GNU bug report logs - #9983
valgrind warning in draw_glyphs

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From: Dan Nicolaescu <dann <at> gnu.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 9983 <at> debbugs.gnu.org
Subject: bug#9983: valgrind warning in draw_glyphs
Date: Mon, 07 Nov 2011 06:52:03 -0500

Eli Zaretskii <eliz <at> gnu.org> writes:

>> From: Dan Nicolaescu <dann <at> 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?

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