontset.c
> @@ -967,6 +967,9 @@ face_for_char (struct frame *f, struct face *face, int c,
> #endif
> }
> 
> + if (face->fontset < 0 && !face->font)
> 
> + return face->id;
> 
> +
> eassert (fontset_id_valid_p (face->fontset));
> 
> fontset = FONTSET_FROM_ID (face->fontset);
> 
> eassert (!BASE_FONTSET_P (fontset));