New warning

New warning

[Po Lu]

Since a previous commit, I get:

../../emacs/src/window.c: In function ‘window_wants_header_line’:
../../emacs/src/window.c:5546:19: warning: potential null pointer dereference [-Wnull-dereference]
 5546 |               || !null_header_line_format (BVAR (XBUFFER (WINDOW_BUFFER (w)),
      |                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 5547 |                                                  header_line_format), f))
      |                                                  ~~~~~~~~~~~~~~~~~~~~~~~

Would someone please look into this?
Thanks.

Re: New warning

[Eshel Yaron]

Po Lu <luangruo@yahoo.com> writes:

> Since a previous commit, I get:
>
> ../../emacs/src/window.c: In function ‘window_wants_header_line’:
> ../../emacs/src/window.c:5546:19: warning: potential null pointer dereference [-Wnull-dereference]
>  5546 |               || !null_header_line_format (BVAR (XBUFFER (WINDOW_BUFFER (w)),
>       |                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  5547 |                                                  header_line_format), f))
>       |                                                  ~~~~~~~~~~~~~~~~~~~~~~~
>
> Would someone please look into this?
> Thanks.

Hmm, clang doesn't emit this warning (and I didn't try compiling with
gcc before submitting that patch, sorry about that).

The following seems to silence this warning with gcc 13.1, but I'm not
sure I fully understand why/when WINDOW_BUFFER might return NULL, so I'm
not sure it's the right thing to do... Any insights?

diff --git a/src/window.c b/src/window.c
index 81578375498..644fcab9d04 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5540,6 +5540,7 @@ window_wants_header_line (struct window *w)
 	  && !WINDOW_PSEUDO_P (w)
 	  && !EQ (window_header_line_format, Qnone)
 	  && (!null_header_line_format (window_header_line_format, f)
+	      || !WINDOW_BUFFER (w)
 	      || !null_header_line_format (BVAR (XBUFFER (WINDOW_BUFFER (w)),
 						 header_line_format), f))
 	  && (WINDOW_PIXEL_HEIGHT (w)

Re: New warning

[Eli Zaretskii]

> From: Eshel Yaron <me@eshelyaron.com>
> Cc: emacs-devel@gnu.org
> Date: Tue, 06 Jun 2023 18:59:14 +0300
> 
> Po Lu <luangruo@yahoo.com> writes:
> 
> > Since a previous commit, I get:
> >
> > ../../emacs/src/window.c: In function ‘window_wants_header_line’:
> > ../../emacs/src/window.c:5546:19: warning: potential null pointer dereference [-Wnull-dereference]
> >  5546 |               || !null_header_line_format (BVAR (XBUFFER (WINDOW_BUFFER (w)),
> >       |                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >  5547 |                                                  header_line_format), f))
> >       |                                                  ~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Would someone please look into this?
> > Thanks.
> 
> Hmm, clang doesn't emit this warning (and I didn't try compiling with
> gcc before submitting that patch, sorry about that).
> 
> The following seems to silence this warning with gcc 13.1, but I'm not
> sure I fully understand why/when WINDOW_BUFFER might return NULL, so I'm
> not sure it's the right thing to do... Any insights?

WINDOW_BUFFER returns a Lisp object, so using !WINDOW_BUFFER is wrong
(and will cause compilation errors with some configure options).  You
want to use either BUFFERP (WINDOW_BUFFER (w)) or
NILP (WINDOW_BUFFER (w)).

In which case this is AFAIU a bogus warning, since we already test
WINDOW_LEAF_P.  So I'm not sure what exactly did GCC see there (my
version of GCC doesn't emit any warnings there).  And I don't know how
to ask GCC which part triggered the warning.

Re: New warning

[Eli Zaretskii]

> Date: Tue, 06 Jun 2023 19:14:11 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: luangruo@yahoo.com, emacs-devel@gnu.org
> 
> > From: Eshel Yaron <me@eshelyaron.com>
> > Cc: emacs-devel@gnu.org
> > Date: Tue, 06 Jun 2023 18:59:14 +0300
> > 
> > Po Lu <luangruo@yahoo.com> writes:
> > 
> > > Since a previous commit, I get:
> > >
> > > ../../emacs/src/window.c: In function ‘window_wants_header_line’:
> > > ../../emacs/src/window.c:5546:19: warning: potential null pointer dereference [-Wnull-dereference]
> > >  5546 |               || !null_header_line_format (BVAR (XBUFFER (WINDOW_BUFFER (w)),
> > >       |                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >  5547 |                                                  header_line_format), f))
> > >       |                                                  ~~~~~~~~~~~~~~~~~~~~~~~

I've now tried on two different systems, with and without
optimizations, with GCC 9.2 and 11.3, and none of those produce this
warning.  What version of GCC do you have there, Po Lu?

Re: New warning

[Andreas Schwab]

On Jun 06 2023, Eli Zaretskii wrote:

> I've now tried on two different systems, with and without
> optimizations, with GCC 9.2 and 11.3, and none of those produce this
> warning.

Did you configure with --enable-checking?  Try without.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: New warning

[Eli Zaretskii]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: luangruo@yahoo.com,  me@eshelyaron.com,  emacs-devel@gnu.org
> Date: Tue, 06 Jun 2023 19:53:44 +0200
> 
> On Jun 06 2023, Eli Zaretskii wrote:
> 
> > I've now tried on two different systems, with and without
> > optimizations, with GCC 9.2 and 11.3, and none of those produce this
> > warning.
> 
> Did you configure with --enable-checking?  Try without.

Thanks.  Stupid GCC.

Re: New warning

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Tue, 06 Jun 2023 19:14:11 +0300
>> From: Eli Zaretskii <eliz@gnu.org>
>> Cc: luangruo@yahoo.com, emacs-devel@gnu.org
>> 
>> > From: Eshel Yaron <me@eshelyaron.com>
>> > Cc: emacs-devel@gnu.org
>> > Date: Tue, 06 Jun 2023 18:59:14 +0300
>> > 
>> > Po Lu <luangruo@yahoo.com> writes:
>> > 
>> > > Since a previous commit, I get:
>> > >
>> > > ../../emacs/src/window.c: In function ‘window_wants_header_line’:
>> > > ../../emacs/src/window.c:5546:19: warning: potential null pointer dereference [-Wnull-dereference]
>> > >  5546 |               || !null_header_line_format (BVAR (XBUFFER (WINDOW_BUFFER (w)),
>> > >       |                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> > >  5547 |                                                  header_line_format), f))
>> > >       |                                                  ~~~~~~~~~~~~~~~~~~~~~~~
>
> I've now tried on two different systems, with and without
> optimizations, with GCC 9.2 and 11.3, and none of those produce this
> warning.  What version of GCC do you have there, Po Lu?

GCC 13.1.1.

Thanks.