From: Paul Eggert <eggert@cs.ucla.edu>
To: Eli Zaretskii <eliz@gnu.org>
Cc: emacs-devel@gnu.org
Subject: Re: FACE_FROM_ID vs FACE_OPT_FROM_ID
Date: Fri, 24 Jun 2016 02:23:17 +0200 [thread overview]
Message-ID: <576C7D75.4070401@cs.ucla.edu> (raw)
In-Reply-To: <83d1n73c5z.fsf@gnu.org>
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On 06/23/2016 10:03 PM, Eli Zaretskii wrote:
> What was the GCC 6.1 complaint that led you to this change?
Diagnostics like this one (there were quite a few):
> xdisp.c: In function 'fill_image_glyph_string':
> xdisp.c:24916:20: error: potential null pointer dereference
> [-Werror=null-dereference]
> s->font = s->face->font;
> ~~~~~~~^~~~~~
The problem being that s->face was set from FACE_FROM_ID, which (before
the change) might return a null pointer.
The intent is that FACE_FROM_ID returns a face (a non-null pointer),
whereas FACE_OPT_FROM_ID returns a face option (either a face or a null
pointer). Similarly for IMAGE_FROM_ID. I installed the attached patch to
try to make this clearer.
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From b3ef03f646c8fb3dc6d55a8ed0134b6963243f86 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Fri, 24 Jun 2016 02:19:13 +0200
Subject: [PATCH] Clarify intent of FACE_FROM_ID and IMAGE_FROM_ID
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
* src/dispextern.h (FACE_OPT_FROM_ID): Don’t use FACE_FROM_ID,
since it is intended to be used only when it returns a non-null
pointer, and here the pointer might be null.
(IMAGE_OPT_FROM_ID): Don’t use IMAGE_FROM_ID, for similar reasons.
---
src/dispextern.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/src/dispextern.h b/src/dispextern.h
index d0fc3b2..08dcd89 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -1812,7 +1812,7 @@ struct face_cache
bool_bf menu_face_changed_p : 1;
};
-/* Return a pointer to the cached face with ID on frame F. */
+/* Return a non-null pointer to the cached face with ID on frame F. */
#define FACE_FROM_ID(F, ID) \
(eassert (UNSIGNED_CMP (ID, <, FRAME_FACE_CACHE (F)->used)), \
@@ -1823,7 +1823,7 @@ struct face_cache
#define FACE_OPT_FROM_ID(F, ID) \
(UNSIGNED_CMP (ID, <, FRAME_FACE_CACHE (F)->used) \
- ? FACE_FROM_ID (F, ID) \
+ ? FRAME_FACE_CACHE (F)->faces_by_id[ID] \
: NULL)
/* True if FACE is suitable for displaying ASCII characters. */
@@ -3093,7 +3093,7 @@ struct image_cache
};
-/* A pointer to the image with id ID on frame F. */
+/* A non-null pointer to the image with id ID on frame F. */
#define IMAGE_FROM_ID(F, ID) \
(eassert (UNSIGNED_CMP (ID, <, FRAME_IMAGE_CACHE (F)->used)), \
@@ -3104,7 +3104,7 @@ struct image_cache
#define IMAGE_OPT_FROM_ID(F, ID) \
(UNSIGNED_CMP (ID, <, FRAME_IMAGE_CACHE (F)->used) \
- ? IMAGE_FROM_ID (F, ID) \
+ ? FRAME_IMAGE_CACHE (F)->images[ID] \
: NULL)
/* Size of bucket vector of image caches. Should be prime. */
--
2.5.5
next prev parent reply other threads:[~2016-06-24 0:23 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-23 20:03 FACE_FROM_ID vs FACE_OPT_FROM_ID Eli Zaretskii
2016-06-24 0:23 ` Paul Eggert [this message]
2016-06-24 8:49 ` Eli Zaretskii
2016-06-24 9:27 ` Paul Eggert
2016-06-24 9:57 ` Eli Zaretskii
2016-06-24 10:00 ` Eli Zaretskii
2016-06-24 11:17 ` Paul Eggert
2016-06-24 13:43 ` Eli Zaretskii
2016-06-24 21:34 ` Paul Eggert
2016-06-25 7:48 ` Eli Zaretskii
2016-06-25 21:34 ` Paul Eggert
2016-07-02 9:50 ` Eli Zaretskii
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