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Fix undefined behavior when fetching glyphs from the display vector.

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You can trigger this rather obscure bug by enabling selective display
if the second glyph in its display vector has an invalid face.  For
example, evaluate

(set-display-table-slot standard-display-table
                        'selective-display [?A (?B . invalid)])

and then enable selective display.

* src/xdisp.c (next_element_from_display_vector): Check whether next
glyph code is valid before accessing it.
This commit is contained in:
Philipp Stephani 2020-11-09 22:14:39 +01:00
parent 78e1646bf7
commit 109eb1e7e2
1 changed files with 3 additions and 3 deletions
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6
src/xdisp.c
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@ -8221,10 +8221,10 @@ next_element_from_display_vector (struct it *it)
next_face_id = it->dpvec_face_id;
else
{
int lface_id =
GLYPH_CODE_FACE (it->dpvec[it->current.dpvec_index + 1]);
Lisp_Object gc = it->dpvec[it->current.dpvec_index + 1];
int lface_id = GLYPH_CODE_P (gc) ? GLYPH_CODE_FACE (gc) : 0;
if (lface_id > 0)
if (lface_id > 0)
next_face_id = merge_faces (it->w, Qt, lface_id,
it->saved_face_id);
}