From: Dan Nicolaescu <dann@gnu.org>
To: Eli Zaretskii <eliz@gnu.org>
Cc: 9983@debbugs.gnu.org
Subject: bug#9983: valgrind warning in draw_glyphs
Date: Mon, 07 Nov 2011 07:44:49 -0500 [thread overview]
Message-ID: <yxq1utkdrum.fsf@fencepost.gnu.org> (raw)
In-Reply-To: <yxqhb2g40bg.fsf@fencepost.gnu.org> (Dan Nicolaescu's message of "Mon, 07 Nov 2011 06:52:03 -0500")
Dan Nicolaescu <dann@gnu.org> writes:
> Eli Zaretskii <eliz@gnu.org> writes:
>
>>> From: Dan Nicolaescu <dann@gnu.org>
>>> Date: Sun, 06 Nov 2011 23:36:42 -0500
>>>
>>> The warning is for this:
>>> if (check_mouse_face
>>> && mouse_beg_col < start && mouse_end_col > i)
>>>
>>> it looks like mouse_beg_col and mouse_end_col could be left uninitialized a few lines above.
>>
>> I don't see how. These variables are initialized in this block:
>>
>> if (row >= mouse_beg_row && row <= mouse_end_row)
>> {
>> check_mouse_face = 1;
>> mouse_beg_col = (row == mouse_beg_row)
>> ? hlinfo->mouse_face_beg_col : 0;
>> mouse_end_col = (row == mouse_end_row)
>> ? hlinfo->mouse_face_end_col
>> : row->used[TEXT_AREA];
>> }
>>
>> check_mouse_face starts as zero, and is only set to 1 in this block.
>> So any test that is conditioned on check_mouse_face being non-zero is
>> okay with looking at mouse_beg_col and mouse_end_col.
>>
>> The other variables in the line being flagged, `start' and `i', are
>> also okay: `start' is one of the call arguments and `i' is computed
>> right before the line being flagged.
>>
>> Did I miss something?
>
> Hmm, you might be right. Telling valgrind to attach gdb at that point:
>
> (gdb) info local
> overlap_hl = <optimized out>
> hlinfo = <optimized out>
> mouse_beg_col = 0x0
> check_mouse_face = 0x0
> dummy_x = 0x0
> h = <optimized out>
> t = <optimized out>
> mouse_end_col = 0x50b3a22
> head = 0x7feffe3a0
> tail = 0x7feffe3a0
> s = <optimized out>
> clip_head = 0x0
> clip_tail = 0x0
> i = <optimized out>
> j = <optimized out>
> x_reached = 0x184
> last_x = 0x2ec
> area_left = 0x1c
> f = 0x5157bf0
>
> Maybe a compiler problem, evaluating the && in the wrong order?
The assembly in question looks like this:
.LBB3664:
.loc 1 22981 0
movl -152(%rbp), %ebx
cmpl %ebx, -260(%rbp)
jge .L7265
movl -192(%rbp), %eax
testl %eax, %eax
je .L7265
.loc 1 22982 0
movslq -232(%rbp), %rax
.loc 1 22985 0
xorl %r14d, %r14d
cmpq %rax, -120(%rbp)
setl %r14b
leal (%r14,%r14,2), %ebx
movl %ebx, -144(%rbp)
the debugger is stopped on the "jge" line, that means that the "cmpl"
lined did the access.
(gdb) p/d (long long)&mouse_beg_col - (long long)$rbp
$18 = -260
(gdb) p/d (long long)&check_mouse_face - (long long)$rbp
$19 = -192
so it looks like check_mouse_face is tested after mouse_beg_col.
(unless I'm missing something...)
The compiler here is the system compiler on an up to date Fedora15 system.
gcc --version
gcc (GCC) 4.6.1 20110908 (Red Hat 4.6.1-9)
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
next prev parent reply other threads:[~2011-11-07 12:44 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-07 4:36 bug#9983: valgrind warning in draw_glyphs Dan Nicolaescu
2011-11-07 5:49 ` Eli Zaretskii
2011-11-07 11:52 ` Dan Nicolaescu
2011-11-07 12:44 ` Dan Nicolaescu [this message]
2011-11-07 12:59 ` Andreas Schwab
2011-11-07 15:21 ` Dan Nicolaescu
2011-11-07 15:54 ` Eli Zaretskii
2011-11-07 12:21 ` Andreas Schwab
2011-11-07 15:57 ` Eli Zaretskii
2011-11-08 14:17 ` Dan Nicolaescu
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